Archive for the ‘Health and medicine’ Category

Research update

June 2, 2011

Science is ever moving and ever changing, and we’re always finding new things. In this article I’m revisiting some of my past topics with some recent research.



The structure of skin
One of my first articles on thatscienceguy discussed the structure of human skin and how the sun’s radiation affects it. Skin is the largest organ in the human body, and has a critical role in protecting our body from external threats and stopping excessive water loss. The outermost layer, called the stratum corneum, can actually act like a sponge and absorb quite large amounts of water depending on the humidity of the surrounding environment. This ability to absorb water means it needs to be quite flexible, however it needs to balance this flexibility with being robust enough to be able to protect the deeper layers of skin and organs underneath.



Researchers from the Australian National University examined the structure of the stratum corneum to try to understand how its structure allows these dual roles. They found that the keratin filaments which provide skin its structure have a remarkable three-dimensional weave which allows individual fibres to wind and unwind. While the fibres can individually wind and unwind, they do so cooperatively to allow the stratum corneum to breathe without losing structural strength.

The weaving of keratin in its condensed form. From Evans M.E. and Hyde S.T. 2011

The weaving of keratin in its expanded form. From Evans M.E. and Hyde S.T. 2011



Male motor skills
The study which I rated as the strangest of last year investigated the perfect male dance moves to attract women – they even produced videos which demonstrated these moves. Needless to say, it was quite a popular topic!



I explained the importance of that study by likening it to courtship displays by other animals – the males will put on a ‘show’ to demonstrate their prowess to the female, and in the case of humans, dancing may well be one of our courtship displays. But the question remained why exactly do animals (including humans) put on these courtship displays, what exactly are they exhibiting?



Studying the manakin bird, researchers from the University of California Los Angeles found that the female birds preferred to mate with males who performed the courtship display at greater speeds, and were able to tell differences measured in the milliseconds. The speed and energy exertion required by the male to do this courtship display means they have extremely fast heart rates. From this the authors suggested that the courtship display is actually a demonstration of the male’s motor skills, coordination and cardiovascular qualities, and so being able to do it faster shows that the male is stronger and has better quality genes.



And for those wondering what the manakin bird is, from QI:



Sexual attraction
Back at the start of April I blogged about the science of sexual attraction, and in the intervening two months new research has been released which is worth examining.



In the original articles I wrote about the effects testosterone has on males and their attraction to women, and attractiveness to women. Now, new research has shown that men who have higher testosterone are flirtier. Remembering back, testosterone is important for competition between males, so researchers increased men’s testosterone levels by making them compete in computer tasks. The men who showed the highest increases in testosterone as a result of the competition subsequently showed more interest in the woman, made more eye contact with her, smiled more and talked more about themselves. So the testosterone increases induced by competition makes men more attentive to women – maybe this means the best plan before a big date is to do something competitive.



Males have also been found to be able to distinguish whether a female is fertile just from looking at her face. Back in the original articles I wrote how oestrogen levels, which rise during ovulation, slightly change the shape of a woman’s face, making it more rounded and considered as slightly more attractive. Using macaques (a species of monkey), new research has shown that men can recognise these signs of a female’s fertility, but only in faces they are familiar with. Researchers showed male macaques images of females faces which had been classified as being pre-ovulation, during ovulation, or post-ovulation (they found these stages out from measuring the female’s hormones). The male macaques were able to tell the difference between the faces of during ovulation and pre-ovulation, however they could only tell the difference if they were familiar with the particular female. When showed images of an unfamiliar female, they couldn’t tell the difference.



Little is known about the molecular reasons for sexual preference, but research published recently in Nature has investigated how chemicals in the brain may affect who we find attractive. Serotonin, also known as 5-HT, is known to have a huge effect on mood – in fact the most common drug treatment for depression works by making serotonin last longer in the brain. The researchers found that male mice normally prefer female over males as mates. However, when the same breed of mice was modified to make them unable to produce 5-HT, the males lost their sexual preference. When these mice had their 5-HT production restored to normal levels they regained their preference of females over males. This research is the first to show that 5-HT may be involved in sexual preference, and raises the question of whether other brain chemicals are involved in sexual preference.


Lapping dogs
And finally, another update from the strangest research studies from last year, this time the study which examined how cats drank. They found then that cats used the back of their tongues, skim over the surface of the liquid, and then pull rapidly upwards into their mouth. The surface tension would lift the liquid with their tongue straight into their mouth. This seemed much more refined than the simple scooping method that dogs use.



But do dogs really just scoop liquid? It turns out that comment was premature, as new research has now found. Using high speed video it has now been found that dogs too use a very similar method as cats, picking up liquid with the back of their tongue and relying on surface tension and inertia to keep the liquid in place. The liquid travels with the tongue through the oral cavity into the oesophagus, with the tongue then pressing up against the roof of the mouth to prevent the liquid from falling out.



You can see it all in action in these videos:

This is a 300 fps video of a dog lapping. It seems to show spooning of liquid into the mouth but X-ray video tells a different story. From Crompton A.W. and Musinsky C. 2011




This video shows that, contrary to published accounts, dogs do not scoop liquids into their mouths with a spoon-shaped cavity that forms in the ventral surface of a backwardly directed tongue tip. As in cats, an aliquot of liquid adheres to the dorsal surface of the tongue tip and is transported into the oral cavity as the tongue is rapidly withdrawn. From Crompton A.W. and Musinsky C. 2011

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Medical research funding – worth fighting to protect

April 15, 2011

In an effort to balance an unbalanced budget the Federal Government are said to be planning major cuts to the funds available for National Health and Medical Research Council (NHMRC) research grants. These grants are the major source of research funding in Australia for health and medicine, and any moves to cut this funding will severely damage vitally important Australian research.


Australia has a highly respected reputation worldwide for medical research, being recognised for high quality research and innovation. Despite only having around 1% of the total medical researchers worldwide, it is estimated around 3% of internationally renowned research papers are produced by Australian scientists. By cutting research funding we do put our international reputation at risk, as well as making a noticeable dent in the total research progress of the world. Suzanne Cory, President of the Australian Academy of Science suggests that these cuts, should they go ahead, will send a worrying message internationally that Australia doesn’t take medical research seriously. This is especially true in light of Barack Obama’s recent speeches about the state of the US budget when he reaffirmed the United States’ commitment to science, medical and technological research.


Despite Australia’s international reputation, even before these cuts Australia spends far less than other developed countries. As a proportion of our total national budget, Australia spends only 0.07% on medical research, placing us 8th in the world. As a point of comparison, the US spends 0.22% of their budget on medical research, while Singapore spends 0.23%. This suggests that rather than cuts, Australia should arguably be increasing medical research funding to maintain our international competitiveness. In fact, the cost of research increases by around 6% per year, so failing to at least match this increase already leads to the degradation of Australian research potential.


Speculation is that cuts of $400 million will be made over the next 3 years. While the annual NHMRC grant budget is around $750 million, around two-thirds of that is pre-allocated to maintain grants awarded in previous years. This leaves around $200-250 million each year for new grants, so these proposed cuts would result in around a halving of the money available for new grants to be awarded. At the moment, only around 1 in 5 applications to the NHMRC receive funding, they are extremely competitive and a process in which it is extremely tough to succeed, and reducing this success rate again will devastate Australian research. After a three year period, this has the potential to have reduced the amount of all medical research in Australia by nearly half.


If the government believes it can switch off and switch on research funding at will, it shows that they do not really understand that research just doesn’t work that way. It isn’t a matter of switching off a machine then restarting it a year later, research funding actually pays the salaries of the researchers. By cutting funding, researchers will lose their jobs. And research isn’t something which occurs over a six to 12 month period, a research project is an ongoing endeavour which requires several years of work to contribute to the body of knowledge.  This will particularly affect young emerging scientists who are applying for their first grants. Any delay to a young scientist by not being able to get a research grant will severely affect their career prospects, as time out of research is very damaging and an interrupted research program will stall their ability to make meaningful contributions to their field.


While other countries are showing a commitment to their medical research establishments and Australia is cutting its support, these young Australian researchers will seek opportunities overseas. We already face a brain-drain, which the government laments, where the best and brightest young professionals seek overseas opportunities. Faced with a potentially career damaging loss of funding and a loss of livelihood, young scientists will face no choice but to relocate overseas where they may be able to access greater support, and studies have shown that when researchers relocate overseas, the return rate is far lower. While complaining about the brain drain, cutting medical research funding will exacerbate the problem.


Cutting funding will not only be disastrous for young up-and-coming scientists, but also for established scientists. Projects can involve several years of investigation before bringing together several threads into one significant outcome. Projects which have been funded and building up to major outcomes over the past years may find their funding dry up right when they are about to enter this significant phase. This will reduce the impact that the last decade of funding will have, and sharply reduce the return on the investment the government has already made. This isn’t just about undermining research over the coming years, but also undermining research which has already been done by preventing it coming to its proper conclusion.


Medical research plays an important part of any country’s economy. As has already been pointed out, reducing funding for research will result in serious job losses and the damaging effects this has on the economy. But research itself does contribute to the economy. Barack Obama again likened the economy to an aeroplane, and research and innovation as the engines. The last thing you want to do to an overloaded plane is throw away the engines, and he described medical research as being a “core investment”. UK Chancellor George Osborne agrees, saying “Scientific research … is vital to our future economic success.” The results of medical research funnel back directly into the economy through the commercialisation of new techniques or therapies, with a couple of recent examples being the bionic ear Cochlear and Gardasil. Australia should in fact be moving in this direction and not away from it according to Cathy Foley, President of the Federation of Australian Science and Technological Societies. She points to low skilled manufacture moving away from Australia, and “where Australia is potentially competitive is in drug development, new health technologies where there’s real opportunities for us to reignite a real economic prosperity in health related manufacturing. So from an economic point of view we’re really potentially shooting ourselves in the foot by cutting off those opportunities of creating new industries.” In fact it has been estimated that government investment in medical research provides economic return second only to the mining and retail sectors. Medical research is not a cost, it is an investment, and the returns on the investment are substantial.


Already we’ve discussed several reasons why cutting research funding will weaken Australia without even mentioning the detrimental effects on Australian health. Australian medical research has developed the bionic ear, is making strides toward bionic eyes, developed a vaccine against cervical cancer and resulted in several Nobel prizes – and that is only in recent years. While those are the high profile outcomes from Australian medical research, other results have improved the way doctors treat patients, reduced adverse effects from drugs, reduced wastage in the national pharmaceutical drug subsidy scheme, improved nutrition, helped prevent heart attacks and brain degeneration, and furthered development of anti-cancer drugs, including drugs against skin cancer, prostate cancer and breast cancer. Every single one of these projects (and untold others) have improved the health outcomes of Australians, and research being carried out now will have a role in improving the health of Australians into the future.


Not every research project will directly produce a stunning breakthrough – that is obvious. However, every project provides pieces of the puzzle. Understanding how a cancer cell grows may provide information on how to stop them, or working out how a brain cell integrates signals may help understand mental health disorders or degenerative disorders such as Alzheimer’s. Every piece of information found through research can add to the global knowledge, and may provide the spark for a researcher elsewhere to make that final discovery. Australia has an obligation to the global community to continue to carry out medical research for this reason. Preliminary work carried out in Australia will help researchers overseas, which will then feed back to benefit the Australian population. With an aging population, the health challenges faced by Australia are only going to increase into the future, and it is research now which will help reduce the impact of these challenges. Money spent on research now will save money in the future.


The government is being extremely short sighted if it goes ahead with these cuts. Medical research is vital for not only the health of the Australian population, but for our economy and for our international standing. Reductions to NHMRC funding will cost significant numbers of jobs, and a 3 year cut will continue to affect Australian medical research for a long time into the future. Medical research isn’t a cost; it is an investment, with the outcomes far outweighing what the government puts in. Protecting medical research is something that is worth fighting for, not only by scientists, but the population as a whole. The Discoveries Need Dollars campaign was started by scientists and built amongst scientists, but is a cause which should be supported by everyone.


Support Australia’s valuable medical research, support Discoveries Need Dollars. Visit the website www.discoveriesneeddollars.org and facebook www.facebook.com/discoveriesneeddollars

Thanks to Doug Hilton, Director of the Walter and Eliza Hall Institute, Suzanne Cory, President of the Australian Academy of Science, and Cathy Foley, President of the Federation of Australian Science and Technological Societies. 

Chocolate Week – Part 4

February 19, 2011

So far we’ve looked at the science of making chocolate, the effects it has on your brain, the reasons for cravings and how to overcome those cravings. For Part 4 of Chocolate Week we examine the health benefits of chocolate.

 

Because chocolate contains a high amount of sugar and fats it’s definitely a sometimes food. Not going to deny that at all – it’s important to eat it in moderation. But it is not entirely bad news, because there are some health benefits from eating chocolate, many of which are related to heart health.

 

In two studies released last year, eating around 6 grams of chocolate per day was shown to reduce heart failure and the risk of stroke. For a heart attack, the risk was reduced to around 75% compared to people who ate no chocolate, while the risk of a stroke was reduced by half. These effects were partially a result of reduced blood pressure in people who ate chocolate, however the reduced blood pressure was not the only reason for the reduced risk.

 

The reduced risk of heart failure, stroke, and lowered blood pressure is likely due to chocolate’s ability to thin the blood. Blood contains a type of cell called platelets, which when we cut a blood vessel will clump together and form a blockage to stop blood loss from the cut. However, if the platelets begin to clump together inside the blood vessels they increase blood pressure and cause a blockage in normal blood flow, leading to strokes or heart attacks. By reducing the ability of platelets to clump together inside blood vessels, chocolate can reduce the risk of heart attacks and strokes, and is actually the same way that many pharmaceutical drugs act to achieve the same effect. Dark chocolate is especially effective, with milk chocolate and white chocolate having almost no effect.

 

Adding to this effect of inhibiting platelet clumping, chocolate also improves blood flow by causing blood vessel relaxation. This effect was especially seen in the blood vessels surrounding the heart, the health of which is vitally important in preventing heart attacks. The relaxing of the arteries allows proper blood flow and also further reduces the likelihood of platelet clumping. The pumping action of arteries, important for keeping blood moving around the body, was also found to be improved after eating chocolate. Again, these effects are more pronounced after eating dark chocolate than other types.

 

Chocolate also has effects on insulin, but not what you may expect. Diabetes is a result of insulin resistance, basically the body can’t extract sugar from your bloodstream. Dark chocolate however, in healthy people, increases the ability of insulin to remove sugar from your bloodstream. I’m not going to suggest that diabetics start eating dark chocolate – you should always follow advice from your doctor and not something you read from the internet – but in healthy people it will decrease insulin resistance and allow your body to take up more sugar from the blood.

 

You may think that the fat content of chocolate may increase cholesterol, negating any improvements in heart function. However, one third of the fat found in chocolate is a type which does not change cholesterol production. On the contrary, dark chocolate has actually been found to increase production of HDL, so-called “good” cholesterol, and prevent changes to “bad” cholesterol which would make it even more harmful. These harmful effects of “bad” cholesterol include the formation of plaques inside blood vessels which interrupt blood flow and can lead to heart attacks and strokes. So stopping these modifications to “bad” cholesterol and increasing the amount of “good” cholesterol is another way chocolate can prevent these from occurring.

 

Many of these effects are from chemicals found in chocolate called polyphenols. This group of chemicals are also found in other foods and drinks which have good effects on health, such as tea and red wine. The cacao bean is unusually rich in polyphenols. however much is lost during the fermentation and drying process, and more are lost during the changes in temperature during conching and tempering. Because these chemicals come from the cacao beans, dark chocolate has considerably more than milk chocolate, as would be expected given the higher cacao content of dark chocolate. One study found around 3 times as much polyphenol in dark compared to milk, so if you really wanted to get the benefits of chocolate, stick to the raw beans or dark chocolate. Having tasted raw beans, I’d recommend sticking to the dark chocolate.

 

There are health benefits from eating chocolate, especially for the heart, but there are also downsides from the sugar and fat content. So as with everything, it’s best to keep it in moderation as part of a balanced diet.

 

Chocolate Week recap:

Chocolate Week

Part 1 – Making chocolate

Part 2 – What chocolate does to your brain

Part 3 – Overcoming chocolate cravings

Thanks again to Brendan Somerville and Robyn Vast who provided their knowledge for Chocolate Week and my friends at the RiAus (www.riaus.org.au)

Chocolate Week – Part 3

February 17, 2011

Addicted to chocolate? Or wondering about how you can overcome those cravings? In Part 2 we looked at the effects chocolate has on the brain, including the effects that chocolate has on the brains of cravers and non-cravers. In Part 3 we’re looking at controlling those chocolate cravings.

 

Dieting has been linked to an increase in cravings for “forbidden foods” such as chocolate and people who diet show a larger response to just images of chocolate than non-dieters. The thinking is that by restricting food intake increases the desire for these foods and may also increase feelings of guilt and anxiety. Also, stronger cravings may increase the likelihood of breaking a diet or resuming unhealthy eating behaviour. That’s not to say don’t diet, but the need to learn an effective way to control cravings might be even more important.

 

A recent study by Dr Robyn Vast from the CSIRO looked at the relative effectiveness of self-control of chocolate cravings. Dr Vast recruited 110 self-confessed chocolate addicts and, showing a streak of pure evil, gave each participant a bag of chocolate. In a week’s time the participants had to return the bag for weighing, but were given strict instructions to not eat any of the contents. The difference in weight from the start to the end of the week would show just how successfully each participant had managed to control their cravings.

 

To investigate different strategies for self-control, Dr Vast divided the participants into three groups – one were left to their own devices, another were taught techniques to control their cravings, and the third were told to accept their cravings as part of who they are but realise their brain as a separate entity and their thoughts as just thoughts, identify their cravings as just unhelpful thoughts and to ignore them. Not control the thoughts, but accept them and realise they were just thoughts and not actually something physical. Around 80-90% of our thoughts are negative, and by accepting these thoughts but labelling them as a negative thought and then psychologically discarding them it prevents the thoughts from affecting our emotions.

 

The theory of group 3 is called cognitive defusion, and suggests that accepting thoughts as just thoughts and not something physical may be a way to overcome, or at least minimise, their impact. In a literal sense, when having a chocolate craving we experience it as if we really need chocolate. But if we consider our mind as a separate entity which just produces thoughts, we realise that that we don’t actually need chocolate, it’s just a thought. The next step is to discard a thought we deem as negative.

 

After the week, the success rates for overcoming their cravings and not touching the chocolate were around 43% for the group left to their own techniques and 56% for the group taught control techniques. Incredibly, 81% of the people in the group told to accept their thoughts then discard them as just a negative thought were successful in resisting eating any of the chocolate.

 

So what’s the best way to overcome a chocolate addiction? Not controlling your thoughts, but rather accepting them but think of your mind as a separate entity and not actually experience the thought.

 

There may be another option though. Research from last year suggested another way to overcome cravings – imagination. When people eat a lot of a particular food they begin to reduce their desire for that food and the amount they eat, this effect is called habituation. What has been found is that just imagining eating food will begin to replace the feeling that you actually need to eat it. This effect works for chocolate, if you repeatedly imagine eating chocolate, you will actually eat less of it. The trick is to imagine yourself eating the chocolate, just imagining chocolate by itself will increase cravings and appetite for it, but by imagining eating it, you reduce your desire for it.

 

The take home message from these strategies appears to be the need to accept the thoughts of craving, and that trying to ignore them is a flawed strategy. According to the experts at least, its better to acknowledge the craving and then deal with it.

 

Thanks again to Dr Robyn Vast from the CSIRO for presenting her study data.

Chocolate Week – Part 2

February 16, 2011

Part 2 of Chocolate Week and it’s time to think about what chocolate does to your brain, and chocolate addiction.

 

The effects of chocolate on the brain

Chocolate is thought to affect the brain in a few different ways. It contains compounds which may directly stimulate the brain, and also indirectly changes the way the brain functions.

Really, does it need a caption? It's a brain.

Studies have been done to examine the areas of the brain which become active after eating chocolate, and there are specific regions of the brain which become activated after eating chocolate. These include regions which control pleasure and reward. In fact, people who crave chocolate have higher activation of the pleasure and reward centres than those who do not crave chocolate, even when just seeing chocolate. Areas which control motivation are also increased in activity after eating chocolate, as are areas which control memory storage and retrieval.

Strangely, eating chocolate also causes an increased activation of the motor cortex – the area of the brain which controls voluntary movement. This may not mean however that after eating chocolate people can move better or faster – even just reading a verb which relates to the arm, face or leg will increase activation of the motor cortex.

It is interesting to compare some areas of the brain which are activated by chocolate with those activated by an addictive substance, for example, nicotine. The pre-frontal cortex (the very front area of the brain) is associated with memory and learning, and is potentially involved in the development of addiction. Unsurprisingly nicotine causes activation of this area of the brain. However, there are similarities in the activation of this area when eating chocolate, with activation of this area occurring when eating the chocolate is thought of as being particularly good. Given the addictive nature of nicotine and the adaptations which occur in memory and learning centres of the brain during addiction, this points to a similarly addictive nature of chocolate.

The brain functions by producing chemicals called neurotransmitters which transmit messages from one part of the brain to another. Increased brain activity is due to increased levels of these neurotransmitters. Three major neurotransmitters are called dopamine, serotonin, and opioids – all are commonly affected by drugs and both have been found to be affected by chocolate.

Serotonin has many roles in the brain, including regulating sleep, appetite and mood. There has been evidence that chocolate increases serotonin levels of people who are deficient, including people with seasonal affective disorder or non-typical depression. This increase in serotonin is through an indirect mechanism using the carbohydrates in chocolate (such as sugar); however this effect is counteracted by protein and fat. There is a limit at how much protein or fat a food can contain before it stops this increase of serotonin, and, sadly, chocolate has too much of both, suggesting thatchocolate does not in fact increase serotonin at all.

When activated, opioids cause the release in the brain of endorphins, a chemical which causes a pleasurable feeling. Opioids can be released in the brain in response to sweet foods, including chocolate, and this opioid release caused by sweet foods can lead to an analgesic feeling from endorphin release.

Dopamine is involved in “reward” signalling in the brain, being increased when experiencing favourable things. This increased dopamine makes the brain remember that that was a good thing, and makes you want more; in fact dopamine is increased in anticipation of a good experience, making you want it more and more. Possibly, the sugar content in chocolate causes changes in the dopamine which make this reward signalling stronger, and a stronger reward signal may result in cravings to revisit that feeling. Also, one of the most brain-active chemicals in chocolate activates the dopamine system, further suggesting that dopamine signals may be involved in the effects of chocolate.

There have been suggestions that as chocolate contains a type of chemical called cannabinoids, that it may have a mild effect similar to marijuana. However, while chocolate does indeed contain very low levels of cannabinoids, not enough is absorbed by the body to produce any sort of effect on the brain. Similarly, other compounds which can act on the brain are present in chocolate, however do not contribute to any euphoria caused by eating chocolate, nor do they contribute to cravings as they are found in greater amounts in other foods which do not cause cravings.

 

Mood eating

Unsurprisingly moods do affect the amount of chocolate people eat, but the effect may be the opposite of what you think. When people were happy, they actually ate significantly more chocolate than people were unhappy, and the chocolate was reported to taste better and be more stimulating. While there is evidence that eating chocolate may temporarily improve bad feelings, there is a slump back afterwards and the improvement is very minor. This minor temporary relief can be extremely short, with some studies showing the improvement can be only while you’re actually eating, and as soon as people stopped eating they slumped back. This effect goes however for any sugary foods, not just chocolate.

In total, the evidence points to chocolate having no effect on improving mood or providing any kind of psychological benefit, and it may actually prolong a bad mood!

 

Chocolate cravings

The texture, aroma and fat and sugar content have been thought to be the predominant factors in causing chocolate cravings. And let’s be honest, they are pretty good. Chocolate does have a perfect combination of sweetness, creamy texture, aroma and taste. Indeed, there have been some studies which show that cravings can be ‘cured’ because of just the sensory experience. However there are other factors, such as magnesium content, and also the release of neurotransmitters, which together with the sensory pleasure of chocolate contribute to chocolate cravings.

 

It tastes, smells, looks and feels awesome, but its not the only reason you crave it.

Some of the areas of the brain may explain why people become addicted or crave chocolate so strongly. The areas of the brain activated include the pleasure, reward and memory centres, and non-stimulation of these areas may result in cravings as the brain seeks to return to that activated and pleasurable state. Also, the dopamine and opioid signalling increased by chocolate contributes to this effect.

Cravings have been suggested to be more a way of seeking the dopamine reward than preventing the negative consequences of not eating. The increased activation of the pleasure and reward centres of the brain in cravers supports this, that the effect on cravers is an increased reward rather than a lower level when not eating chocolate.

Finally, magnesium is found in chocolate at relatively high levels. Cravings may be a way of your body saying it is low in magnesium and it needs more, and the magnesium intake from chocolate has been suggested as being a large factor in satisfying chocolate cravings.

 

So while the pleasure of eating chocolate plays a role in cravings, there are sometimes actual physiological reasons for why you feel a craving for chocolate. Tomorrow – how to beat those cravings.

What does the sun actually do to your skin? Part 2

February 6, 2011

In part 2 of this series about the effect of UV on skin, we look at skin cancer and the most effective ways to protect yourself from the damaging effects of the sun.

 

Skin cancer

Skin cancer is the most common cancer in the western world, in Australia it affects four times as many people as every other type of cancer combined. In fact Australia has the highest rate of skin cancers of anywhere in the world and it has been estimated that between 60-70% of the population will have skin cancer at some point in their life. The major cause of skin cancer is UV radiation, and despite the success of campaigns such as “slip slop slap”, this rate is increasing.

There are 3 main types of skin cancer, basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and malignant melanoma.

 

From left: Basal cell carcinoma, Squamous cell carcinoma, Malignant melanoma. Images courtesy of the Australasian College of Dermatologists


The first two types, BCC and SCC are tumours which are originally keratinocytes which have become sun damaged and now rapidly grow and divide, with BCC forming from keratinocytes deep in the epidermis, while SCC form from keratinocytes closer to the surface. Malignant melanoma however, is originally a sun damaged melanocyte. The BCC and SCC types make up most skin cancers, together around 96%, with melanoma making up most of the remaining 4%. Despite only being a small fraction of skin cancers, melanoma is responsible for around three-quarters of skin cancer deaths in Australia, a result of its fast growth and ability to spread rapidly through the body.

Keratinocytes and melanocytes both become cancerous from damage caused by UV radiation. In fact, the amount of UV radiation needed to cause damage leading to skin cancer is far less than that needed to cause a sunburn. UV penetrates the cell and damages DNA, which is effectively the instructions for how the cell works. This damage can sometimes be repaired by the cell, however if these repair mechanisms don’t succeed, the damage may be permanent. There are several genes (sections of DNA) in particular which when damaged have a high probability of causing cancerous growth. One gene, called Braf is found to be damaged in between 50% and 80% of melanoma cells, and causes increased growth rates of cancerous cells. Other genes which normally hinder cell growth are also often found to be damaged in skin cancer cells, as are genes which normally cause cancer cells to die. Genes which are involved in DNA repair are also sometimes found to be damaged in cancer cells, as damage in these areas means the cell may not be able to repair other DNA damage properly. These changes to the DNA caused by UV radiation result in cells which have fast, unlimited growth which then form tumours.

 

DNA damage by UV radiation

 

UV also causes changes to the cell processes which regulate its growth. When exposed to UV radiation, skin cells can increase the production of chemicals which increase the speed of cellular growth, not only of the cell producing the chemical, but also of cells around it. UV also causes the increased production of chemicals which cause inflammation, and these can also cause damage to the cell and also act to increase its growth.

While melanin does provide some protection to the skin cells from the effects of UV, even if you’re someone who tans darkly it is still vitally important to properly protect your skin. A dark tan on white skin only provides a protection of around SPF 4, compared to most sunscreens which provide protection of around SPF 30. Also, remembering the structure of skin, for UV radiation to reach and activate the melanocytes means it has to travel through all the layers of epidermis, potentially damaging the keratinocyte cells on the way. The tan is effectively a way of the body trying to protect itself against more damage. So while having a tan will partially protect you, your skin cells have potentially been damaged to get the tan in the first place. This is why many sun experts use the saying “There’s no such thing as a safe tan”, because you may have received cancer-causing damage to get that tan.

Ultraviolet light also causes a reduction in the effectiveness of your immune system. Normally, the immune system has a role in preventing cancer by identifying and then removing cancerous cells from the body. However, when suppressed by UV radiation, the immune system isn’t as effective in removing cancer cells, allowing them to remain and form tumours.

 

Sunscreens

It is important when using sunscreens not to think of them as blocking UV. They are in fact only a filter which reduces the amount of UV which reaches your skin by forming a barrier to UV radiation. The strength of this filtering out of UV is shown by their SPF rating. The SPF number is a ratio of the time or dose of UV required for sunburn of protected skin to the time or dose of UV required for sunburn of unprotected skin. For example a sunscreen with an SPF of 20 means that skin protected by the sunscreen will take 20 times longer to burn compared to skin without sunscreen. Another way of thinking about it is that it is an indication of how much UV is allowed to penetrate your skin. For example, in Australia, the highest SPF rating allowed to be shown on sunscreens is 30+, which means it limits the UV reaching your skin to one-thirtieth of the levels than if you hadn’t been wearing the sunscreen.

 

An SPF30+ broadspectrum sunscreen. Image courtesy of the Cancer Council Australia

 

Internationally, there are products sold which claim to be tanning sunscreens. The way these products work is by only blocking some UV radiation, allowing the remaining UV radiation to pass through. UV radiation which reaches the earth’s surface is classified as two types, UVA and UVB. These tanning products work by filtering out UVB but allowing UVA to pass through the skin to activate the melanocytes. The problems with these products are many. Firstly, they sometimes only have a very low SPF factor (I’ve seen one with an SPF of 2), meaning they give poor sun protection to begin with. Secondly, UVA radiation is the type which causes nearly all of the damage to the skin structure, meaning you have no protection against the premature aging effects of UV. UVA is also responsible for the production of chemicals in the skin called “free oxygen radicals”. These chemicals can cause significant damage to cells, damage which can lead to the onset of skin cancer. UVA also causes the reduced immune system activity that helps skin cancer cells stay alive. Finally, UVA is a strong promoter of cancer growth, meaning that if there are any damaged cells in your skin it will make them grow very quickly, and this effect is particularly seen with melanoma. So while you may think you’re using a sunscreen and will be protected against the bad effects of UV, in practice there is effectively no protection given by tanning sunscreens.

When using a sunscreen it is absolutely vital to use broad-spectrum sunscreens, which filter both UVA and UVB at an equal level, giving the maximum amount of protection against all of the damaging effects of UV.

 

Next time you’re in the sun, just remember what the effect it’s having on your skin. The most effective way of avoiding skin cancer is still by being sunsmart – that is, slip on a shirt, slop on broad spectrum sunscreen and slap on a hat, and avoiding the sun by seeking shade as much as possible between 11am and 3pm. By staying smart in the sun you will be able to reduce the harmful effects of sun exposure, not eliminate, but reduce as much as practically possible, while still getting the beneficial effects of the sun.

 

A great resource for skin cancer information is the Cancer Council Australia website