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How sunshine can prevent cancer

[From New Vegetarian and Natural Health, Summer 2009/10 issue]

by Roger French


New discoveries of the roles of sunshine and vitamin D in cancer. ‘Slip, slop and slap’ is being turned on its head.


The number of remarkable benefits that vitamin D can provide in protecting us from a wide range of diseases is emerging as the nutrient discovery of the first decade of the new millennia.

At the forefront of recognising this new information and assembling it into digestible form for lay people is the brilliant Dr Joseph Mercola who produces regular, voluminous health e-newsletters. These are free newsletters and can be located through his website, Periodically, we have published in this magazine abridged versions of some of Dr Mercola’s articles.

The following article is condensed from a considerable number of his recent articles related to this extraordinary vitamin.



Vitamin D, once linked only to the prevention of bone diseases such as rickets and osteoporosis, is now recognized as a major player in overall human health.

Having too little – specifically in the form of vitamin D3 – may not have any outwardly obvious signs, yet this vitamin has roles in an incredible array of systems and functions in the body. In addition to its well known role in strong and healthy bones, it is now known to be essential for heart health, cancer prevention, skin health, the pancreas, slowing ageing, proper sleep, the eyes and hair, reproductive health, the vascular system, the respiratory system, the immune system, feelings of wellbeing, weight management, and proper digestion and food absorption. It is a truly marvellous vitamin.

Needless to say, deficiency of vitamin D will mean that body and mind cannot be in optimal health. In fact, its deficiency is implicated in most of the diseases of civilization.

Already well known are the bone diseases, rickets, osteopoenia, osteoporosis and osteomalacia. Not so well known are muscle pain and weakness, about 16 different internal cancers, multiple sclerosis, type-1 diabetes, rheumatoid arthritis, heart disease, obesity, Crohn’s disease, migraine headaches, psoriasis, macular degeneration, infertility, asthma, colds, insomnia, hearing loss, seizures, cystic fibrosis, depression, autism, schizophrenia, Alzheimer’s disease and others. The primary reason for the prominence of vitamin D is that out of 30,000 genes in the human body, it has been shown to influence over 2,000 of them.

At least five studies show that the higher our vitamin D level, the lower our risk of contracting colds, flu and other respiratory tract infections. One of these studies was published in the Archives of Pediatric and Adolescent Medicine, October 2008 (162(10):943-51).

The evidence just keeps pouring in, wrote Dr Mercola on 10th July 2008, that vitamin D is a superstar for your health. Already there are over 500 references showing the effectiveness of vitamin D for cancer alone.

One study found that people with the lowest blood levels of vitamin D were about twice as likely to die from any cause compared to those with the highest levels (Archives of Internal Medicine, June 23, 2008;168(12):1340-1349).



For decades, we’ve been the target of a misinformation campaign from the media and conventional medicine that has created a fear of sunshine. Therefore, most people either intentionally or unintentionally avoid the sun – or smear on sunscreen that blocks the beneficial wavelengths that produce vitamin D in skin.

Research suggests that up to 85% of people in developed countries could be deficient in vitamin D without knowing it, and putting up with impaired health.

Current research suggests that all cells in the body have vitamin D receptors, indicating that every cell needs this vitamin.

Although the significance of vitamin D is gradually coming to be understood by orthodox medicine, few doctors do the blood test, and testing for it is unlikely to become commonplace because there is no patented drug to correct deficiency and provide financial reward for a drug company. Consequently, most people with deficiency will never know that they have a potentially serious problem, or know what is causing their existing problems.

The following is a brief account of the major health impacts of deficiency of vitamin D.

Bone health. Deficiency is well known to be associated with a greater incidence of hip fractures. It has very recently been found that vitamin D is also required for cartilage. Researchers at the Menzies Research Institute in Hobart found that people who do not have enough vitamin D quickly lose the cartilage in their knees, accelerating the development of osteoarthritis.

Roughly half the adult population of Tasmania is deficient in vitamin D, and the researchers estimate that if this was remedied, knee replacement would be delayed by an average of 14 years. The national trend of avoiding the sun, they said, is causing widespread mild levels of vitamin D deficiency, even in Queensland (Tasmanian Older Adult Cohort Study, Arthritis and Rheumatism, May 2009; 60: 1381-89).

Immunity. Naturopath, Robyn Chuter, stated in this magazine (Spring 2009, p. 14 – 16) that vitamin D stimulates white blood cells to inhibit the multiplication of viruses; it also dampens down the release of substances that lead to severe inflammation and fluid accumulation in the lungs. Research in 2009 found that people with very low serum vitamin D levels are 55% more likely to have upper respiratory tract infections (colds or flu) compared to those with normal levels (Ginde AA et al, Arch Intern Med 2009; 169(4): 384-90).

Cancer. Vitamin D plays a role in regulating cell growth and differentiation. Studies show vitamin D deficiency to be associated with four of the most common cancers – breast, prostate, colon and skin.

Autoimmune disorders. Deficiency is a factor in multiple sclerosis, Sjogren’s syndrome, rheumatoid arthritis, thyroiditis and Crohn’s disease.

Diabetes. Deficiency is linked to insulin resistance type-1 diabetes in children.

Heart disease. Insulin resistance is a major factor in the cancers listed above and also heart disease. More heart attacks occur in the winter months when vitamin D levels are lower.

Arthritis. Arthritis of the knee and hip progresses faster in people with lower vitamin D levels.

Infertility and PMS. The latter has been completely reversed by calcium, magnesium and vitamin D.

Fatigue, depression and seasonal affective disorder. Low vitamin D may contribute to chronic fatigue and depression. Seasonal affective disorder has been treated successfully with vitamin D.

Obesity. Vitamin D deficiency depresses the production of leptin, a hormone that signals the brain when fat cells are ‘full’. The brain thinks that more food is acceptable and the eventual result may be obesity.

Syndrome X. Vitamin D deficiency is linked with Syndrome X – a combination of insulin resistance, high blood fats and overweight.



There are two ways to obtain adequate vitamin D – sunlight and supplements. During exposure to sunlight, ultraviolet (UV) rays trigger vitamin D synthesis in the skin. This is the most natural way and the ideal way, and the body self-regulates the amount we receive.

Sunlight causes the ideal form of vitamin D to be produced – vitamin D3 (25-hydroxyvitamin D – or in symbol form, 25(OH)D). However, in high latitudes distant from the equator, there may not be sufficient direct sunlight for months at a time, as, for example, in Tasmania. The alternative is supplementation with vitamin D3, which is easily done, provided precautions are taken against overdosing, because excess is toxic (see below).


The optimal level of vitamin D

The current understanding is that serum 25(OH)D levels should be in the range of 125 – 162 nmol/L (50 to 65 ng/ml in American terms) for optimal health and cancer prevention. Deficiency is when the level is less than 125 nmol/L; excess is greater than 250 nmol/L. The vitamin D level should never be below 80 nmol/L, while below 50 nmol/L is a serious deficiency state.

The only way to determine 25(OH)D levels is though blood tests.

Fortunately, sunshine provides optimal levels naturally because the body has a built-in ‘fail-safe’ mechanism which shuts down production when blood levels are optimal. Vitamin D is manufactured from cholesterol in the skin, and if this cholesterol is exposed to the sun for long enough, instead of becoming vitamin D3, it is converted to other compounds (lumisterol or tachysterol), which are biologically inert.

In other words, if you stay out in the sun for a long time, your body will produce the same amount of vitamin D as if you been in the sun for only a moderate time. This mechanism, one of the body’s remarkable self-regulations, makes it virtually impossible to overdose on vitamin D from sun exposure.

However, vitamin D taken as a supplement bypasses this mechanism and leaves you vulnerable to overdose.

We can tell when we have had enough by our skin turning the first faint tinge of pink. After this, we risk sunburn, which can cause skin damage, and possibly skin cancer.

“It’s a tragedy,” says Dr Mercola, “that dermatologists and sunscreen manufacturers have done such a thorough job of scaring people out of the sun. Their message to avoid the sun as much as possible, combined with an overall cultural trend of spending more time indoors during work and leisure time, has greatly contributed to the widespread vitamin D deficiency that’s seen today.”


The components of ultraviolet radiation

The UV component of sunlight is divided into three wavelength ranges, referred to as UVA, UVB and UVC.

The most dangerous are UVC rays which don’t reach the Earth’s surface or come into contact with life thanks to the ozone layer high in the atmosphere; this is why the ‘hole in the ozone layer’ is of so much concern.

The other two wavelengths, UVA and UVB, do reach the Earth’s surface and are of great interest to us, although they impact us in different ways. UVA rays have a longer wavelength of about 320 to 400 nanometers, and UVB have a shorter wave length of about 280 to 320 nanometers.

UVB are the rays that produces vitamin D in the skin, but they are also the primary cause of sunburn when skin is overexposed to sunlight. They don’t penetrate very deeply, so the more melanin in the skin (from being born with dark skin or having a tan), the less UVB penetrates.

Because of their short wavelength, only about five percent of UVB rays pass through window glass, while sunscreen can block UVB entirely. UVA on the other hand are much more penetrating and can pass through glass – and also cloud.

If you’ve ever become sunburned on a cloudy day, it is from the deeply penetrating UVA, which, although slower than UVB to produce redness, will eventually cause burning. The amount of UVB reaching us depends on the factors that affect sunshine – as mentioned below.


Sun exposure for adequate vitamin D

It is interesting to note that skin pigmentation takes millennia to adapt to the solar UV radiation in any particular geographical region. The problem in Australia, New Zealand and the United States is that most of us have our ancestry in northern Europe, where very low levels of UV have resulted in pale skin to make the most of the UV that is available.

To protect our pale skins from the strong Australian sun, we have been urged to ‘slip, slop and slap’ with the result that we have so reduced our skin production of vitamin D that large numbers of people are deficient in it.

Exposure to sunshine is affected by season, latitude, time of day, cloud cover, smog and use of sunscreens. People living in southern and northern latitudes – above approximately 35˚ – will not be able to get enough vitamin D in winter. This applies to Tasmania and the southern parts of mainland Australia. (Tasmania is latitude 41˚ to 43˚, Melbourne is 37˚ and Sydney is 34˚.)

However, even in sunny climates and summer, many people spend most of the day indoors, and if they do go outside, they are fully clothed.

Further, windows filter out most of the sun’s wavelengths that produce vitamin D, so we can’t count on getting it in the home, office or the car.

Some people have greater needs. Overweight people will have a lot of their vitamin D stored away in their fat. Pregnant women need higher levels for themselves and their babies. Elderly people have reduced ability to generate vitamin D.

Dark-skinned people, who nature designed to live under a tropical sun, are darker skinned due to high levels of melanin, which blocks some of the UV radiation and reduces the production of vitamin D3. For example, Australian Aborigines need considerably more sun than Caucasians to generate sufficient vitamin D.

A common myth is that occasional exposure of face and hands to sunlight is sufficient for obtaining enough vitamin D. For most of us, this is a miserably inadequate exposure. We need to expose large portions of our skin to the sun, and for more than a few minutes.

In strong sunshine, bare skin needs at least 10 – 15 minutes of exposure to direct sunlight every day to produce the vitamin D we need. In milder sunshine, it might be around 15 to 30 minutes per day, with the more of the body exposed, the better, preferably about 40 percent of the skin. This means for men shorts and no shirt, and for women shorts and a sports bra or short tank top. This generally applies to fair-skinned, thin, younger individuals.

If the skin is darker or the person is in high latitudes or there is cloud cover, the time could be two hours a day. But it is necessary to be not using sunscreen (see below).

Due to the body’s regulation mechanism, an equilibrium occurs in white skin within about 20 minutes of ultraviolet exposure, at which point, there might be slight skin redness and no more vitamin D will accumulate. For dark pigmented skin, it can take three to six times longer to reach equilibrium.

When light-coloured skin turns the very lightest shade of pink, it’s time to move into the shade or cover up with long-sleeved shirt, trousers and hat. In any case, it is a good idea to always wear a hat.

In summary, have anywhere from 20 minutes to 2 hours a day, depending on skin type and environmental factors.

The bottom line on vitamin D is that if we are able to get out in the sun for an adequate time each day, our levels should be naturally optimized. However, in the times of the year when sunshine is insufficient, we do need to consider oral supplementation with vitamin D3 (cholecalciferol).


Adequate cholesterol essential

Because vitamin D is made in the skin from cholesterol, a person taking drugs to lower cholesterol or proton pump inhibitors to treat ulcers will have a reduced ability to manufacture vitamin D.


Food sources of vitamin D

Vitamin D is relatively rare in foods, and is only available in very limited quantities in eggs, liver and fatty fish, including salmon, sardines, herring and mackerel, as well as the well known source, cod liver oil. Apart from eggs, these are, of course, all flesh foods. Their vitamin D is similar to that formed on the skin by sunlight.

The environmental and health consequences of eating fish include the facts that fish accumulate mercury and other toxic chemicals, and the world’s fish supply is rapidly being depleted.

In any case, the vitamin D in fish oil, such as cod liver oil, is only mildly effective because the abundant fat-soluble vitamin A that is also in this oil competes with vitamin D and reduces its effectiveness. (International Journal of Low Radiation October 2008; 5(4): 368-394). Nothing matches sunlight as the source of this vitamin.

Generally speaking, dietary sources of vitamin D are insufficient to produce optimal blood levels of the human form, (25(OH)D).


Supplementary vitamin D

If we are unable to get enough vitamin D through sun exposure, which is more likely in winter, the alternative is a high-quality vitamin D supplement. It is important use natural vitamin D3 (cholecalciferol), which is what our bodies make, and to ¬not use synthetic vitamin D2 which is toxic at higher doses.

Overdosing on vitamin D is a serious risk with supplements, so it is essential to know if you are taking the right amount. Too much can lead to bone loss; a 2004 Finnish study found that men with average values of serum 25(OH)D have lower risks of prostate cancer than men with either lower or higher values (Tuohimaa P et al, J Cancer 2004; 108: 104-8). This means that high summertime UVB levels can be a risk factor for prostate cancer, while low wintertime UVB levels can also be a risk.

Having regular blood tests for vitamin D may be inconvenient, but Dr Mercola declares that it is one of the most important things you can do for your health. The bottom line is that the best way to get the right amount of vitamin D is through safe outdoor sun exposure, but being careful not to get sunburned. And if you have a shower after sunbathing, don’t use soap for at least two days.



Malignant melanoma has been increasing at an exponential rate in indoor workers since before 1940. Part of the reason may be indoor exposure to UVA radiation which can pass through windows, in contrast to UVB which is blocked by glass. Only UVB causes vitamin D to be produced.

Because UVA penetrates the skin more deeply than UVB, it is thought to be a much more important factor in photo-ageing, wrinkles and skin cancers. UVA can cause cancerous mutations, and can also break down the vitamin D formed in the skin during outdoor exposure to UVB. But we need every bit of that vitamin D because it is a potent defence against melanoma.

Melanoma cells convert vitamin D to a compound called calcitriol, which inhibits the growth of cancer cells and also causes them to die (known as apoptotis). Very recent research indicates that increased UVA exposure and inadequate vitamin D levels promote melanoma (Medical Hypotheses 72: 2009; 434-443).

The body’s protective mechanism for keeping vitamin D levels in balance depends on the fact that vitamin D3 is formed from exposure to UVB, whereas UVA radiation destroys vitamin D. When we are getting tanned outdoors, we are getting both UVA and UVB at the same time, and the two rays balance each other to prevent overdosing on vitamin D from sunlight.

But when we are indoors or in the car and exposed to sunlight filtered through a window, the glass will filter out the majority of UVB, but minimally filter out the UVA. Consequently, very little vitamin D3 is produced, but the UVA coming through is effectively destroying vitamin D3. This creates the risk of vitamin D deficiency and all the health problems that can go with it, including skin cancer.

Unbalanced UVA is double trouble, because, in addition to destroying vitamin D3, it also increases oxidative stress. It is a primary culprit behind skin cancer and increases photo-ageing of the skin. It’s also what causes the skin to tan, which UVB doesn’t do. This means, incidentally, that vitamin D can be produced without any sign of a tan.


A key to skin cancer prevention is avoid sunburn

Dr Mercola is emphatic about the danger of sunburn: “It is important to stress that you should never get burned and should only implement sun exposure very gradually. While we all benefit from regular exposure to the sun, it is important to recognise that you should always limit your exposure so that you avoid getting burnt. Sunburn has been clearly related to an increased risk of skin cancer.”

Having regular sun exposure and avoiding sunburn should decrease the risk of the dangerous form of skin cancer, melanoma, and also the risk of numerous other common cancers. Remember that, in spite of what dermatologists say about sunshine, our bodies are designed to have regular sun exposure as long as it doesn’t cause burning.

Dietary fat is another significant factor in skin cancer. In Australia, as in the US, people over-consume omega-6 oils, and when sunlight hits these fats it can oxidise them and they become carcinogenic. Omega-6 fatty acids predominate in sunflower, safflower, soya and corn oils, and are consumed in large quantities in polyunsaturated margarines and many other processed foods. Omega-3 oils are not affected in this way, so consuming less omega-6 oils and having more flax oil (or fish oil or krill oil in a non-vegetarian diet) is part of the skin cancer solution.

In addition, the more antioxidants we take in, the lower the risk of sunburn. Foods containing antioxidants boost our ‘internal sunscreen’, the best being an abundance of fresh vegetables and fruits for their antioxidants, other protective nutrients and phytochemicals.

Returning to Vitamin D, its protection against cancer works in several ways:

It increases the self-destruction of mutated cells (which could become cancerous);

It reduces the reproduction of cancer cells and their spread;

It causes cells to become differentiated;

It reduces the growth of new blood vessels which are needed for dormant tumors to turn cancerous.

An internationally recognised research scientist and vitamin D expert, Dr William Grant, PhD, found that about 30 percent of cancer deaths – 2 million worldwide annually – could be prevented with higher levels of vitamin D. Dr Mercola concludes, “I believe the evidence is quite clear … The benefits of normalizing your vitamin D levels far outweigh any risk you may have from optimal sun exposure.”


Safe tanning guidelines

If the skin is unaccustomed to the sun, it is important to expose it regularly, and to very gradually increase the exposure time commencing with just a few minutes. In a matter of weeks, the skin should be able to take normal sun exposure with little risk of skin cancer.

The best time to sunbathe if you have not already built up a base tan is early morning, because you’re less likely to burn. For the greatest benefit, strive to have at least 40 percent of your skin uncovered.

However, once the skin has a base tan, the best time for sun exposure is around noon – which sounds like an extraordinary thing to say. New research shows that this is the best time of day to get an optimal amount of vitamin D from the sun with minimal risk of getting malignant melanoma.

This means that the recommendations given by health authorities – and until now, the Natural Health Society – that sun exposure should be avoided for three to five hours around noon and had only early morning or late afternoon, may be not the best advice (Advanced Experiments in Medical Biology 2008; 624: 86-88).

Dr William Grant explains, “Our recommendation, based on work in England, Norway and the United States, is that the optimal time to be in the sun for vitamin D production is as near to solar noon as possible – between say 10am and 2pm.”

Firstly, because the UVB is more intense around noon, a shorter exposure time is required. Secondly, when the sun is down near the horizon, the protective UVB is filtered out much more than the UVA, and it is the UVA that is highly correlated with melanoma.

Other scientists agree with these findings. An epidemiologist at the Australian National University in Canberra, Robyn Lucas, has said, “I believe we all need a little unprotected time in the sun during the middle hours of the day when the sun is at its highest and the UVB rays can penetrate the atmosphere.”

“Squamous cell carcinoma is linked to lifetime UVB irradiants, whereas melanoma is linked to lifetime UVA irradiants, or sporadic sun burning in youth and things like that,” says Dr Grant. “And so dermatologists, by telling people to put on sunscreen and avoid the mid-day sun, were actually giving recommendations that led to increased melanoma.

Appropriate sun exposure more likely to prevent than cause melanoma

A number of studies have shown that appropriate sun exposure helps prevent skin cancer, and that melanoma occurrence decreases with greater sun exposure. An Italian study, published in the European Journal of Cancer, June 2008, tended to confirm the earlier studies showing improved survival rates in melanoma patients who were previously exposed to more sunlight [at safe levels].

It is significant that melanoma is more common in indoor workers than in outdoor workers, and is also more common on regions of the body that are not exposed to the sun at all. Additionally, if you are genetically predisposed to skin cancer, UVB radiation has been found to delay the appearance of melanoma.

The real cause of the rising melanoma rates is at least partly the fact that people’s vitamin D status is decreasing dramatically. Research shows that although the sun can increase genetic damage in skin, and can cause skin cancer, the body has a cleverly designed system to avert this risk. But when we stay out of the sun entirely, we bypass this system because the key to it is vitamin D. Vitamin D does not have just a slight impact on our cancer risk. It can cut our risk by as much as 60 percent.



Sunscreens can do us a disservice in three ways: they prevent vitamin D production; they still allow sun damage; and most of them contain toxic chemicals.

Because most sunscreens block out UVB, they effectively block the synthesis of vitamin D in the skin and contribute to the widespread vitamin D deficiency. Sunscreens with a sun protection factor (SPF) of 8 or greater will block the UV rays that produce vitamin D.

To make matters worse, many sunscreens allow UVA through and so don’t stop sun damage from occurring. All they stop is the burning. Worse still, a person wearing sunscreen and believing they are protected, is likely to stay out in the sun longer. If the sunscreen does not provide adequate UVA protection, this can further increase the risks of wrinkles and melanoma, without the warning of sunburn to tell the person to get out of the sun. Fortunately, more brands are now including UVA protection, although often at low levels.

If a person has no choice and must be out in the sun long enough to burn, then sunscreen use is appropriate, but it is necessary to use a product that protects against both UVA and UVB. Sunscreens based on titanium dioxide or zinc oxide reflect both types of rays, and have been used worldwide for over 75 years with relative safety.

The Environmental Working Group, a non-profit Washington DC-based organisation that researches skincare health hazards, reports in its ‘2009 Sunscreen Guide’ that three out of five brand-name sunscreens are ineffective, contain hazardous chemicals, or both (


Hazardous ingredients

The Environmental Working Group (see above website) after investigating almost 1,000 sunscreens found that most contain toxic chemicals that are absorbed through the skin and add to the body’s load of toxic chemicals. Some are among the most powerful free-radical generators known to man with the potential to damage health in many ways, including increasing the risk of cancer.

By following the standard recommendations to apply generous amounts of sunscreen every few hours to prevent skin cancer, a person is likely to be absorbing a fair amount of such chemicals. Examples of some of the worst chemicals used in regular brand sunscreens listed in the EWG ‘2009 Sunscreen Guide’ (click on ‘About Active Ingredients’) are:

Oxybenzone – can cause photoallergic reactions;

Octocrylene – produces free radicals when exposed to UV light;

Ensulizole – produces free radicals when exposed to sunlight, and may be carcinogenic;

Padimate O – a derivative of the once-popular PABA sunscreen ingredient, releases free radicals and damages DNA;

Menthyl Anthranilate – produces free radicals when exposed to sunlight;

Sulisobenzone – can cause skin and eye irritation.

In contrast, one of the safer brands of sunscreen, UV Natural, which was rated by the EWG as being among the top ten most effective sunscreens, contains most or all of the following ingredients: zinc oxide; oils of grape seed, safflower, macadamia nut and sesame; white beeswax; Candelilla wax; Carnauba wax; colloidal silica; extracts of green tea; grape seed extract; vitamin E; zinc stearate and iron oxides. UV Natural is cruelty-free, vegan and Australian made and owned. This brand was tracked down by the Natural Health Society and is available from its online store.



When a person has had enough sun – as indicated by the skin turning the lightest shade of pink – the obvious and safest options are to put on a long-sleeved shirt, trousers and hat or move indoors.

If a person has no choice and must be out in the sun longer than this, then sunscreen use is appropriate, and the kind to use is one that protects against both UVA and UVB and is free of harmful ingredients.



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