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Skin Cancers and Diet
Part 4: Skin cancers: Vitamin D
What is vitamin D?
Vitamin D is unique among vitamins for several reasons: Firstly, it is not really a vitamin. Vitamins are compounds which the body doesn't make, and which must be obtained from food. But our bodies can make vitamin D through the action of sunlight on cholesterol in our skin, and there is very little found in food unless you eat large amounts of oily fish a day as the Inuit do.
Also, most vitamins are catalysts for chemical reactions or antioxidants; vitamin D is neither of these, but the only known precursor of a steroid hormone, calcitriol, whose function, like all steroid hormones, is to turn protein production on and off, as the body requires. This action means it has a profound influence over a wide range of body processes.
How much do we need?
Today, most light-skinned people in the UK only make about 1,000 IU of vitamin D a day from sun exposure; many people, particularly the elderly or those with darker skins, make much less than that. Compare that with a single, 20-minute, full body exposure to summer sun which will deliver some 20,000 IU of vitamin D into the circulation of most people within 48 hours. Yet the recommended daily amount is a paltry and totally inadequate 400 IU.
There is no escaping the fact that our species evolved naked in sub-equatorial Africa, where the sun shines directly overhead much of the year and where our species must have obtained tens of thousands of IU of vitamin D every day.
As we spread away from those latitudes, our skin lightened in colour to compensate for the lower levels of UVB, but we would still have worked outdoors in sunlight. With the coming of the industrial revolution, however, we began to work indoors; in the last century we started to travel inside cars; in the last few decades, we began to lather on sunblock and consciously avoid sunlight.
There is no doubt now that vitamin D levels in modern humans are not just low ? they are disastrously and unhealthily low.
Vitamin D prevents cancer
In 1941, an American doctor, Frank Apperly, compared cancer death rates in cities at different latitudes across the North America continent, and found a clear pattern: the further they were from the Equator ? and thus the lower the amount of sunshine ? the more cancer there was.[i] Compared to cities between 10° and 30° latitude, cities between 30° and 40° had 85% higher overall cancer death rates; cities between 40° and 50° averaged 118% higher cancer death rates, and cities between 50° and 60° averaged 150% higher cancer death rates.
Studies of US Naval personnel during 1974-1984 showed that those working indoors had 10.6 cases of melanoma per 100,000 while those who worked both indoors and outdoors had the lower rate of 7.0 per 100,000. Findings from this study suggested a protective role for regular exposure to sunlight and fit with laboratory studies that showed that vitamin D suppressed the growth of melanoma cells in tissue culture.
The same team found that lack of exposure to UV sunlight could place some populations at higher risk of breast cancer. Annual age-adjusted mortality rates for breast cancer varied from 17-19 per 100,000 in the South and Southwest to 33 per 100,000 in the Northeast. Risk of fatal breast cancer in the major urban areas of the United States increased as intensity of local sunlight decreased.[ii] They found the same pattern across the USSR.[iii]
A low blood level of vitamin D is known to increase the risk for the development of breast and colon cancer,[iv] pancreatic cancer,[v] and may also accelerate the growth of melanoma.[vi] Because of this, Dr Gordon Ainsleigh in California believes that sunscreens cause more cancer deaths than they prevent. He estimated that the 17% increase in breast cancer observed between 1991 and 1992 may be the result of sunscreen use over the past decade.[vii] He also estimated that 30,000 cancer deaths in the United States alone could be prevented each year if people adopted a regimen of regular, moderate sun exposure.
Insufficient exposure to ultraviolet radiation may also be an important risk factor for other cancers in the USA and in Western Europe. Dr William Grant found that deaths from a range of cancers of the reproductive and digestive systems were approximately twice as high in New England as in the southwest, despite a diet that varied little between regions. According to Dr. Grant's study, northern parts of the United States may be dark enough in winter that vitamin D synthesis actually shuts down completely. Based on his US findings, Dr Grant estimates a quarter of breast cancer deaths in the UK are a result of vitamin D deficiency.[viii]
Although this study focused on white Americans, the same geographical trend affects black Americans, whose overall cancer rates are significantly higher. This should come as no surprise as darker skinned people require more sunlight to synthesise vitamin D. Most people, who have skin that is deeply pigmented, should seek more sunlight for health reasons.
Sunlight reduces cancer death rates
Many papers have reported that solar UVB radiation and vitamin D reduce cancer death rates.[ix] [x] [xi] [xii] [xiii] [xiv] In addition, there is increasing evidence that vitamin D is very useful in increasing survival rates once a cancer has been discovered. Two studies from Norway found that those whose cancer was discovered in summer or autumn lived longer than those whose cancer was discovered in winter or spring.[xv] [xvi] And a study in the USA of those diagnosed with non small-cell lung cancer found a much higher 5-year survival rate for patients with high levels of vitamin D.[xvii]
So, by how much could higher levels of vitamin D in the UK reduce cancer mortality rates? An analysis of the geographic variation of cancer mortality rates in the USA indicates that there are about 50,000-60,000 premature cancer deaths per year due to insufficient UVB and/or vitamin D.[xviii] These numbers represent about one-tenth of all cancer deaths. By looking at the latitudinal variation of vitamin D-sensitive cancer mortality rates for the eastern USA, Canada, France, Germany, Ireland, and the UK, it is estimated that as many as a quarter of all cancer deaths in the UK could be considered due to insufficient sunlight and vitamin D.
There are 13 types of cancer that definitely benefit from sunlight. They are mostly reproductive and digestive cancers. The strongest benefits are with breast, colon, and ovarian cancer. Other cancers which benefit from sunlight include the really big killers: tumours of the bladder, uterus, oesophagus, rectum, pancreas, stomach and non-Hodgkin's lymphoma. It is even well known that vitamin D protects skin cells from pre-cancerous changes.
References
[i]. Apperly FL. The relation of solar radiation to cancer mortality in North America. Cancer Res 1941; 1: 191-5.
[ii]. Garland FC, Garland CF, Gorham ED, Young JF. Geographic variation in breast cancer mortality in the United States: a hypothesis involving exposure to solar radiation. Prev Med 1990; 19: 614-22.
[iii]. Gorham ED, Garland FC, Garland CF. Sunlight and breast cancer incidence in the USSR. Int J Epidemiol. 1990; 19: 820-4.
[iv]. Martinez ME, Willett WC. Calcium, vitamin D, and colorectal cancer: a review of the epidemiologic evidence. Cancer Epidemiol Biomarkers Prev. 1998; 7: 163-8.
[v]. Skinner HG, Michaud DS, Edward Giovannucci E, et al. Vitamin D Intake and the Risk for Pancreatic Cancer in Two Cohort Studies. Cancer Epidemiol Biomarkers Prev 2006; 15: 1688?95.
[vi]. Ainsleigh HG. Beneficial effects of sun exposure on cancer mortality. Prev Med 1993; 22: 132-40.
[vii]. Holborow P. Melanoma and fatty acids. NZ J Med 1991; 104: 19.
[viii]. Grant W. An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet-B radiation. Cancer 2002; 94: 1867-75.
[ix]. Garland CF. More on preventing skin cancer: sun avoidance will increase incidence of cancers overall. BMJ 2003; 327: 1228.
[x]. Grant WB. An estimate of premature cancer mortality in the United States due to inadequate doses of solar ultraviolet-B radiation. Cancer 2002; 94: 1867-75.
[xi]. Freedman DM, Dosemeci M, McGlynn K. Sunlight and mortality from breast, ovarian, colon, prostate, and non-melanoma skin cancer: a composite death certificate based case-control study. Occup Environ Med 2002; 59: 257-62.
[xii]. Hughes AM, Armstrong BK, Vajdic CM, et al. Sun exposure may protect against non-Hodgkin lymphoma: a case-control study. Int J Cancer 2004; 112: 865-71.
[xiii]. Smedby KE, Hjalgrim H, Melbye M, et al. Ultraviolet radiation exposure and risk of malignant lymphomas. J Natl Cancer Inst 2005; 97: 199-209.
[xiv]. John EM, Dreon DM, Koo J, Schwartz GG. Residential sunlight exposure is associated with a decreased risk of prostate cancer. J Steroid Biochem Mol Biol 2004; 89-90: 549-52.
[xv]. Robsahm TE, Tretli S, Dahlback A, Moan J. Vitamin D3 from sunlight may improve the prognosis of breast-, colon- and prostate cancer (Norway). Cancer Causes Control. 2004; 15: 149-58.
[xvi]. Moan J, Porojnicu AC, Robsahm TE, et al. Solar radiation, vitamin D and survival rate of colon cancer in Norway. J Photochem Photobiol B. 2005; 78: 189-93.
[xvii]. Zhou W, Suk R, Liu G, et al. Vitamin D predicts overall survival in early stage non-small cell lung cancer patients. Am. Assoc. Cancer Res. Annual Meeting, Abstract LB-231, 2005.
[xviii]. Grant WB. Insufficient sunlight may kill 45,000 Americans each year from internal cancer. J Cos Dermatol. 2004; 3: 176-8.
