The sunshine vitamin and cancer


Update July 2012 – High doses (800 to 2000 iu) of vitamin D prevent fractures in older people – as long as they take the substance regularly, researchers reported in a study published July 5, 2012 in The New England Journal of Medicine. That said, to me, 800iu daily seems like quite a low dose, and would probably be inadequate for most.

An exciting study was published in 2007 in the American Journal of Clinical Nutrition that indicates that getting enough Vitamin D is important for reducing one’s risk of cancer. Post-menopausal women that took 1100iu on vitamin D daily reduced their risk of cancer by up to 60%, which is nothing short of astounding.

Already the Canadian Cancer Society has suggested that all adults should all take 1000iu of Vitamin D a day in the winter months, and that dark-skinned people should take 1000iu of Vitamin D a day year round. For most, that level may be too low.

We are all biochemically different absorbing Vitamin D differently, get different amounts of sun, eat different diets, and these individual differences will determine Vitamin D status. So when you see your doctor, ask for the blood test if you are supplementing with Vitamin D to ensure your levels are optimal. Optimal levels of 25(OH)D are 50-80 ng/ml.

Vitamin D deficiencies are extremely common, and are also linked to osteoporosis, heart disease, Type 1 and Type 2 diabetes, obesity, infertility, fibromyalgia, chronic fatigue syndrome, depression, autoimmune diseases like multiple sclerosis, rheumatoid arthritis, Crohns disease, and Sjogren’s Disease.

Vitamin D works differently from the other vitamins, as it is converted into and used as a hormone in the body. It controls blood levels of calcium, so if there is not enough calcium in the diet, calcium will be taken from the bones to keep the blood happy.

In the opposite scenario, when calcium levels are high and D levels are low, it is believed that the result may be calcification of joints, arteries, and kidneys.

Vitamin D is a very potent antioxidant – more potent than Vitamin E, and is also very important in immune function and cell repair.

So why have our levels of Vitamin D dropped? We are told to slather ourselves in sunscreen before going out the door, which blocks our ability to synthesize vitamin D. We do need to avoid sun burn, so gradually building up sun-time is a good idea.

We are also told to avoid the midday sun, but it is the UV-B rays that are needed to manufacture Vitamin D, and those rays are only potent enough for Vitamin D synthesis between 10am and 2pm in the warmer months. The only time one can absorb Vitamin D from the sun is when our shadow is shorter than we are. At other times of day only the harmful and damaging UV-A rays hit our skin, so that is the time to use sunscreen.

The higher the latitude, the fewer months of the year that UV-B is strong enough for us to make Vitamin D.

The guidelines to avoid the sun are to avoid skin cancer, but according to John Cannell of the non-profit Vitamin D Council in California, about 1500 Americans die each year of skin cancer, whereas 1500 Americans die each day of the kinds of cancers that could be helped with adequate sun exposure.

And skin cancer is relatively easy to detect and treat. So, are we throwing out the baby with the bathwater? Spending enough time in the sun without letting oneself burn looks to me to be a healthy practice.

Furthermore, it is not possible to overdose in Vitamin D if the source is sun exposure.

Many of the food sources of Vitamin D we are wrongly told not to eat, so diets low in saturated fat may also be low in vitamin D. Increased levels of mono-unsaturated fats and omega 6 polyunsaturated fats decrease the assimilation of Vitamin D from the diet, whereas omega 3 fats and saturated fats aid in its assimilation.

Those with very low cholesterol levels due to statin drugs or otherwise would have difficulty synthesizing Vitamin D, as it is the cholesterol in the skin that converts the UV-B rays into the health-giving vitamin. Might it be through this mechanism that statin drugs are associated with higher risks of cancer?

According to the USDA the best dietary sources of Vitamin D in order of potency include:

  • high vitamin cod liver oil (read the label!)
  • lard (pork fat)
  • pickled Atlantic herring
  • eastern oysters
  • catfish
  • sardines
  • mackerel
  • chinook salmon
  • sturgeon roe
  • shrimp
  • egg yolk (fresh)
  • butter
  • liver

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Lappe JM et al. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial Am J Clin Nutr Vol 85(6) 1586-1591, June 2007.

Lin J. et al. Intakes of calcium and Vitamin D and breast cancer risk in women Arch Intern Med Vol 167(10) 1050-1059, May 2007.

Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety Am J Clin Nutr 1999;69:842-56.

Glerup H, Mikkelsen K, Poulsen L et al. Commonly recommended daily intake of vitamin D is not sufficient if sunlight exposure is limited. J Intern Med 2000;247:260-8.

Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab 1988;67:373-8.

Cantorna MT. Vitamin D and autoimmunity: is vitamin D status an environmental factor affecting autoimmune disease prevalence? Proc Soc Exp Biol Med 2000;223:230-3.

Vogelsang H, Ferenci P, Woloszczuk W et al. Bone disease in vitamin D-deficient patients with Crohn’s disease. Dig Dis Sci 1989;34:1094-9.

Bettica P, Bevilacqua M, Vago T, Norbiato G. High prevalence of hypovitaminosis D among free-living postmenopausal women referred to an osteoporosis outpatient clinic in northern Italy for initial screening. Osteoporos Int 1999;9:226-9.

Kinuta K, Tanaka H, Moriwake T, Aya K, Kato S, Seino Y. Vitamin D is an important factor in estrogen biosynthesis of both female and male gonads. Endocrinology 2000;141:1317-24.

Gloth FM, III, Alam W, Hollis B. Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder. J Nutr Health Aging 1999;3:5-7.

Sato Y, Kikuyama M, Oizumi K. High prevalence of vitamin D deficiency and reduced bone mass in elderly women with Alzheimer’s disease. Neurology 1997; 49:1273-8.

Sato Y, Asoh T, Oizumi K. High prevalence of vitamin D deficiency and reduced bone mass in Parkinson’s disease.. Bone 1998;23:555-7.

Chiu KC et al. Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction. Am J Clin Nutr. 2004 May, 79(5): 820-5.

Watson KE, Abrolat ML, Malone LL et al. Active serum vitamin D levels are inversely correlated with coronary calcification Circulation 1997;96:1755-60.

Wortsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr 2000;72:690-3.

Bouillon R, Xiang DZ, Convents R, Van Baelen H. Polyunsaturated fatty acids decrease the apparent affinity of vitamin D metabolites for human vitamin D-binding protein. J Steroid Biochem Mol Biol 1992;42:855-61.

Muller K, Bendtzen K. 1,25-Dihydroxyvitamin D3 as a natural regulator of human immune functions. J Investig Dermatol Symp Proc 1996;1:68-71.

Online at The Miracle of Vitamin D Weston A. Price Foundation.

Online at Vitamin D Council

Copyright 2007 Vreni Gurd


  1. Ted Hutchinson said,

    September 27, 2009 @ 2:27 pm

    I think it is interesting to note that Dr Cannell of The Vitamin D Council has put his name to a version of Vitamin D Plus which you will see includes 250iu of vitamin A daily.
    However it is worth listening to what Dr Cedric Garland has to say on the topic of vitamin a here 24minutes into this video presentation
    Vitamin D Prevents Cancer: Is It True? you will hear him discussing the Vitamin A Contraindications with regard to vitamin D3.
    My view is that naturally we would have obtained the bulk of our vitamin D from near full body sun exposure. We would naturally have obtained some Vitamin d and Vitamin a from eating oily fish. While there are historic references to cod liver oil going back to the 1700’s, mass consumption only occurred after the 1930’s following the discovery of Vitamin D and it’s role in rickets prevention. Raw molecularly distilled or fermented CLO are available.
    But I still think most Vitamin D3 should be made on the skin from UVB acting on cholesterol.

  2. Vreni said,

    September 27, 2009 @ 2:55 pm

    Thanks, Ted! I think your last paragraph is bang on. Watching the video now.

  3. Greg Gillan said,

    September 27, 2009 @ 4:49 pm

    What about tanning beds in the winter months? Does this provide a comparable level of UVB to natural sunlight?

  4. Vreni said,

    September 27, 2009 @ 8:06 pm

    Hi Greg,

    I don’t think most commercial tanning beds provide enough UVB, although Dr. Mercola sells one specifically made for that purpose so they do exist. Here is the link if you want one.

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