Most people realize vitamin D is important in calcium absorption and prevention of osteoporosis. Foods that commonly have significant amounts of vitamin D include milk, egg yolk, liver, and fish. Of course, exposure to sunlight causes vitamin D production in our skins. What is not known is vitamin D deficiency is a worldwide problem and is surprisingly common in North America. Vitamin D occurs as 25 hydroxy vitamin D in the blood, and is converted by the tissues into its active form, 1, 25 hydroxy vitamin D. It used to be thought vitamin D conversion occurred in the kidney, but now researchers know that it also exists in numerous tissues such as the colon, breasts, and prostate. In these tissues, vitamin D controls cell proliferation by increasing apoptosis (programmed cell death that is lacking in cancer cells), decreases angiogenesis (new blood vessel proliferation seen in cancer cells), and promotes cell differentiation (this is lacking in cancer cells).
In the mid 1600s in Northern Europe there was a high incidence of rickets in the cities. By 1919 Huldschinsky discovered childhood rickets was cured with sunlight. In the 1930s vitamin D was added to foods and even put in Schlitz beer. The main source of vitamin D is from production in our skins from exposure to sunlight. If a person were to stay in the sun for 1 hour in a bathing suit (without sunblock), 20,000 IU of vitamin D would be produced on average. Using a SPF15 sunblock, 99.9% of vitamin D production is blocked, and if a SPF 8 is used, 97.5% is blocked. So using sunblock basically eliminates the benefit of sun exposure.
Vitamin D deficiency is associated with obesity, and studies have shown that in obese patients with UV light exposure from a tanning bed, only 33% of the vitamin D concentration is produced compared to normal weight individuals. Vitamin D produced in the skin becomes trapped in the subcutaneous fat. Also, after 50,000 IU of vitamin D2 was given, levels in obese patients were 50% of that of normal weight individuals in one study.
A study published in Lancet stated that at a vitamin D blood level of at least 20ng/mL, prostate, colon and breast cancers would be reduced by 30 - 50%. There is an especially strong correlation between digestive organ cancers and vitamin D deficiency. It has also been shown that a combination of vitamin D and calcium reduces the risk of pre-cancerous colonic adenomatous polyps. In this study (JNCI 2003), 1200mg of calcium + serum levels of vitamin D equivalent to 29.1 ng/mL stopped the development of colonic polyps. A study from the University of California at San Diego showed that in the USA, breast cancer rates would decrease by 50% and colon cancer rates by 66% if a person took 2000 IU of vitamin D3 daily.
Low vitamin D levels have also been shown to affect survival in cancers of the breast, colon, prostate, early-stage lung, melanoma, and non-Hodgkin's lymphomas.
Up until recently, the RDA (recommended daily allowance) for Vitamin D has been 400 IU. How was this arrived at? In the 1930s cod liver oil was given to children at a dose of 1 teaspoon daily during the winter to prevent rickets. There are approximately 400 IUs of vitamin D in a teaspoon of cod liver oil, so the RDA became 400 IU. The current government stated upper tolerated dose is 2000 IU/day, but we know from reviews of the medical literature that no toxicity has been seen in doses less than 10,000 IU and no major toxicity occurs in doses below 40,000 IU.
25 hydroxy vitamin D levels are easy to measure by a simple blood test. I would recommend patient's take in enough vitamin D to keep their levels in the upper reference range (around 50ng/dL). Lifeguards have an average vitamin D level in the 80s, and I haven't seen very many unhealthy looking lifeguards. The Center carries both an emulsified vitamin D3 from Biotics Research that has 400 IU per drop, and a capsule from Thorne Labs that has 5000 IU of vitamin D3 per capsule.
