Got Vitamin D?

What if I told you there is a relatively simple means of decreasing your chance of developing Type I and Type II diabetes, as well as multiple sclerosis, colon, breast, prostate and possibly other cancers? This simply therapy has also, in definitive research studies, returned hypertensive patients to normal blood pressure levels.

Recent research shows an estimated 30–80% of the US population is deficient in vitamin D (1). A high prevalence of vitamin D deficiency has been noted worldwide, for all races, even in temperate regions of the globe , and is noted to be particularly high for African-Americans (2).

A study done in Boston, MA, at the end of summer when vitamin D levels should be at their highest showed that 40% of Hispanics, 34% of Whites and 84% of African-American adults were vitamin D deficient. A study of Boston-area children reported that 52% of Hispanic and African-American boys and girls were vitamin D deficient. Studies conducted in India showed that 50–80% of adult Indians and 30–50% of Indian children were vitamin D deficient. And in CapeTown, South Africa, an 80% reduction in the skin’s vitamin D synthetic activity has been noted in the winter compared to the summer.

Most people get their vitamin D from the sun. But this requires unprotected sun exposure between the hours of 10am and 3pm. And during the winter months, for anyone living north of Atlanta, Georgia, USA (33.76° N), the sun angle is too low for production of vitamin D from October through March.

UVB rays in particular are essential for vitamin D production and during winter months, most of the UVB rays are absorbed by the ozone layer (1,2).

Dr. Michael Holick, Ph.D., M.D. notes that people assume a balanced diet provides all necessary nutrients. However, dietary sources of vitamin D are few, including mainly oily fish, sun-dried mushrooms and fortified foods such as orange juice or milk. In a glass of vitamin D-fortified milk there are 100 international units (IU); this amount of vitamin D only raises the blood level of 25-hydroxyvitamin D3 by 1ng/mL.

This is why Holick is a staunch advocate for sun exposure during the summer months when solar radiation helps the skin make vitamin D. (1,2).

Dark-skinned persons have a greater risk of vitamin D deficiency due to the protective nature of darker pigments, with deficiency increasing with increasing degree of pigmentation (1,2).

In addition, recommendations from the World Health Organization and the dermatological community to never have unprotected skin exposed to the sun, has led to many Americans using sunscreen, which, while skin protective, greatly decreases the amount of UVB irradiation gained from sun exposure (1).

In the 1980s and 1990s studies showed that the incidence of colorectal, breast and several other cancers increased for persons living at higher latitudes. Similar increased incidence in prostate cancer was also seen (3).

Vitamin D: It’s All Good

The Garlands (3) and others have looked at blood levels of 25-hydroxyvitamin D3 and shown that levels of 20ng/mL reduce the risk of developing colon, breast ad a variety of other cancers by 30–50%. A daily dose of 1,000IU is estimated to reduce the risk of colon, breast, prostate and ovarian cancer by approximately 50%.

Based on the knowledge that persons living at higher latitudes are also at a greater risk of developing Type 1 diabetes, a researcher in Finland followed the records of a group of children from the 1960s. These children took 2,000IU of vitamin D3 daily for the first year of life. She found that this group had a 78% reduced risk of developing type 1 diabetes (1).

In addition, NHANES III database information showed that increased calcium and vitamin D intake was associated with reduced risk of developing type 2 diabetes (4). Wang et al. showed a 50% reduction in risk of heart attack in persons that are vitamin D sufficient (5). And studies have shown that women and men with the highest levels of 25-hydroxyvitamin D3 reduce their risk of developing multiple sclerosis (MS) by approximately 42% (1).

Persons living at higher latitudes are known to have an increased risk of hypertension (6). This is true in Europe, the U.S. and Australia. Hypertensive patients that used a tanning bed 3 times a week for 3 months saw increased blood levels of 25-hydroxyvitamin D3 by 180% and returned to normal blood pressure. Another group of hypertensive patients that used tanning beds that emitted only UVA rays saw no change in their blood levels of 25-hydroxyvitamin D3 and no change in blood pressure (1).

Ranges of 25-hydroxyvitamin D3 defined as deficient in terms of osteoporosis are <15-20ng/mL, while levels below 30ng/mL have been associated with increased risk of colon cancer (2).

What Does It All Mean?

The take home message? Some sun exposure is good. Dr. Holick recommends 10–15 minutes of unprotected exposure to arms and legs, 2–3 times a week. He says to always wear sunscreen on your face. And after 10–15 minutes, protect the rest of your skin as well. Persons with more skin pigmentation will need longer sun exposure times to derive the vitamin D3 benefit.

Holick and many other experts recommend supplements for the months when the sun is lower in the sky, a minimum 1,000IU of vitamin D3 daily, for children and adults, the amount needed to maintain blood levels of 25–hydroxyvitamin D3 above 30ng/mL. New recommendations are expected to be released May 2010 and Holick expects advised levels to increase. He takes 1,400IU daily.

There are many more interesting details on vitamin D research and it’s anti-inflammatory effects. Check the references (here and elsewhere) for more information. This writer has taken 1,000IU for the past five months, to which I attribute a now pain-free lower back.

Here in the northern hemisphere we’re moving towards the low light season, what some call “vitamin D winter” (2). Maybe it’s time to get vitamin D.


  1. Holick, M. (2008) Alternative Therapies 14, 64–75.
  2. Webb, et al. (1988) J. Clin. Endocrinol. Metab. 67, 373–8.
  3. Garland,C.F. et al. (2006) Amer. J. Publ. Health 96, 252–61.

  4. Pittas, A.G. (2007) J. Clin. Endocrinol. Metab. 92, 2017–29.
  5. Wang, T.J. et al. (2008) Circulation 117, 503–11.
  6. Rostand, S.G. (1997) Hypertension 30, 150–6.
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Kari Kenefick

Kari has been a science writer/editor for Promega since 1996. Prior to that she enjoyed working in veterinary microbiology/immunology, and has an M.S. in Bacteriology, U of WI-Madison. Favorite topics include infectious disease, inflammation, aging, exercise, nutrition and personality traits. When not writing, she enjoys training her dogs in agility and obedience. About the practice of writing, as we say for cell-based assays, "add-mix-measure".

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