Boston University researcher Michael Holick estimates that approximately 1 billion people worldwide are vitamin D deficient. His review article “Vitamin D Deficiency” appears in the July 19, 2007, issue of the New England Journal of Medicine.

It is interesting to note that the term vitamin D is actually a misnomer. Vitamins by definition are essential nutrients that typically cannot be produced in the body and therefore must be obtained through the diet. Vitamin D is produced in skin exposed to sunlight and occurs naturally in only a few foods (butter, egg yolk, fish oil, and human milk). So vitamin D isn’t a vitamin at all, it’s a sterol. Sterols are compounds that behave like fats and are classified as lipids. Cholesterol is a well-known sterol.

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D, is formed in the body from one of two biologically inactive precursors, known as vitamin D3 or cholecaliciferol and vitamin D2 or ergocalciferol. Vitamin D3 is the precursor of choice due to its greater bioactive potential. Many nutrition experts now recommend D3 over D2, and many multivitamins now contain D3.

Current U.S. recommendations issued by the Institute of Medicine (IOM) call for 200 IU (international units) per day for children and adults up to 50 years of age, 400 IU for adults 51 to 70 years of age, and 600 IU for adults 71 years of age or older.

Based on current data, Holick recommends a fourfold increase in the recommended daily intake of vitamin D in all population groups, or at least 800 IU per day.

“Unless a person eats oily fish frequently, it is very difficult to obtain that much vitamin D on a daily basis from dietary sources. (Fortified milk contains approximately 100 IU per 8 ounce serving.) Excessive exposure to sunlight, especially sunlight that causes sunburn, will increase the risk of skin cancer. Thus sensible sun exposure and the use of supplements are needed to fulfill the body’s vitamin D requirements,” said Holick.

What is sensible sun exposure?

Holick describes sensible sun exposure as the exposure of arms and legs for 5-30 minutes (depending on time of day, season, latitude, and skin pigmentation) between the hours of 10 am and 3 pm twice a week.

Given the many variables (time of day, season, latitude, and skin pigmentation) and the risks associated with too much sun exposure, quantifying the amount of sun exposure each individual needs to produce adequate vitamin D is difficult. Additionally, many pediatric care providers are reluctant to recommend sun exposure even for brief intervals.

Is there an alternative to sun exposure?

An alternative to sun exposure is daily supplementation using at least 800 IU of vitamin D3. Holick states that an intake of 1,000-2,000 IU of vitamin D3 per day is safe and that even higher levels may be appropriate for selected groups of individuals. Reports of vitamin D intoxication (too much vitamin D) are rare. While daily intake of more than 50,000 IU of vitamin D3 per day can have adverse side effects, 10,000 IU of vitamin D3 per day have not been shown to cause toxicity.

If you are pregnant or breastfeeding, talk with your health care provider about the amount of vitamin D3 supplement that is appropriate for you and your child. Human milk is one of the few foods that contains vitamin D, but the levels are typically quite low given the fact that breastmilk was never intended to be an infant’s primary source of vitamin D. Recent research shows that supplementing a breastfeeding mother with large amounts of vitamin D3 (4,000 IU per day) can achieve adequate levels of 25-hydroxyvitamin D in the mother as well as her milk.

More research is needed in this area, but the fact remains that adequate levels of vitamin D are essential to long-term health, particularly in view of vitamin D’s role in reducing the risk for a variety of chronic diseases, including cancer, autoimmune disease, osteoporosis, and cardiovascular disease.