Raising the Bar

Current vitamin D recommendations may be less than you need.

By Lisa James

June 2009

Vitamin D, once thought of only in the context of building bone strength, has been found to be much more important to health than scientists had believed. Deficiencies in the sunshine vitamin have been linked to all sorts of disorders, the latest example being a 52% increase in risk for metabolic syndrome, a condition linked to heart woes (Diabetes Care 4/14/09 epub ahead of print).

What’s troubling is that subclinical vitamin D deficiencies—those that don’t cause symptoms—are distressingly common. Such deficiencies have been found in everyone from children to the elderly; according to one estimate, 1 billion people worldwide lack adequate amounts of this nutrient (New England Journal of Medicine 7/19/07). There are few good food sources of vitamin D, which is produced in the skin during exposure to sunlight.

A Versatile Vitamin

Scientists have long known that vitamin D helps the body absorb and use calcium, the main mineral found in bone. That’s why a lack of D increases the risk of osteoporosis, in which bones become more prone to fracture, and a precursor condition known as osteopenia.

But an outburst of research—much of it performed within this decade—has found that vitamin D helps control more than 200 genes and that D receptors exist in tissues everywhere in the body, including the immune system, brain, colon, breast and prostate. As a result, we now realize how crucial vitamin D is for disease prevention. The previously cited NEJM overview study found links between D deficiency and cardiovascular disease; cancers of the breast, colon and prostate; autoimmune disorders such as type 1 diabetes and multiple sclerosis; and brain-based disorders such as depression and schizophrenia.

That study was conducted by Michael Holick, MD, professor of medicine, physiology and biophysics at Boston University School of Medicine and one of the world’s pre-eminent vitamin D researchers. Holick is worried about high rates of D deficiency among office workers and others who spend a lot of their time indoors, telling The New York Times that research “shows a lot of people, particularly people who live in northerly places, just aren’t getting enough sunlight to meet their vitamin D needs” (1/28/03).

D’s Day in the Sun

For years the government’s daily recommended intake (DRI) of vitamin D has been set at 400 International Units (IU), the amount needed to stave off such obvious signs of deficiency as rickets, in which weak bones become misshapen. The upper limit has been set at 600 IU.

But a number of studies support vitamin D intake levels much higher than that. One such study, for which Holick was one of the authors, said that healthy men appear to need 3,000 to 5,000 IU on a daily basis and that “current recommended vitamin D inputs are inadequate to maintain serum 25-hydroxycholecalciferol [the form in which vitamin D is used within the body] concentration” (American Journal of Clinical Nutrition 1/03). What’s more, many other investigations have established the safety of higher vitamin D intakes (AJCN 9/07).

The Institute of Medicine is currently sifting through the studies with an eye towards updating the RDIs for vitamin D and calcium; its report is due in September 2010. Fortunately you don’t have to wait that long. Reputable manufacturers are now producing vitamin D in 5,000 IU supplements. Given all that the sunshine vitamin does for your health, you may want to make the switch.