Most adults, especially those older than 50, appear to be falling short on recommended daily levels of vitamin D, an essential nutrient long known to preserve bones and now increasingly tied to protection against other common ailments, including cancer and rheumatoid arthritis.
And just drinking more vitamin-D fortified milk or juice may not make up the deficit, experts say.
A large, federally funded national health survey has found that vitamin D intakes peak during childhood and teenage years but then decline. Women ages 19 to 50 as well as men and women 51 and older ate the least amount of vitamin D-rich food.
Even when the study accounted for use of vitamin D supplements, few elderly men and women had intakes above the recommended daily levels. The researchers concluded that the low intakes, especially for the elderly, "warrant intervention."
At a time when scientists are discovering a widening role for vitamin D, "many lines of investigation indicate that most Americans do not have optimal levels of vitamin D, mainly because of low sunlight exposure," said Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health.
Vitamin D is made by the skin, which requires ultraviolet light to produce the vitamin from cholesterol.
Because of skin cancer concerns, however, more people wear sunblocks that inhibit production of vitamin D. Dark-skinned people, whose skin pigments protect them from the sun, need to spend a couple of hours in sunlight to make enough vitamin D.
Plus, the skin's ability to make vitamin D declines significantly with age. For that reason, the National Academy of Sciences set the latest vitamin D daily intake at 200 international units (IU) -- about the amount found in two, 8-ounce glasses of skim milk -- for those 19 to 50; 400 IU for those 51 to 70; and 600 for people 70 and older.
But a growing number of scientists believe that most adults 19 and older may need 1,000 IU or more. And where research once suggested a limited health role for vitamin D, today there is increasing evidence that it protects against breast, colon and prostate cancer as well as multiple sclerosis, lupus, rheumatoid arthritis and Type 2 diabetes.
"If just half the chronic diseases laid at the feet of vitamin D pan out, it will be quite significant," said Robert P. Heaney, professor of medicine at Creighton University in Omaha.
