By Suzanne Rostler
NEW YORK (Reuters Health) – Recommendations for daily vitamin D intake may be too low to prevent deficiencies in some women, researchers in Canada report.
They found that during the winter, many women in Canada had insufficient blood levels of vitamin D despite consuming more than 5 micrograms (mcg) or 200 international units (IU) daily, the recommended intake for adults younger than 50 years of age, in milk or dietary supplements.
A lack of sunlight in northern countries such as Canada increases the importance of dietary vitamin D in preventing rickets and osteoporosis, Dr. R. Vieth from Mount Sinai Hospital in Toronto, Ontario, and colleagues, point out.
"Nutritional laws have been grossly wrong about adult needs for vitamin D," Dr. Vieth told Reuters Health, citing a previous study showing that adults need at least 1000 IU to ensure adequate blood levels of vitamin D.
The current report is published in the December issue of the European Journal of Clinical Nutrition.
The researchers measured blood levels of vitamin D in nearly 800 women between the ages of 18 and 35 years old over the course of a year, and surveyed them about their food and multivitamin intake.
During the winter, low blood concentrations of vitamin D were not related to low vitamin D intake, results show. For instance, 21% of women who consumed no vitamin D were found to have insufficient blood levels of the vitamin, compared with 26% of women who reported some vitamin D intake and 20% of women who said they consumed more than 5 mcg of vitamin D daily.
During the summer, however, women who took multivitamins had higher blood concentrations of vitamin D. The researchers explain that women who were physically active and engaged in outdoor activities where they were exposed to sunlight were also more likely to take multivitamins.
A woman's race did not affect her vitamin D levels in wintertime, but during the summer, fewer white women had insufficient blood levels of the vitamin.
People with darker skin are at greater risk of vitamin D deficiency because they need more sunlight to trigger the reaction in the skin that makes vitamin D. However, all women could benefit from more vitamin D in the diet regardless of their skin tone or country of residence, Dr. Vieth said.
"Low vitamin D levels are simply a side effect of the modern lifestyle in most countries, whether people live in sunny places or not," the researcher added.
Eur J Clin Nutr 2001;55:1091-1097.
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