NEW YORK (Reuters Health) - Many young adults are not getting enough vitamin D, particularly during the winter months, a team of Massachusetts researchers reports.

"We conclude that young adults aged 18 to 29 years have an equal to greater risk of vitamin D insufficiency than do older adults, especially during the winter," write lead study author Dr. Vin Tangpricha of Boston University School of Medicine in Massachusetts, and colleagues.

"This is one of the first studies in the United States revealing a relatively high prevalence of vitamin D insufficiency in young adults," Tangpricha added in an interview with Reuters Health.

Vitamin D, which helps the body to absorb calcium, is added to milk and is also made by the body when skin is exposed to sunlight. Vitamin D deficiency puts people at risk for the bone-thinning disease osteoporosis as well as chronic bone and muscle pains, and may also increase the risk of certain cancers.

To investigate vitamin D insufficiency, the researchers screened 165 men and women during March and April, at the end of winter, and 142 individuals during September and October, at the end of summer.

Tangpricha and colleagues found that vitamin D insufficiency varied according to the season. While 30% of the end-of-winter group were deficient in vitamin D, 11% of the group tested at the end of summer were, according to the report in the June issue of The American Journal of Medicine.

This seasonal variation was strongest among the 18- to 29-year-old study participants, the researchers note. Slightly more than one third (36%) of this group was deficient in vitamin D at the end of winter.

Further, these young adults had a 30% increase in their vitamin D levels from the end of winter to the end of summer, study findings indicate.

The reason for the high vitamin D deficiency among young adults may be because they eat less fortified milk and cereals and oily fish--which are the main sources of the vitamin, the authors speculate. And the seasonal variation in their vitamin D concentrations may be due to their decreased exposure to sunlight during the winter, as well as during the fall and spring. Most of the younger study participants were students, who would typically be attending classes during daylight hours, the report indicates.

In other findings, nearly two-thirds of the end-of-summer group and 58% of the end-of-winter group reported drinking almost two glasses of milk per day, but this was not associated with higher vitamin D levels.

On the other hand, the 4 out of 10 study participants who reported taking daily multivitamin supplements during the summer and winter months had vitamin D levels 30% higher than those who did not take the supplements.

In light of the study findings, "young adults who do not regularly eat vitamin D-containing foods should take a multivitamin, especially during the winter months," Tangpricha said. Getting enough sun is also important, he added. "The recommendation is to have about 10 to 15 minutes of sunlight exposure, then apply sunscreen for skin cancer protection," he said.

SOURCE: The American Journal of Medicine 2002;112:659-662.

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