MONDAY, Nov. 29 (HealthDay News) -- Genetics influence a
person's vitamin D levels during the winter while other factors
have the greatest impact in the summer, the results of a new study
Vitamin D, which is needed to maintain health and for strong
bones, is naturally made by the body when exposed to sunlight. Most
foods do not contain vitamin D unless it's added by
Emory University researchers checked 310 identical twins and 200
nonidentical twins, average age 55, for blood levels of
25-hydroxyvitamin D, a marker of exposure to vitamin D.
Average levels were adequate, but levels were higher in the
summer than in the winter. The researchers said 70 percent of the
variation in vitamin D concentrations in the winter could be
attributed to genetic factors.
However, none of the variation in the summer was due to
genetics, but rather to environmental conditions such as sunlight
exposure and latitude, and other lifestyle factors such as the
amount of vitamin D in the diet.
The study, by Dr. Cristina Karohl and colleagues, is published
in the December issue of the
American Journal of Clinical Nutrition.
Further studies to learn more about how all these factors
influence vitamin D levels would be useful for public health
experts as they consider ways to ensure adequate vitamin D levels
in all populations, the study authors noted in a news release from
the journal's publisher.
The U.S. National Institutes of Health has more about