Model Predicts Individual's Vitamin D NeedsARS News Service
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Your skin tone and the amount of sunshine you receive--in addition to what
foods you eat--all can influence the amount of vitamin D that your body has on
hand for optimum health. In a preliminary and apparently first-of-its-kind
study, Agricultural Research Service (ARS) research physiologist Charles B.
Stephensen and colleagues have developed a preliminary model that predicts an
individual's vitamin D requirements.
Stephensen is based at the ARS Western Human Nutrition Research Center at the
University of California-Davis.
Scientists have known since the early 20th century that our bodies are
stimulated to make vitamin D when ultraviolet rays from the sun reach our skin.
But the amount of direct sunlight that a person receives is affected not only
by the amount of time spent in the sun, but also by latitude, season, skin
pigmentation, and even the amount of protective clothing that one wears.
Some vitamin D comes from food, including salmon and some other fish; milk and
breakfast cereals fortified with this essential nutrient, and nutritional
supplements such as multivitamin tablets.
The current recommended daily allowance of vitamin D for U.S. adults who are
less than 50 years of age is 200 international units.
To develop the preliminary model, Stephensen and co-investigators worked with
72 young adult volunteers who provided intermittent records of what they ate
and, for 7- to 8-week stints, wore photosensitive badges from 7 a.m. to 7 p.m.
so scientists could determine their level of sun exposure.
Data from the volunteers--either African-American or of European ancestry--who
had relatively low amounts of sun exposure suggest that they may need
additional vitamin D to reach a target blood level of 75 nanomoles of vitamin D
per liter of plasma.
Stephensen cautions, however, that some vitamin D levels indicated by the model
exceed the level currently considered safe. More research, with a larger number
of volunteers, may refine the predictive power of the model, he reports.
The research was published earlier this year in the Journal of Nutrition.
ARS is the principal intramural scientific research agency of the U.S.
Department of Agriculture.
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