A Seasonal Variation Study of 25-Hydroxyvitamin D3Serum Levels in Normal Humans

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Abstract
A population residing in the approximate area of Kalamazoo, MI (latitude north, 42° 17′ 29″ longitude west 85° 35′ 14″), was examined to determine the influence of seasonal variation on human 25-hydroxyvitamin D3 serum levels. Males and females, ranging in age from 16–64 yr of age and judged normal based on laboratory evaluation and physical examination, participated in the 12-month study. Measurement of 25- hydroxyvitamin D3;i serum levels was made by high performance liquid chromatography. A correlation coefficient of 0.776 (P = 0.003) was obtained by comparing average monthly 25-hydroxyvitamin D3 serum to average monthly temperatures. A comparison of approximated monthly amounts of sunlight to average monthly hydroxyvitamin D3 serum levels produced a correlation coefficient of 0.747 (P = 0.005). In addition, changes in 25-hydroxyvitamin D3 levels for the population examined fitted a model demonstrated a relationship to sex and a highly significant periodic relationship to time.