Serum 25-hydroxyvitamin D levels in normal subjects: seasonal variations and relationships with parathyroid hormone and osteocalcin.

The measurement of human 25-hydroxyvitamin D (25-OH-D) serum levels has a potential role in evaluating calcium and bone metabolism disorders. To determine normal ranges were studied, cross-sectionally, a healthy population of men and women, aged 18-69 years, over a 12-month period. Changes in 25-OH-D levels for the examined population fitted a mathematical model that demonstrated a highly significant periodic relationship to time. Gender had a significant (p < 0.03) effect on mean 25-OH-D concentration, but age was not significantly correlated with 25-OH-D in either sex. A 95% tolerance band was computed in order to have a time-qualified "range of normality" with circannual periodicity. Interesting periodic variations were seen for the parathyroid hormone (PTH) as well as for osteocalcin (OST). A moderate negative correlation was found between 25-OH-D and PTH in both sexes, with more significant evidence in males. No relationship was observed between 25-OH-D and OST.