Circannual rhythms and interactions of vitamin D metabolites, parathyroid hormone, and biochemical markers of skeletal homeostasis: A prospective study

Recent studies suggest a circannual pattern of bone turnover. To further in vestigate the underlying mechanisms, 41 healthy subjects (25-80 years old) living in a southwestern German city were studied prospectively over a peri od of 18 months. Participants were examined every 4 weeks, and blood and ur ine samples were obtained on each visit. The following parameters were meas ured: serum 25-hydroxyvitamin D-3 [25(OH)D-3], 1,25-dihydroxyvitamin D-3 [1 ,25(OH)(2)D-3], and parathyroid hormone (PTH), as regulators, and serum tot al alkaline phosphatase (TAP), bone-specific alkaline phosphatase (BAP), ur inary total pyridinoline (PYD), deoxypyridinoline (DPD), and the aminotermi nal telopeptide of collagen type I (NTX), as biochemical markers of bone tu rnover. The presence of significant circannual rhythms for the various mark ers was tested using the Pharmfit method. In the total group, 25(OH)D-3, 1, 25(OH)(2)D-3, and PTH as well as BAP, PYD, DPD, and NTX showed a significan t seasonal variation. 25(OH)D-3 revealed the highest amplitude (38.0%) with an acrophase in August. Levels of the biochemical markers and of PTH were highest in winter with amplitudes of up to 17.7% (DPD). Results were most p ronounced in premenopausal women, in subjects <50 years of age, and in subj ects who did show a significant individual rhythm in 25(OH)D-3 levels. No d ifferences were found regarding other anthropometric or life style factors. Correlation analyses revealed strongest associations between the amplitude s of a vitamin D metabolite and a biochemical marker in premenopausal women . We conclude that specific markers of bone turnover show significant circa nnual rhythms. These changes are related directly to variations in the horm onal regulation of skeletal homeostasis. In postmenopausal women and in men , other effects may superimpose the circannual variation of biomarkers of b one turnover.