SEASONAL-VARIATION OF BIOCHEMICAL INDEXES OF BONE TURNOVER - RESULTS OF A POPULATION-BASED STUDY

Biochemical markers of bone turnover have been shown to provide valuab le information for the diagnosis and monitoring of metabolic bone dise ase. However, these dynamic indexes are influenced by a number of fact ors that need to be dearly identified to improve their clinical useful ness. To evaluate the contributions of anthropometric, life style, and environmental variables on bone turnover, biochemical markers of bone metabolism were determined in a population-based sample of 580 adults , aged 50-81 yr (297 men and 283 women). Subjects were recruited durin g 14 consecutive months within the framework of the European Vertebral Osteoporosis Study. Serum total and bone-specific alkaline phosphatas e (S-BAP), serum C-terminal propeptide of type I collagen, and serum o steocalcin (S-OC) were measured as bone formation markers. Urinary tot al pyridinoline and deoxypyridinoline were included as bone resorption indexes. In females, serum levels of 25-hydroxyvitamin D, were signif icantly higher (P < 0.01) in summer (May-September) than in winter (Oc tober-April), whereas no significant differences were found in males. In both sexes, no seasonal changes were seen in serum PTH. In males, s erum total alkaline phosphatase (P < 0.01), S-BAP (P < 0.001), and S-O C (P < 0.O5)were significantly higher in winter than in summer. During the same period, females had higher values of S-BAP (P < 0.05), S-OC (P < 0.01), and urinary pyridinoline and deoxypyridinoline (P < 0.001, respectively). Univariate analyses of the effects of life style habit s on markers of bone metabolism revealed that in females, regular alco hol consumption and current smoking led to a suppression of markers of bone turnover, whereas in males, only alcohol intake was associated w ith such changes. In contrast, physical activity was associated with h igher levels of bone formation markers and reduced levels of bone reso rption indexes in both sexes. As shown by multivariate regression anal yses, seasonal variations accounted for more of the variability in mos t biomarkers (up to 12%) than any of the other anthropometric or life style factors except age. This effect may be attributed to subclinical vitamin D deficiency during the winter period, which is common in cou ntries of the northern hemisphere. We conclude that seasonal variation contributes significantly to the biological variability of bone turno ver and needs consideration when interpreting the results of bone mark er measurements.