Seasonal variation of serum bone GLA protein

The seasonal variation of serum Bone Gla Protein (BGP) was investigated in 15 normal young individuals (seven women and eight men, aged 27-39 years). Serum BGP exhibited a significant seasonal variation of 23% around the yearly mean (p less than 0.001) with zenith in February and nadir in July. Significant seasonal variations were noted also for serum alkaline phosphatase (p less than 0.01) and serum phosphate (p less than 0.01). Serum calcium, bone mineral content (BMC) and creatinine clearance revealed no significant seasonal variation. The seasonal variation of BGP did not follow the variation in serum total alkaline phosphatase. The seasonal variation of BGP has to be taken into account when using the protein as a marker of bone remodelling activity. The variation was probably caused by changes in the production rate of the protein, since the renal excretion of the protein, as reflected in creatinine clearance, remained unchanged throughout the year.