Greater seasonal cycling of 25-hydroxyvitamin D is associated with increased parathyroid hormone and bone resorption

Summary This analysis assessed whether seasonal change in 25-hydroxyvitamin D concentration was associated with bone resorption, as evidenced by serum parathyroid hormone and C-terminal telopeptide concentrations. The main finding was that increased seasonal fluctuation in 25-hydroxyvitamin D was associated with increased levels of parathyroid hormone and C-terminal telopeptide. Introduction It is established that adequate 25-hydroxyvitamin D (25(OH)D, vitamin D) concentration is required for healthy bone mineralisation. It is unknown whether seasonal fluctuations in 25(OH)D also impact on bone health. If large seasonal fluctuations in 25(OH)D were associated with increased bone resorption, this would suggest a detriment to bone health. Therefore, this analysis assessed whether there is an association between seasonal variation in 25(OH)D and bone resorption. Methods The participants were ( n = 279) Caucasian and ( n = 88) South Asian women (mean (±SD); age 48.2 years (14.4)) who participated in the longitudinal Diet, Food Intake, Nutrition and Exposure to the Sun in Southern England study (2006–2007). The main outcomes were serum 25(OH)D, serum parathyroid hormone (sPTH) and serum C-terminal telopeptide of collagen (sCTX), sampled once per season for each participant. Results Non-linear mixed modelling showed the (amplitude/mesor) ratio for seasonal change in log 25(OH)D to be predictive of log sPTH (estimate = 0.057, 95 % CI (0.051, 0.063), p