Seasonal Change in Osteoid Thickness and Mineralization Lag Time in Ambulant Patients

Low vitamin D levels are common. Bone biopsies taken from 121 ambulant patients were therefore reviewed. Seasonal changes in mineralization correlated inversely with serum 25‐hydroxyvitamin D but not the more active metabolite, 1,25‐dihydroxyvitamin D. This implies that the latter is produced in bone. Introduction: It has been 30 yr since a seasonal variation in osteoid surfaces and calcification fronts was noted in bone biopsies from hip fracture patients in Leeds and attributed to vitamin D status. It was suggested at that time that mild vitamin D deficiency might cause osteoporosis from malabsorption of calcium and more severe deficiency osteomalacia, but little has been published on this subject since. Materials and Methods: We examined bone biopsies, calcium absorption data, and serum vitamin D metabolites in 121 patients attending our osteoporosis clinics in Adelaide. Biopsies were collected from the anterior iliac crest with a Jamshidi needle after two stat oral doses of 1 g of tetracycline 10 days apart, processed into plastic without demineralization, and all parameters were measured by point counting using a Weibel II graticule. Calcium absorption was measured after an oral dose of 5 μCi of 45 Ca in 250 ml of water with 20 mg of calcium carrier. Serum 25‐hydroxyvitamin D [25(OH)D] was measured by radioimmunoassay and 1,25‐dihydroxyvitamin D [1,25(OH) 2 D] by radioimmunoassay after high‐performance liquid chromatography (HPLC). Results: 25(OH)D levels were lower from late autumn to early spring (April to September) than from late spring to early autumn (October to March) (51 ± 23 versus 61 ± 27 [SD] nM; p = 0.040). None of the biopsies yielded a diagnosis of osteomalacia, but osteoid thickness (O.Th.) was greater in the winter than the summer months (8.5 ± 3.6 versus 7.1 ± 2.8 μm; p = 0.015) as was mineralization lag time (MLT; 11.9 ± 5.2 versus 9.5 ± 3.6; p = 0.005). O.Th and log MLT were both inversely related to serum 25(OH)D ( p = 0.014 and 0.036) but not serum 1,25(OH) 2 D. Calcium absorption was related to serum 1,25(OH) 2 D but not serum 25(OH)D. Conclusions: We conclude that circulating 25(OH)D affects the mineralization process, whereas circulating 1,25(OH) 2 D affects bone indirectly through its effect on calcium absorption.