Seasonal change in osteoid thickness and mineralization lag time in ambulant patients

Abstract

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 microCi 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 microm; 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.