Seasonal Variations in Bone Mineral Content after the Menopause

Abstract

PHOTON absorption techniques for measuring bone mineral content in vivo¹ have made possible realistic assessment of short-term sequential changes in skeletal mass in human subjects. Shimmins et al.², using a photon absorption technique to measure the mineral content of the third metacarpal of human volunteers claimed a reproducibility for the method of ± 3% (1 s.d.). In post-menopausal women there is skeletal wasting resulting in an average fall in bone mineral content of about 1% per year³ (post-menopausal osteoporosis⁴). Successive measurements of bone mineral content made in a group of post-menopausal women at six-monthly intervals would be expected to show a mean fall of only 0.5% on each occasion. The difference between any two such measurements should be within the reproducibility of the method, ± 3%. Preliminary investigations using this method for confirming the expected reproducibility of the method gave results very much greater than ± 3%, inferring that either gross technical irregularities had appeared or specific biological changes were occurring. A more detailed investigation of the problem revealed some unexpected and interesting results.