Calcium-Regulating Hormones: Parathyroid Hormone and Calcitonin. In: Nordin BEC, editor. Calcium in Human Biology. London: Springer; 1988. pp. 43-68. [DOI: 10.1007/978-1-4471-1437-6_3]

Positive effects of a chicken eggshell powder-enriched vitamin–mineral supplement on femoral neck bone mineral density in healthy late post-menopausal Dutch women

Although bone metabolism is largely under genetic control, the role of nutrition is considerable. The present study evaluates the effects of chicken eggshell powder, a new source of dietary Ca, and purified CaCO3 on bone mineral density (BMD) of the lumbar spine and hip. Besides BMD we also looked at biochemical markers of bone and Ca metabolism. Both Ca sources were provided in combination with minerals and vitamins including Mg, cholecalciferol and phylloquinone. We designed a randomised, double-blind, placebo-controlled study to take place over 12 months. Healthy Caucasian women (n 85), selected by age (≥50 and <70 years), from the databases of general practitioners were recruited by telephone calls. They had to be at least 5 years post-menopausal, with lumbar spine T-score being >-2·5. At baseline, their mean habitual daily Ca intake was adequate. The women were randomly allocated to: eggshell powder-enriched (group A; n 24), purified CaCO3-enriched (group B; n 22), or a placebo product (group C; n 27). BMD was measured at baseline and then after 6 and 12 months of supplementation as were the biochemical markers bone-specific alkaline phosphatase, amino-terminal propeptide extension of type I collagen, deoxypyridinoline, calcitonin, intact parathyroid hormone, calcidiol, and urinary Ca. After 12 months of supplementation, only mean BMD of the femoral neck in group A was significantly increased (P=0·014) by 1·75 % (95 % CI 0·18, 3·32) compared with a decrease of -0·60 % (95 % CI -1·92, 0·72) in group C. This increase coincided with significant decreases in markers of bone resorption and formation. No significant changes were seen in BMD at other sites, including lumbar spine, nor in groups B and C. No differences were found between groups A and B, or B and C. The present study indicates that healthy late post-menopausal women with an adequate Ca intake at baseline may increase BMD of the hip within 12 months following supplementation with the chicken eggshell powder-enriched supplement.

Changes in parathyroid hormone receptor binding affinity during egg laying: implications for calcium homeostasis in chicken

Parathyroid hormone (PTH) receptor bindings were examined in the membrane fraction of the calvaria and the kidney of the hen by the use of [125I]PTH-related protein (PTHrP) binding assays. The binding specificity, reversibility, and saturation of the receptor were demonstrated. The equilibrium dissociation constant (Kd) and the maximum binding capacity (Bmax) were obtained by Scatchard analyses. In both calvaria and kidney, Kd and Bmax values decreased at 3 h before oviposition in egg-laying hens, but not in nonlaying hens. Administration of 17 beta-estradiol or progesterone in vivo caused a decrease in the Kd and Bmax values. Ionized calcium concentrations in the blood plasma showed a decrease at 13 h before oviposition. The results suggest that the PTH receptor binding in the calvaria and the kidney is affected by ovarian steroid hormones and may play a role in maintaining the calcium homeostasis in the egg-laying hen.

Disorders of calcium and bone metabolism

Calcium levels in blood are maintained within narrow limits by parathyroid hormone, acting on kidney, bone and gut. Our understanding of the mechanisms of these actions has increased greatly in recent years, for example by identification of new hormones (eg 1,25 dihydroxy vitamin D) and by the study of isolated bone cells. Though most clinical disorders of calcium metabolism are now readily diagnosed and many are effectively treated, some serious problems still remain. Foremost amongst these are the early diagnosis of osteoporosis and the treatment of osteoporosis after fractures have occurred. Most disorders of calcium metabolism have ophthalmologic manifestations, sometimes troublesome to the patient, and sometimes diagnostically helpful.