The day and night profile of calcium and phosphate metabolism in older Gambian adults

ING Staff: Inez Schoenmakers, Jean Redmond, Landing Jarjou, Kerry Jones, Yankuba Sawo, Ann Prentice

Calcium and phosphate metabolism is interlinked with bone metabolism and both are regulated by common factors (eg parathyroid Hormone, fibroblast growth factor 23 and vitamin D metabolites). The kidney plays a key role as a target tissue and is a source of these factors.

An increase in PTH secretion induced by poor vitamin D status and/or low calcium intake predisposes older people to osteoporosis. However, our research has shown that the incidence of osteoporotic fracture is low in Gambian and Chinese and populations, despite elevated plasma PTH concentrations.

We have recently investigated potential resistance to the bone-resorbing effects and racial differences in PTH dynamics in older men and women in The Gambia, UK and China, through stimulation of PTH secretion by oral phosphate loading and demonstrated ethnic differences in bone and mineral metabolism. The mechanisms are unclear. Differences in circadian profile may have influenced the response to phosphate loading because circadian patterns for several calciotropic hormones, and bone markers have been described, mainly in Caucasian populations.

In these detailed metabolic studies the circadian rhythm of calciotropic hormones and bone metabolism in 15 men and 15 women aged 60-75 years will be characterised. Parallel studies are being carried out in the UK and in China.

The findings will provide further insight into potentially important ethnic differences in kidney and bone metabolism, which may impact on skeletal health and other outcomes such as blood pressure.

 

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