Dairy products improve retention of calcium in bones

Dear WDDTY:

I wish to point out a number of inaccuracies and misconceptions in Kitty Campion's piece on milk (Second Opinion, vol 5 No 1).

The level of the protein casein in cow's milk is about eight times that in human milk, not 300 as stated (Dairy Research, 1989; 48:519).

Normally, about 3 per cent of calcium passing through the kidneys every day is lost in the urine (about 150 mg/day). This loss is increased by high intakes of dietary calcium, protein and sodium.

It is true, therefore, that dairy products, being rich in calcium and protein, do cause small increases in the urinary excretion of calcium. However, this loss is small and more than compensated by increases in calcium absorbed through the gut, which is stimulated by casein and lactose.

The overall retention of calcium in bone is greater as a result of dairy products, consumption, as a recent paper confirms (BMJ, 1994; 308: 939). Professor M I Gurr, St Mary's, Isles of Scilly......