Does dietary calcium cause renal stones?
Q When I advised a patient to take extra calcium as part of her menopausal health she asked whether she would be more likely to get renal stones, which run in the family. Is this likely?
A Renal stones can certainly result from abnormalities of calcium metabolism but it is debatable whether taking extra calcium in the diet is a cause of kidney stones.
Stones that contain calcium may result because of an excess of calcium in the blood (hypercalcaemia) or the urine (hypercalciuria). Disorders of the parathyroid are an uncommon but important cause of hypercalcaemia but this 'hyperparathyroidism', or an excess of parathyroid hormone, are easily detected by blood tests.
Hypercalciuria may be idiopathic, but one important cause is excessive absorption of calcium from the intestines. Here the problem seems to be with the intestines rather than because of an excessive intake of dietary calcium.
One study found an inverse relationship between the amount of calcium in the diet and the formation of kidney stones, that is the higher the amount of dietary calcium the lower the risk of kidney stones. The reason for this is that higher amounts of dietary calcium are not necessarily absorbed from the intestines.
Some patients with high urinary calcium levels will respond to a low-salt diet. Other foodstuffs containing oxalate (spinach, cranberries, tea, cocoa and nuts) should be kept to a minimum.
In patients where there is no biochemical abnormality the best advice is to keep up oral fluid intake.
Your patient should be able to have normal dietary intake of calcium but it would be wise to avoid excessive amounts.
Mr Chris Dawson is a consultant urologist at Edith Cavell Hospital, Peterborough, Cambridgeshire