Don’t give up calcium to prevent kidney stones

People who have had calcium-oxalate stones are often told to eat less calcium; trial results go the other way. Men with recurrent stones who ate normal calcium while cutting animal protein and salt had, over five years, half the recurrence of those on a low-calcium diet. UK guidelines also say not to restrict calcium.

Cost

No money. It even saves effort: you need not watch every day which foods contain calcium.

Benefit

A 5-year randomized controlled trial enrolled 120 men with recurrent calcium-oxalate stones and high urine calcium (idiopathic hypercalciuria). They were randomized into two groups. One ate normal calcium, 30 mmol a day, while also cutting animal protein (52 g a day) and salt (50 mmol sodium chloride a day). The other ate a traditional low-calcium diet, 10 mmol a day. Over 5 years recurrences were 12/60 versus 23/60. Unadjusted relative risk 0.49 (95% CI 0.24–0.98, the credible range), P=0.04 — recurrence risk on normal calcium was half. During follow-up, urine calcium fell about 170 mg a day in both groups. But urine oxalate differed. The low-calcium group rose a mean 5.4 mg a day; the normal-calcium group fell a mean 7.2 mg a day. UK NICE guideline NG118 item 1.8.1 states not to restrict daily calcium intake. Adults keep 700 to 1200 mg a day. Children and teens 350 to 1000 mg a day by age. Giving up calcium looks worthwhile because of the intuition “stones are made of calcium, so eat less calcium.”

Notes

Controversy: The trial was only in men, all with recurrent calcium-oxalate stones and high urine calcium; it does not transfer directly to every stone type. Also the trial arm changed three things at once — normal calcium, less animal protein, less salt — so you cannot credit all benefit to “not giving up calcium.” Low salt and less animal protein may also be working. What to reject is “actively cutting calcium-containing foods,” not “you should take more calcium.” What changed here is calcium in daily meals; calcium supplements are separate — whether someone with past stones should take supplements is a question for the treating doctor. Drinking more water: Section 16, Item 8 (after kidney stones, drink 2.5–3 litres a day).

Sources · 2

1. Borghi L, Schianchi T, Meschi T, et al. (2002). Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. New England Journal of Medicine, 346(2), 77-84. doi.org/10.1056/NEJMoa010369
2. National Institute for Health and Care Excellence (2019). Renal and ureteric stones: assessment and management. NICE guideline NG118，第 1.8.1 条. nice.org.uk/guidance/ng118/chapter/Recommenda…