Don't cut out calcium to prevent kidney stones

Cost

Free. It is actually less trouble, since you don't have to watch every day which foods contain calcium.

What you get

A 5-year randomized controlled trial enrolled 120 men who kept getting calcium oxalate stones and also had high calcium in the urine (called idiopathic hypercalciuria). They were randomly split into two groups. One group ate a normal amount of calcium, 30 mmol a day. This group also ate less animal protein (52 g a day) and less salt (50 mmol of sodium chloride a day). The other group ate the traditional low-calcium diet, 10 mmol a day. Recurrences over 5 years were 12/60 versus 23/60. The unadjusted relative risk was 0.49 (95% CI 0.24–0.98, the plausible range), P=0.04, so the normal-calcium group's risk of recurrence was half. During follow-up, urinary calcium fell by about 170 mg a day in both groups. But the oxalate excreted in the urine differed. In the low-calcium group it rose by an average of 5.4 mg a day, and in the normal-calcium group it fell by an average of 7.2 mg a day. The UK NICE guideline NG118, item 1.8.1, says not to restrict dietary calcium intake. Adults should keep to 700 to 1,200 mg a day. Children and teenagers should have 350 to 1,000 mg a day depending on age. Cutting out calcium looks like a good deal because of the intuition that “stones are made of calcium, so eat less calcium”

Notes

Dispute: this trial was done only in men, all of whom kept getting calcium oxalate stones and had high urinary calcium, so it cannot be applied directly to every type of stone. Also, the trial group changed three things at once: normal calcium, less animal protein and less salt, so not all the benefit can be credited to “not cutting calcium” alone; low salt and less animal protein were working too. What is being ruled out is “deliberately cutting out calcium-containing foods,” not “you should take more calcium.” What is changed here is the calcium in three meals a day. Calcium supplements are a separate matter, and whether someone who has had stones should take them is a question for the doctor treating them. For the item on drinking more water, see §16.8 (after a kidney stone, drink 2.5–3 liters of water a day)

Evidence grade

A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.

Sources

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. https://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. https://www.nice.org.uk/guidance/ng118/chapter/Recommendations

Translated from the Chinese original. Original book, section 6, tip 21. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer