Don’t cut calcium out to prevent kidney stones

21. Don’t cut calcium out to prevent kidney stones

Cost: No cost at all. In fact, it’s easier — no need to constantly watch what foods contain calcium.

In plain terms: People who’ve had calcium oxalate stones are often advised to limit calcium intake, but randomized trials show the opposite. A study with 120 men who repeatedly developed stones divided them into two groups: one ate a normal amount of calcium while cutting back on animal protein and salt; the other followed a traditional low‑calcium diet. After five years, recurrence rates were 12 out of 60 versus 23 out of 60 — meaning the normal‑calcium group had half the risk. UK guidelines also advise against restricting calcium.

Benefit: This five‑year randomized trial enrolled 120 men with recurrent calcium oxalate stones and high urinary calcium levels. One group consumed 30 mmol of calcium daily, reduced animal protein to 52 g per day, and limited salt to 50 mmol of sodium chloride; the control group ate only 10 mmol of calcium daily. Over five years, recurrence occurred in 12/60 versus 23/60 participants. The unadjusted relative risk was 0.49 (95% CI 0.24–0.98; P = 0.04), indicating half the risk with normal calcium intake. Both groups saw a similar drop in urinary calcium — about 170 mg per day — but oxalate excretion fell by 7.2 mg/day in the normal‑calcium group versus a rise of 5.4 mg/day in the low‑calcium group. NICE guideline NG118 states adults should aim for 700–1200 mg of calcium daily; children and teens need 350–1000 mg per day. The perception that cutting calcium is beneficial stems from the intuitive idea that “stones are made of calcium, so less calcium must help.”

Evidence grade: A

Sources: 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>; National Institute for Health and Care Excellence (2019). Renal and ureteric stones: assessment and management. NICE guideline NG118, clause 1.8.1. <https://www.nice.org.uk/guidance/ng118/chapter/Recommendations>

Notes: Caveats: This trial involved only men with recurrent calcium oxalate stones and high urinary calcium; results may not apply to all stone types. Moreover, the intervention group simultaneously reduced protein and salt intake, so some benefits could stem from those changes rather than calcium alone. This advice specifically discourages actively eliminating calcium‑rich foods — it does not advocate extra calcium supplementation. For any need to add calcium pills, consult your physician. Regarding hydration, see Section 16, Item 8: drinking 2.5–3 L of water daily after a stone episode.