Comparison of Dietary Calcium with Supplemental Calcium and Other Nutrients as Factors Affecting the Risk for Kidney Stones in Women

TLDR

Kidney stone risk in women is poorly understood, but calcium intake is thought to influence stone formation, with evidence suggesting dietary calcium may reduce risk while supplemental calcium may increase it, possibly due to timing of ingestion and other dairy components. The study aimed to evaluate the association between dietary and supplemental calcium intake and the incidence of symptomatic kidney stones in women. A 12‑year prospective cohort of 91,731 Nurses’ Health Study I participants, aged 34–59, was followed for 903,849 person‑years, with dietary intake assessed via repeated self‑administered food‑frequency questionnaires. After adjustment, dietary calcium was inversely associated with stone risk (RR 0.65) whereas supplemental calcium was positively associated (RR 1.20); other nutrients showed sucrose and sodium increased risk, while fluid and potassium decreased risk, indicating high dietary calcium lowers stone risk while supplemental calcium raises it.

Abstract

Calcium intake is believed to play an important role in the formation of kidney stones, but data on the risk factors for stone formation in women are limited.To examine the association between intake of dietary and supplemental calcium and the risk for kidney stones in women.Prospective cohort study with 12-year follow-up.Several U.S. states.91,731 women participating in the Nurses' Health Study I who were 34 to 59 years of age in 1980 and had no history of kidney stones.Self-administered food-frequency questionnaires were used to assess diet in 1980, 1984, 1986, and 1990. The main outcome measure was incident symptomatic kidney stones.During 903,849 person-years of follow-up, 864 cases of kidney stones were documented. After adjustment for potential risk factors, intake of dietary calcium was inversely associated with risk for kidney stones and intake of supplemental calcium was positively associated with risk. The relative risk for stone formation in women in the highest quintile of dietary calcium intake compared with women in the lowest quintile was 0.65 (95% CI, 0.50 to 0.83). The relative risk in women who took supplemental calcium compared with women who did not was 1.20 (CI, 1.02 to 1.41). In 67% of women who took supplemental calcium, the calcium either was not consumed with a meal or was consumed with meals whose oxalate content was probably low. Other dietary factors showed the following relative risks among women in the highest quintile of intake compared with those in the lowest quintile: sucrose, 1.52 (CI, 1.18 to 1.96); sodium, 1.30 (CI, 1.05 to 1.62); fluid, 0.61 (CI, 0.48 to 0.78); and potassium, 0.65 (CI, 0.51 to 0.84).High intake of dietary calcium appears to decrease risk for symptomatic kidney stones, whereas intake of supplemental calcium may increase risk. Because dietary calcium reduces the absorption of oxalate, the apparently different effects caused by the type of calcium may be associated with the timing of calcium ingestion relative to the amount of oxalate consumed. However, other factors present in dairy products (the major source of dietary calcium) could be responsible for the decreased risk seen with dietary calcium.