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Harvard Medical School. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women

Created: 22/8/2006
Updated: 22/8/2006


Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women
Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ
Ann Intern Med. 1997 Apr 1;126(7):497-504


  • The incidence of renal stones in women is one third the incidence in men-the reason for this is unknown
  • No studies exist regarding the relation between diet and kidney stones in women
  • Historically a diet high in calcium was suspected of increasing the risk of calcium-containing stones. However, a high dietary intake of calcium appears to be associated with a decreased risk of stone formation
  • This observation may be due to the fact that high calcium binds oxalate in the gut thereby reducing absorption and subsequent urinary excretion of oxalate
  • Calcium supplements increase urinary calcium excretion, and if not taken with meals do not decrease urinary oxalate excretion
  • Other dietary risk factors may include sodium, sucrose, and animal protein
  • Protective dietary risk factors may include potassium, magnesium and fluid
  • Aim of current study was to examine the association between intake of dietary and supplemental calcium and the risk for kidney stones in women


  • Patients in the “Nurses Health Study” cohort were used
  • Prospective study with a 12-year follow-up
  • 91,731 women were included 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
  • Main outcome measure was incident symptomatic kidney stones


  • 903,849 person-years of follow-up were achieved
  • 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)

  • Greater consumption of dairy products decreases symptomatic stone rate in women
  • Apparent protective effect of dietary calcium may be mediated through its effect on oxalate absorption
  • Calcium restriction increases oxalate absorption form the gut and increases oxalate excretion which plays a more important role in than urinary calcium in stone formation
  • NB Dairy products were major source of calcium and also contain phosphorus. Phosphorus may reduce urinary calcium excretion and calcium oxalate supersaturation in patients with absorptive hypercalciuria-it is possible but unlikely that phosphorus may be the protective nutrient
  • Calcium supplements were associated with an increased risk of kidney stones
  • Calcium supplements can decrease oxalate absorption and subsequent excretion if taken with oral oxalate loads
  • Many patients did not consume calcium supplements at meal times
  • If calcium supplements are not taken at the time of oxalate ingestion they may provide little or no protection form oxalate absorption. In addition, calcium absorption (and the risk of stone formation) may be greater when supplements are not taken with food
  • Sodium and sucrose intake were associated with an increased risk of stone formation possibility due to increased calcium excretion
  • Potassium is associated with a reduced stone rate possibly die to reduced calcium excretion or the high alkali content of potassium rich foods-this can increase urinary citrate and inhibitor of urinary calcium crystal formation
  • For a proportion of the follow-up (not entire 12 years) period animal protein was associated with an increase stone rate
  • Animal protein increases urinary excretion of uric acid, calcium and decreases citrate excretion all predisposing to calcium oxalate stone formation


  • High intake of dietary calcium appears to decrease risk for symptomatic kidney stones
  • Supplemental calcium may increase risk
  • However, other factors present in dairy products (the major source of dietary calcium) could be responsible for the decreased risk seen with dietary calcium

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