Intake of vitamins B6 and C and the risk of kidney stones in women

Urinary oxalate is an important determinant of calcium oxalate kidney stone formation. High doses of vitamin B6 may decrease oxalate production, where as vitamin C can be metabolized to oxalate. This study was conducted to exa mine the association between the intakes of vitamins B6 and C and risk of k idney stone formation in women. The relation between the intake of vitamins B6 and C and the risk of symptomatic kidney stones were prospectively stud ied in a cohort of 85,557 women with no history of kidney stones. Semiquant itative food-frequency questionnaires were used to assess vitamin consumpti on from both foods and supplements. A total of 1078 incident cases of kidne y stones was documented during the 14-yr follow-up period. A high intake of vitamin B6 was inversely associated with risk of stone formation. After ad justing for other dietary factors, the relative risk of incident stone form ation for women in the highest category of B6 intake (greater than or equal to 40 mg/d) compared with the lowest category (<3 mg/d) was 0.66 (95% conf idence interval, 0.44 to 0.98). In contrast, vitamin C intake was not assoc iated with risk. The multivariate relative risk for women in the highest ca tegory of vitamin C intake (greater than or equal to 1500 mg/d) compared wi th the lowest category (<250 mg/d) was 1.06 (95% confidence interval, 0.69 to 1.64). Large doses of vitamin B6 may reduce the risk of kidney stone for mation in women. Routine restriction of vitamin C to prevent stone formatio n appears unwarranted.