A prospective study of the intake of vitamins C and B6, and the risk of kidney stones in men.
Level 3 - non-randomized controlled study
Prospective cohort study without dramatic effect size
What was done
Researchers conducted a prospective cohort study of 45,251 men aged 40 to 75 years with no prior history of kidney stones. Baseline intake of vitamin C and vitamin B6 from dietary sources and supplements was measured in 1986 using a semiquantitative food frequency questionnaire. Participants were followed for 6 years to document incident symptomatic kidney stones.
What was found
Over 6 years of follow-up, 751 incident kidney stone cases were identified. Neither vitamin showed a statistically significant association with kidney stone risk. Comparing the highest to lowest intake categories, the age-adjusted relative risk (RR) for vitamin C (>=1,500 mg/day vs. <250 mg/day) was 0.78 (95% CI, 0.54 to 1.11). For vitamin B6 (>=40 mg/day vs. <3 mg/day), the age-adjusted RR was 0.91 (95% CI, 0.64 to 1.31). Further adjustment for other stone risk factors did not materially change these estimates.
Why it matters
These findings suggest that high-dose consumption of vitamin C or vitamin B6, whether from diet or supplements, does not increase the risk of symptomatic kidney stones in older men.
Limits
The observational design cannot rule out residual confounding or recall bias inherent in self-reported dietary questionnaires. The cohort consisted exclusively of older men, so findings cannot be directly generalized to women or younger demographics. Stone composition and biochemical stone risk markers were not reported in the abstract.
Cited by
- contradicts Two large prospective cohort studies found an association between high vitamin C intake and increased relative risk of kidney stones in multivariate analysis, but found no statistically significant association on univariate analysis.