Cohort studyindependent cross-checkabstract checked I-SUP-116 standard review
Vitamin C pills and kidney stones
Total, Dietary, and Supplemental Vitamin C Intake and Risk of Incident Kidney Stones.
Overview
Ferraro PM et al.. Am J Kidney Dis 2016 · PMID 26463139 · DOI 10.1053/j.ajkd.2015.09.005
Men taking 1,000 mg or more of vitamin C a day had about 19% more kidney stones; no link was seen in women.
Does the study support the specific claim? Partly · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
To link vitamin C intake to kidney stones.
- How was the study done?
Three large cohort studies.
- How many people, animals or samples were studied?
About 197,000 adults.
- What was actually found?
Higher stone risk with high-dose vitamin C in men only.
- How large was the observed effect?
HR 1.19 (1.01-1.40).
- What do the results mean in everyday life?
Avoid high-dose vitamin C if prone to stones.
- What are the study's limitations?
Observational; questionnaires.
- What does it say about Elawady's specific claim?
Supports part of C-SUP-07.
- Do the results apply to Germany and Europe?
Applicable.
- What can explicitly not be concluded from this study?
Cannot prove that vitamin C causes stones.
Scientific in-depth review
1. Full reference
- Authors
- Ferraro PM et al.
- Journal
- Am J Kidney Dis
- Year
- 2016
- Identifier
- PMID 26463139 DOI 10.1053/j.ajkd.2015.09.005 · PMC4769668
- Verification
- verified – PubMed efetch 2026-10-26; Crossref works API 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
No COI statement in PubMed record; funding listed: NCI NIH HHS, NIDDK NIH HHS
2. Research question
Are total, dietary and supplemental vitamin C intakes associated with incident kidney stones?
3. Study design and population
- Study design
- Cohort study – Prospective cohort analysis (NHS I, NHS II, HPFS)
- Population
US nurses and health professionals
- Country
USA
- Period
Median follow-up 11.3-11.7 years
- Sample size
156,735 women and 40,536 men; 6,245 incident stones
- Inclusion and exclusion criteria
Participants of NHS I/II and HPFS
4. Methods and endpoints
- Exposure / intervention
Total, dietary and supplemental vitamin C
- Comparator
Lowest intake / no supplement use
- Endpoints
Incident kidney stones
- Statistical methods
Multivariable Cox models
5. Actual results
- Results
Men: total vitamin C 500-999 mg/d HR 1.29 (1.04-1.60), >=1000 mg/d HR 1.43 (1.15-1.79), P trend 0.005; supplemental >=1000 mg/d HR 1.19 (1.01-1.40), P trend 0.001. Women: no significant association. Dietary vitamin C not associated.
- Absolute risks
not reported in abstract
- Authors' conclusion
Total and supplemental vitamin C intake was associated with higher kidney-stone risk in men, but not in women.
6. Strengths
- Large cohorts, long follow-up
- Separates dietary and supplemental intake
7. Weaknesses
- FFQ-based exposure
- Stone composition not known for all
- Observational
8. Risk of bias
- Orienting tool
- ROBINS-E
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Observational; residual confounding.
9. Assessment of the statistical interpretation
Recomputed P for supplemental HR 1.19 (1.01-1.40) about 0.04 (stats/C-SUP-07_harms.py).
10. Relevance to the specific claim
Replicates the vitamin C - kidney stone association for men in large US cohorts.
11. Independent contrary findings
No association in women.
12. Transferability to Germany and Europe
Applicable.
13. Overall methodological judgement
Supports the claim part about vitamin C and kidney stones for men at high doses; observational.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | moderate |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Mechanism (oxalate) and dose threshold.