Cohort studyindependent cross-checkabstract only checked★ key study I-VEG-05 in-depth review
Dietary oxalate and kidney stones
Oxalate intake and the risk for nephrolithiasis.
Overview
Taylor EN, Curhan GC. J Am Soc Nephrol 2007 · PMID 17538185 · DOI 10.1681/ASN.2007020219
Highest oxalate intake raised stone risk only modestly (about 20%) in some groups; authors: not a major risk factor.
Does the study support the specific claim? No · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Oxalate and stones
- How was the study done?
Cohorts
- How many people, animals or samples were studied?
240,681
- What was actually found?
Modest or no association
- How large was the observed effect?
RR ~1.2
- What do the results mean in everyday life?
Greens not a major stone risk.
- What are the study's limitations?
FFQ
- What does it say about Elawady's specific claim?
Contradicts general claim
- Do the results apply to Germany and Europe?
Moderate
- What can explicitly not be concluded from this study?
Cannot address stone formers specifically.
Scientific in-depth review
1. Full reference
- Authors
- Taylor EN, Curhan GC
- Journal
- J Am Soc Nephrol
- Year
- 2007
- Identifier
- PMID 17538185 DOI 10.1681/ASN.2007020219
- Verification
- verified – PubMed efetch 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
NIH funding
2. Research question
Is dietary oxalate associated with kidney stones?
3. Study design and population
- Study design
- Cohort study – Three prospective cohorts (HPFS, NHS I, NHS II)
- Population
US health professionals
- Country
USA
- Period
Combined 44 years follow-up
- Sample size
240,681 (45,985 men; 92,872 older women; 101,824 younger women); 4,605 stones
- Inclusion and exclusion criteria
Cohort participants
4. Methods and endpoints
- Exposure / intervention
Dietary oxalate (FFQ); spinach
- Comparator
Lowest quintile / <1 serving per month spinach
- Endpoints
Incident kidney stones
- Statistical methods
Cox regression
5. Actual results
- Results
Highest vs lowest oxalate quintile: RR 1.22 (1.03-1.45) men, 1.21 (1.01-1.44) older women, no association in younger women; spinach ≥8 servings/month: RR 1.30 (1.08-1.58) men, 1.34 (1.10-1.64) older women; spinach >40% of oxalate intake.
- Absolute risks
not reported
- Authors' conclusion
Data do not implicate dietary oxalate as a major risk factor for nephrolithiasis.
6. Strengths
- Large
- Repeated FFQ
7. Weaknesses
- FFQ oxalate estimates imprecise
- Self-reported stones
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.
9. Assessment of the statistical interpretation
Modest relative risks.
10. Relevance to the specific claim
Directly tests C-VEG-05.
11. Independent contrary findings
None.
12. Transferability to Germany and Europe
Moderate.
13. Overall methodological judgement
Key evidence.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | some concerns |
| Precision of results | high |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | mixed |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Effect in stone formers.
15. Linked fact checks
- Oxalate-rich greens (spinach, beet greens, chard) cause kidney stones; each 100 mg of dietary oxalate raises urinary oxalate by about 2.7 mg. – Studies contradicting or limiting the claim