Otherindependent cross-checkabstract checked I-DRY-112 standard review
Genetic study supports dairy-Parkinson's link in men
Dairy Intake and Parkinson's Disease: A Mendelian Randomization Study.
Overview
Domenighetti C et al.. Mov Disord 2022 · PMID 34997937 · DOI 10.1002/mds.28902
OR 1.70 per daily serving; 2.50 in men.
Does the study support the specific claim? Yes · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Test whether dairy causes Parkinson's.
- How was the study done?
Mendelian randomisation.
- How many people, animals or samples were studied?
About 18,000 Europeans.
- What was actually found?
Genetic dairy proxy linked to more Parkinson's in men.
- How large was the observed effect?
OR 1.70 (1.12-2.60).
- What do the results mean in everyday life?
Dairy may modestly raise Parkinson's risk in men.
- What are the study's limitations?
Genetic assumptions; men only.
- What does it say about Elawady's specific claim?
Supports the claim partly.
- Do the results apply to Germany and Europe?
European.
- What can explicitly not be concluded from this study?
Cannot show the size of absolute risk.
Scientific in-depth review
1. Full reference
- Authors
- Domenighetti C et al.
- Journal
- Mov Disord
- Year
- 2022
- Identifier
- PMID 34997937 DOI 10.1002/mds.28902
- Verification
- verified – PubMed efetch 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
MRC and other grants (record).
2. Research question
Is genetically predicted dairy intake associated with Parkinson's disease?
3. Study design and population
- Study design
- Other – Mendelian randomisation using rs4988235 (lactase persistence) in the Courage-PD consortium
- Population
23 studies of European ancestry
- Country
Europe
- Period
n/a
- Sample size
9823 patients, 8376 controls
- Inclusion and exclusion criteria
Courage-PD participants
4. Methods and endpoints
- Exposure / intervention
Genetically predicted dairy intake
- Comparator
Per serving/day
- Endpoints
Parkinson's disease
- Statistical methods
Two-sample MR, dominant model
5. Actual results
- Results
OR per one serving/day 1.70 (1.12-2.60); men 2.50 (1.37-4.56); P-difference with women 0.029.
- Absolute risks
not reported
- Authors' conclusion
Findings provide further support for a causal relationship between dairy intake and higher PD risk, not biased by confounding or reverse causation.
6. Strengths
- Addresses confounding and reverse causation
- Large consortium
7. Weaknesses
- Single variant
- Effect restricted to men
- Pleiotropy of lactase variant possible
8. Risk of bias
- Orienting tool
- none applicable
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
MR assumptions.
9. Assessment of the statistical interpretation
Relative effect per serving; absolute risk of PD remains low.
10. Relevance to the specific claim
Adds causal-inference support to the observational association between dairy and Parkinson's disease, especially in men.
11. Independent contrary findings
Women show no association (I-DRY-113).
12. Transferability to Germany and Europe
European ancestry.
13. Overall methodological judgement
Strengthens the association; absolute risk still small.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | moderate |
| Directness | direct |
| Reproducibility | not replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Mechanism; replication outside Europe.
15. Linked fact checks
- Milk intake, especially low-fat milk, increases the risk of Parkinson's disease (2.3-fold in the Honolulu study). – Studies supporting the claim