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Eggs and hormone-related cancers: meta-analysis
Egg intake and cancers of the breast, ovary and prostate: a dose-response meta-analysis of prospective observational studies.
Overview
Keum N et al.. Br J Nutr 2015 · PMID 26293984 · DOI 10.1017/S0007114515002135
A possible link with fatal prostate cancer, but small studies may exaggerate it; no link with prostate cancer overall.
Does the study support the specific claim? Partly · Methodological quality: low
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Egg intake and sex-hormone-related cancers
- How was the study done?
Dose-response meta-analysis of prospective studies
- How many people, animals or samples were studied?
18 prospective publications: breast 16,023 cases, ovarian 2,636, total prostate 3,655, fatal prostate 609
- What was actually found?
Per 5 eggs/week: fatal prostate cancer RR 1.47 (1.01-2.14) from 4 studies, with signs of publication bias and not significant under an alternative assumption (1.23, 0.97-1.55); total prostate cancer 1.00 (0.88-1.14); breast 1.05 (0.99-1.11); ovarian 1.09 (0.96-1.24).
- How large was the observed effect?
Random effects; Egger test
- What do the results mean in everyday life?
Not established; keep in perspective.
- What are the study's limitations?
Only 4 studies and 609 cases for fatal prostate cancer; publication-bias signal; no quality assessment of included studies; several studies age-adjusted only; includes the Richman 2011 cohort.
- What does it say about Elawady's specific claim?
Mixed.
- Do the results apply to Germany and Europe?
Moderate.
- What can explicitly not be concluded from this study?
Cannot prove causation.
Scientific in-depth review
1. Full reference
- Authors
- Keum N et al.
- Journal
- Br J Nutr
- Year
- 2015
- Identifier
- PMID 26293984 DOI 10.1017/S0007114515002135
- Verification
- verified – PubMed efetch 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- full text
- Conflicts of interest and funding
Authors declare no conflicts of interest; no funding statement found in the retrieved text.
2. Research question
Egg intake and sex-hormone-related cancers
3. Study design and population
- Study design
- Meta-analysis – Systematic literature search with linear (Greenland-Longnecker) and non-linear (restricted cubic spline) random-effects dose-response meta-analysis of prospective observational studies
- Population
Participants of prospective cohorts, nested case-control/case-cohort and pooled cohort studies (North America, Europe, Asia)
- Country
Multinational
- Period
PubMed and Embase searched to April 2015
- Sample size
18 publications (2 pooled studies): breast 6 (16,023 cases), ovarian 2 (2,636 cases), total prostate 6 (3,655 cases), fatal prostate 4 (609 cases)
- Inclusion and exclusion criteria
Prospective observational or pooled studies of egg intake and incidence of breast, prostate (total, fatal) or gynaecological cancers with >=3 exposure categories or a linear estimate; English language only; abstracts/unpublished excluded; retrospective case-control excluded. 7,378 records screened; 67 full texts excluded with reasons in flow chart.
4. Methods and endpoints
- Exposure / intervention
Egg intake
- Comparator
per 5 eggs/week
- Endpoints
Breast, ovarian, prostate (total and fatal) cancer
- Statistical methods
DerSimonian-Laird random effects; RR per 5 eggs/week; spline models when >=5 studies; Cochran Q and I2; Egger's test and funnel plots; leave-one-out and serving-size (1 vs 2 eggs) sensitivity analyses; no subgroup/meta-regression; no formal risk-of-bias tool for individual studies.
5. Actual results
- Results
Breast: RR 1.05 (0.99-1.11) per 5 eggs/week, I2 0%, P Egger 0.62; non-linear: 1.04 (1.01-1.07) at 5 eggs/week and 1.09 (1.03-1.15) at ~9 eggs/week vs none. Ovarian: 1.09 (0.96-1.24), I2 3%. Total prostate: 1.00 (0.88-1.14), I2 0%, P Egger 0.72. Fatal prostate (4 studies incl. Richman 2011 = A-EGG-11): 1.47 (1.01-2.14), I2 40%, P Egger 0.04 (smaller studies show stronger associations); assuming 2 eggs per serving for 3 studies attenuated it to 1.23 (0.97-1.55), I2 70%.
- Absolute risks
not reported in full text
- Authors' conclusion
Conclusion tempered by possible publication bias and confounding; positive association with fatal prostate cancer cannot be ruled out.
6. Strengths
- Dose-response modelling (linear and non-linear) rather than high-vs-low only
- Prospective designs only, reducing recall bias
- Independent triple screening/extraction; sensitivity analyses on serving-size assumptions
7. Weaknesses
- Fatal prostate estimate based on only 4 studies and 609 cases, with small-study effects (P Egger 0.04)
- Fatal prostate association loses significance under the alternative serving-size assumption (RR 1.23, 0.97-1.55)
- Three prostate studies adjusted for age only; no formal study-level risk-of-bias assessment
- English-only search of two databases; no protocol registration reported
- Mostly single baseline diet measurements; confounding by foods eaten with eggs acknowledged
- Includes the archive-cited Richman 2011 cohort, so it is not independent confirmation of that result
8. Risk of bias
- Orienting tool
- AMSTAR 2
- Type of assessment
- structured assessment based on the full text by a single reviewer (no formal double review)
- Full formal assessment
- no
- Overall risk of bias
- high
- Rationale
AMSTAR 2 overall confidence: critically low (critical flaws in items 2 and 9). Overall raised from some_concerns (abstract-based) to high. Single-reviewer structured judgement; a formal assessment needs two independent reviewers.
| Domain | Judgement | Rationale |
|---|---|---|
| 1 PICO components | low | Clear exposure, outcomes and designs. |
| 2 Protocol established a priori (critical) | high | No registered or published protocol reported; MOOSE guidelines followed. |
| 3 Explanation of included designs | low | Restriction to prospective designs justified. |
| 4 Comprehensive search (critical) | some concerns | PubMed and Embase plus reference lists; English only; no grey literature. |
| 5 Duplicate selection | low | Three authors independently. |
| 6 Duplicate extraction | low | Three authors independently. |
| 7 List of excluded studies with reasons (critical) | some concerns | Flow chart gives exclusion categories (67 excluded), not an itemised list. |
| 8 Description of included studies | low | Supplementary table of study characteristics. |
| 9 Risk of bias of individual studies (critical) | high | No study-level quality/RoB tool applied; only adjustment status noted. |
| 10 Funding of included studies | high | Not reported. |
| 11 Appropriate meta-analytic methods (critical) | low | Standard dose-response methods with random effects. |
| 12 Impact of RoB on results | high | Not assessed (no RoB tool). |
| 13 RoB considered in interpretation (critical) | some concerns | Confounding and small-study effects acknowledged; conclusions tempered. |
| 14 Heterogeneity explained | some concerns | Low heterogeneity mostly; no subgroup analyses possible. |
| 15 Publication bias (critical) | low | Egger tests and funnel plots reported; signal for fatal prostate cancer disclosed. |
| 16 Conflicts of interest of review | some concerns | No conflicts declared; funding not stated in retrieved text. |
Full-text review (25 October 2026): Added search/selection details, study counts per cancer, total prostate RR 1.00 (0.88-1.14), fatal prostate sensitivity RR 1.23 (0.97-1.55), I2 values, absence of study-level RoB and protocol, overlap with A-EGG-11; AMSTAR 2 itemised, overall some_concerns -> high.
9. Assessment of the statistical interpretation
The fatal prostate RR has a lower bound barely above 1, is sensitive to analytic assumptions and shows publication-bias signals; the total prostate cancer estimate is precisely null. The breast cancer signal is small (4-9%).
10. Relevance to the specific claim
11. Independent contrary findings
No total prostate cancer association.
12. Transferability to Germany and Europe
Moderate.
13. Overall methodological judgement
Weak, assumption-sensitive signal for fatal prostate cancer, no association with total prostate cancer, and small non-significant or marginal associations for breast and ovarian cancer. Insufficient to establish that eggs cause lethal prostate cancer.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | low |
| Risk of bias | high |
| Precision of results | low |
| 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
Larger prospective studies with repeated diet measures and aggressive-prostate-cancer endpoints; confounding by dietary pattern.
15. Linked fact checks
- Eating 2.5 or more eggs per week is associated with an 81% higher risk of lethal prostate cancer. – Studies with mixed or unclear results