Narrative reviewindependent cross-checkfull text checked I-DRY-17 in-depth review
Review: milk naturally contains hormones
Hormones in Dairy Foods and Their Impact on Public Health - A Narrative Review Article.
Overview
Malekinejad H et al.. Iran J Public Health 2015 · PMID 26258087
Milk contains small amounts of hormones (more in butter and cream than in milk); the authors raise a cancer concern but provide no new human outcome data.
Does the study support the specific claim? Partly · Methodological quality: very low
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Hormones in dairy.
- How was the study done?
Narrative review.
- How many people, animals or samples were studied?
n/a
- What was actually found?
Hormones present at ng/mL levels or below; highest oestrone and progesterone levels in butter and cream; several hormones poorly absorbed or rapidly degraded.
- How large was the observed effect?
n/a
- What do the results mean in everyday life?
Presence is not proof of harm.
- What are the study's limitations?
Narrative.
- What does it say about Elawady's specific claim?
Weak support.
- Do the results apply to Germany and Europe?
Moderate.
- What can explicitly not be concluded from this study?
Harm at usual intake; that butter, cream or ghee are lower in hormones than milk (the data suggest the opposite for fat-soluble steroids).
Scientific in-depth review
1. Full reference
- Authors
- Malekinejad H et al.
- Journal
- Iran J Public Health
- Year
- 2015
- Identifier
- PMID 26258087
- Verification
- verified – PubMed efetch 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- full text
- Conflicts of interest and funding
Authors declare no conflict of interest; no funding statement in the full text.
2. Research question
Which hormones occur in milk and dairy products, at what concentrations, how they are measured, and what their possible effects on human health are.
3. Study design and population
- Study design
- Narrative review – Narrative review (MEDLINE, ScienceDirect, Google Scholar, Web of Science; no date limits; no selection criteria) including the authors' own LC-MS/MS data on oestrogens in milk of pregnant and non-pregnant cows.
- Population
n/a
- Country
Iran (authors)
- Period
No date limits
- Sample size
n/a
- Inclusion and exclusion criteria
Not systematic; no eligibility criteria reported.
4. Methods and endpoints
- Exposure / intervention
Prolactin, IGF-1, prostaglandins, glucocorticoids, androgens, progesterone and oestrogens in cow's milk and dairy products.
- Comparator
n/a
- Endpoints
Hormone concentrations; hypothesised health effects (cancer, reproduction, growth). No human outcome data analysed.
- Statistical methods
None.
5. Actual results
- Results
Reported concentrations in cow's milk (ng/mL): prolactin 15.4 +/- 1, IGF-1 4 +/- 1, corticosteroids 14 +/- 4, progesterone 12 +/- 2, testosterone 0.09 +/- 0.03, oestrone 0.13, 17beta-oestradiol 0.02, oestriol 0.027. In a market-basket survey, total oestrone was highest in butter (1.47 ng/g), then cream 0.26, Gouda 0.17, yogurt 0.16, milk 0.13; 17beta-oestradiol <=0.02-0.03 ng/g in all products; progesterone highest in fat-rich products (e.g. butter 300 ng/g, cream 43 ng/g vs drinking milk 12 ng/mL in one cited study). Authors' own data: summed oestrogens 1639 ng/L in third-trimester milk vs 60 ng/L in first trimester (>27-fold). Review notes oral bioavailability of progesterone <10% due to first-pass metabolism, milk prolactin likely hydrolysed in adults, prostaglandins rapidly inactivated, androgens unlikely to have effects, and that IGF-1 bioavailability data are lacking; epidemiological evidence on milk and cancer described as 'very controversial'.
- Absolute risks
not applicable
- Authors' conclusion
Steroid hormones, especially oestrogens, in dairy foods are the main concern because of possible roles in breast and prostate cancer; even low doses may have effects, particularly in perinatal and pubertal periods; more sensitive analytical methods and clarification of health impact are needed.
6. Strengths
- Broad overview of hormone classes with tabulated concentrations
- Discusses bioavailability and metabolism, including arguments against systemic effects
- Includes authors' own LC-MS/MS data on pregnancy-dependent oestrogen levels
7. Weaknesses
- Narrative, non-systematic; no selection or appraisal of evidence
- Abstract conclusion ('important risk factor for various cancers') is stronger than the body text, which calls the cancer evidence 'very controversial' and notes low bioavailability for several hormones
- No dose-exposure comparison with endogenous human hormone production
- Some technical errors in the text (e.g. 'biologically inactive 17beta-estradiol')
- No DOI; regional journal
8. Risk of bias
- Orienting tool
- none applicable (narrative review); structured judgement of main validity threats
- 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
Single-reviewer structured judgement from full text; no standard tool fits a narrative review. Formal assessment would need two independent reviewers.
| Domain | Judgement | Rationale |
|---|---|---|
| Search and selection of evidence | high | Databases named but no search strategy, criteria or flow; selection unexplained. |
| Appraisal of cited evidence | high | No quality assessment; ecological correlations (e.g. Japan milk consumption vs prostate cancer) cited uncritically. |
| Consistency of conclusions with presented data | high | Concern-oriented conclusions not matched by the body text's own statements on low concentrations, low bioavailability and controversial epidemiology. |
| Conflict of interest | low | No conflicts declared. |
Full-text review (25 October 2026): Added concentration tables (e.g. milk oestrone 0.13 ng/mL, 17beta-oestradiol 0.02; butter oestrone 1.47 ng/g, progesterone up to 300 ng/g), authors' own pregnancy data (1639 vs 60 ng/L), bioavailability caveats, COI statement; noted that abstract conclusion is stronger than the body text. Structured judgement added; overall changed from not_assessable to high.
9. Assessment of the statistical interpretation
No statistics; concentrations are in the ng/mL to sub-ng/mL range and are not related to human exposure thresholds or health outcomes.
10. Relevance to the specific claim
Weak support for C-DRY-01 (hormones present).
11. Independent contrary findings
Epidemiological syntheses (I-DRY-12).
12. Transferability to Germany and Europe
Moderate.
13. Overall methodological judgement
Confirms that cow's milk naturally contains small amounts of hormones (higher in late pregnancy and in fat-rich products such as butter and cream); it provides no human outcome data, and its concern-oriented conclusion goes beyond its own evidence.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | very low |
| Risk of bias | high |
| Precision of results | not applicable |
| Directness | indirect |
| Reproducibility | unknown |
| Consistency with the overall evidence | unknown |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Human dose-response; comparison with endogenous hormone production; relevance of pregnant-cow milking practices to Egyptian supply.
15. Linked fact checks
- Milk is a 'substitute for blood' and carries every hormone, pesticide and antibiotic the animal received; therefore milk must be avoided. – Studies supporting the claim
- Fresh milk, yogurt (incl. laban rayeb, ayran, labneh) and white/cottage cheese are harmful and must be avoided, whereas aged cheeses (cheddar, mozzarella, romi), processed cheese triangles, cream (qeshta), butter and ghee are allowed. – Studies contradicting or limiting the claim