Systematic reviewcited by the Tayebat archivefull text checked★ key study A-DRY-14 in-depth review
Review: milk slightly raises IGF-1, which is linked to prostate cancer
Does milk intake promote prostate cancer initiation or progression via effects on insulin-like growth factors (IGFs)? A systematic review and meta-analysis.
Overview
Harrison S et al.. Cancer Causes Control 2017 · PMID 28361446 · DOI 10.1007/s10552-017-0883-1
IGF-I +0.10 SD per SD of milk; prostate cancer OR 1.09 per SD IGF-I.
Does the study support the specific claim? Yes · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Test the IGF pathway.
- How was the study done?
Systematic review of 172 studies.
- How many people, animals or samples were studied?
Humans and animals.
- What was actually found?
Moderate evidence for both links, but small effects; IGF-I not associated with advanced prostate cancer.
- How large was the observed effect?
OR 1.09 (1.03-1.16) per SD IGF-I.
- What do the results mean in everyday life?
A small, plausible mechanism.
- What are the study's limitations?
Inference across separate studies; milk-IGF effect only visually estimated; search to 2014.
- What does it say about Elawady's specific claim?
Supports the mechanism claim, not the size of harm.
- Do the results apply to Germany and Europe?
Moderate.
- What can explicitly not be concluded from this study?
That milk causes prostate cancer; the size of any milk-related risk via IGF-1.
Scientific in-depth review
1. Full reference
- Authors
- Harrison S, Lennon R, Holly J, Higgins JPT, Gardner M, Perks C, Gaunt T, Tan V, Borwick C, Emmet P, Jeffreys M, Northstone K, Rinaldi S, Thomas S, Turner SD, Pease A, Vilenchick V, Martin RM, Lewis SJ
- Journal
- Cancer Causes Control
- Year
- 2017
- Identifier
- PMID 28361446 DOI 10.1007/s10552-017-0883-1 · PMC5400803
- Verification
- verified – PubMed E-utilities efetch, 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- full text
- Conflicts of interest and funding
Funded by World Cancer Research Fund (RFA 2012/620); Wellcome Trust PhD studentship (102432/Z/13/Z); MRC Integrative Epidemiology Unit (MC_UU_12013/1, /2); Cancer Research UK programme grant (C18281/A19169); NIHR Bristol Nutritional BRU. No explicit competing-interest statement in the converted full text.
2. Research question
Does the milk-prostate cancer association operate via the IGF pathway?
3. Study design and population
- Study design
- Systematic review – Systematic review with two separate evidence streams (milk -> IGF; IGF -> prostate cancer) in humans and animals; MEDLINE, EMBASE, BIOSIS, CINAHL to March 2014, no language restriction; custom ROBINS-I/CASP-based risk-of-bias tool and GRADE; milk-IGF data synthesised only by albatross plots and Stouffer combined P values (no pooled effect size); IGF-PCa by random-effects meta-analysis per SD. Commissioned by WCRF as a case study for a mechanistic-review framework.
- Population
Humans (observational and experimental) and animals
- Country
Multinational
- Period
Literature search to March 2014
- Sample size
172 papers: 31 milk-IGF studies; 132 papers (125 studies) on IGF-PCa in humans, of which 71 unique studies meta-analysed (IGF-I 51 studies, 35,509 participants; IGFBP-3 39 studies, 32,214 participants); 10 animal studies; 11 human studies excluded for critical risk of bias.
- Inclusion and exclusion criteria
Original peer-reviewed articles incl. meeting abstracts; RCTs, cohort, case-control, non-randomised and case-series studies in humans and animal transgenic/xenograft models (not carcinogen-induced). Milk-IGF: cow's milk, dairy products or dairy protein vs serum/plasma IGF-I, IGF-II, IGFBP-1/-2/-3 (breast milk, colostrum, soy and formula excluded). IGF-PCa: circulating levels, expression or genetic variants vs prostate cancer incidence, progression or mortality. Studies with >=5-year age difference between cases and controls without age adjustment rated critical and excluded.
4. Methods and endpoints
- Exposure / intervention
Milk/dairy protein; circulating IGF-I, IGF-II, IGFBPs
- Comparator
Per SD increase in milk intake (1 SD roughly 200-350 mL) for IGF levels; per SD increase in IGF peptide for prostate cancer; genotypes vs reference genotype.
- Endpoints
IGF levels; prostate cancer risk/progression.
- Statistical methods
Albatross plots with visual estimation of standardised effect sizes and Stouffer's combined P values for milk-IGF; random- and fixed-effects meta-analysis (log OR per SD) for IGF-PCa with I2, Egger/Begg, subgroups (prospective vs retrospective, PSA vs clinically detected, advanced PCa); GRADE per exposure-outcome pair.
5. Actual results
- Results
Milk-IGF (visual estimate, not pooled): IGF-I +0.10 SD per 1 SD milk (range 0.05-0.25), 29 of 31 data points positive, combined P = 2.2 x 10^-27; IGFBP-3 +0.05 SD (range 0.00-0.10), combined P = 4.3 x 10^-15; IGF-II <0.05 SD; IGFBP-1 none; IGFBP-2 slight decrease. Largest effects in small short-term trials in children (Mongolian children +23% IGF-I after 1 month of milk; Danish 8-year-olds +19% after 7 days of 1.5 L skimmed milk/day). Childhood milk exposure studies with adult IGF follow-up showed slightly negative associations. IGF-PCa per SD: IGF-I OR 1.09 (1.03-1.16; 51 studies; I2 0.86), prospective 1.07 (1.02-1.12; 16 studies), retrospective 1.12 (1.01-1.23); advanced PCa IGF-I 1.04 (0.94-1.14; 12 studies); IGFBP-3 0.90 (0.83-0.98) random effects but fixed effect 1.02 (1.00-1.04) and prospective 1.02 (0.99-1.05), Egger P = 0.02; IGF-II 1.07 (0.97-1.18); IGFBP-1 1.02 (0.77-1.34); IGFBP-2 1.07 (0.91-1.25). IGFBP-3 -202A/C: C/C vs A/A 1.51 (1.03-2.21), A/C vs A/A 1.22 (0.84-1.79); IGF-I (CA)n repeats null. Animal studies inconsistent (very low GRADE). GRADE: moderate evidence milk increases IGF-I and that IGF-I increases PCa risk; other links low or very low.
- Absolute risks
not reported in full text
- Authors' conclusion
Combined human, animal and genetic evidence supports a role of the IGF pathway, in particular IGF-I, in explaining the association between milk and prostate cancer; however, even for IGF-I the evidence that it increases prostate cancer risk 'is not strong' and further high-quality studies are needed.
6. Strengths
- Comprehensive multi-database search without language restriction; duplicate screening and extraction
- Explicit risk-of-bias assessment with exclusion of critical-risk studies, and GRADE per link
- Separation of prospective vs retrospective studies to address reverse causation
- Public/charitable funding
7. Weaknesses
- Milk-IGF effect size is a visual estimate from albatross plots, not a pooled estimate; heterogeneous exposures (milk, dairy products, dairy protein)
- Largest milk-IGF effects come from very small, short-term trials in children with large doses
- Mediation not tested directly: the two links are combined qualitatively; no study links milk, IGF and PCa in the same people
- High heterogeneity for IGF-PCa (I2 66-88%); IGF-I not associated with advanced PCa; IGFBP-3 protective association driven by retrospective studies
- Search ended March 2014; no registered protocol reported; IGF-I association smaller than in earlier meta-analysis
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
- some concerns
- Rationale
Simplified single-reviewer AMSTAR 2 from full text: methodologically strong review whose main limitation is the indirect, non-pooled milk-IGF synthesis and qualitative mediation inference. A formal assessment needs two independent reviewers.
| Domain | Judgement | Rationale |
|---|---|---|
| Item 2 protocol established a priori (critical) | some concerns | Part of a pre-specified WCRF framework, but no registered protocol cited. |
| Item 4 comprehensive search (critical) | low | Four databases, no language restriction, search terms in supplement. |
| Items 5-6 duplicate selection and extraction | low | Two independent assessors for screening; duplicate extraction. |
| Item 7 list of excluded studies (critical) | some concerns | Flow diagram and critical-RoB exclusions referenced; full excluded list with reasons not evident in main text. |
| Item 9 risk of bias of included studies (critical) | low | Custom ROBINS-I/CASP-based tool applied to all studies; critical-RoB studies excluded. |
| Item 11 appropriate synthesis (critical) | some concerns | Appropriate random-effects for IGF-PCa; milk-IGF magnitude only visually estimated; mediation inferred across separate bodies of evidence. |
| Item 13 risk of bias considered in interpretation (critical) | low | GRADE used; authors state evidence for IGF-I-PCa is not strong. |
| Item 14 heterogeneity | low | I2 reported and explored by design and detection subgroups. |
| Item 15 publication bias (critical) | low | Funnel plots, Egger/Begg reported; small-study effects found for IGFBP-3. |
| Item 16 conflicts of interest | some concerns | Funding fully reported; no explicit COI declaration found in converted text. |
Full-text review (25 October 2026): Added search dates, study counts per analysis, that the milk-IGF effect is a visual albatross-plot estimate (range 0.05-0.25 SD), prospective IGF-I OR 1.07 (1.02-1.12), null advanced-PCa association (1.04, 0.94-1.14), IGFBP-3 protection limited to retrospective/random-effects, GRADE ratings and authors' statement that IGF-I-PCa evidence is 'not strong'; full funding list. Structured AMSTAR 2 added; overall unchanged (some_concerns). use_by_archive refined.
9. Assessment of the statistical interpretation
Both links are small: about 0.10 SD higher IGF-I per ~200-350 mL/day more milk (visual estimate), and 7-9% higher PCa odds per SD of IGF-I (no association with advanced PCa). Chaining them implies a very small milk-attributable risk change via IGF-I; neither link is causal proof and no absolute risks are given.
10. Relevance to the specific claim
Core for C-DRY-06; supporting C-DRY-04.
11. Independent contrary findings
Small magnitudes.
12. Transferability to Germany and Europe
Moderate.
13. Overall methodological judgement
Well-conducted mechanistic review supporting IGF-I as a plausible but small and not firmly established mediator of the milk-prostate cancer association; authors themselves rate the evidence as moderate at best and the IGF-I-PCa evidence as 'not strong'.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | some concerns |
| Precision of results | moderate |
| Directness | indirect |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | mixed |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | essentially correct but incomplete |
14. Open questions
Mendelian-randomisation and direct mediation analyses; whether adult (not childhood) milk intake drives the effect; advanced/lethal PCa; updated search after 2014.
15. Linked fact checks
- Dairy consumption increases prostate cancer risk (7% per 400 g/day; 34% for more than 2.5 servings/day). – Studies supporting the claim
- Milk intake raises circulating IGF-1, and higher IGF-1 increases prostate cancer risk; this is the mechanism behind the dairy-prostate cancer link ('the same hormone that makes a calf grow'). – Studies supporting the claim
Use by the Tayebat archive
Note: according to the archive, the studies were compiled by the archive operators. Whether Dr. Elawady himself cited this study is not established.
- What the archive says about the study
Milk intake raises circulating IGF-1, and higher IGF-1 in turn increases prostate cancer risk; 'the very hormone that lets a calf double in size'.
- A. What was actually studied?
Milk-IGF and IGF-prostate cancer links.
- B. What did the authors find?
Moderate (GRADE) evidence that milk raises IGF-I by about 0.10 SD per SD of intake (visual estimate) and that IGF-I is associated with prostate cancer (OR 1.09 per SD; prospective 1.07); no association with advanced prostate cancer (1.04, 0.94-1.14).
- C. What conclusions do the authors themselves draw?
IGF-I is a potential mechanism; evidence that IGF-I increases prostate cancer risk is not strong; more high-quality studies needed.
- D. What does the archive derive from it?
Presents IGF-1 as established mechanism and links to calf growth.
- E. Is this derivation scientifically justified?
Direction correct, but the archive presents as established a mechanism the authors rate as moderate-certainty and 'not strong'; effects are small, the milk-IGF magnitude is a visual estimate, the largest IGF rises were in children given large amounts of milk for days to weeks, and the 'calf growth' analogy is rhetorical.
- Adequacy of the interpretation (by the archive)
- essentially correct but incomplete