Cohort studyindependent cross-checkabstract checked★ key study I-CAN-127 in-depth review
Sugary drinks after breast cancer linked to higher death risk
Consumption of sugar-sweetened and artificially sweetened beverages and breast cancer survival.
Overview
Farvid MS et al.. Cancer 2021 · PMID 33945630 · DOI 10.1002/cncr.33461
Women who drank sugary drinks after a breast cancer diagnosis had a 31-35% higher risk of dying from breast cancer.
Does the study support the specific claim? No · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
SSB after breast cancer and death.
- How was the study done?
Prospective cohort.
- How many people, animals or samples were studied?
8,863 survivors.
- What was actually found?
Higher mortality with SSB; not with diet drinks.
- How large was the observed effect?
HR 1.35 (>3 servings/week).
- What do the results mean in everyday life?
Limiting sugary drinks after cancer is sensible.
- What are the study's limitations?
Observational.
- What does it say about Elawady's specific claim?
Contradicts the claim.
- Do the results apply to Germany and Europe?
High.
- What can explicitly not be concluded from this study?
Cause and effect.
Scientific in-depth review
1. Full reference
- Authors
- Farvid MS et al.
- Journal
- Cancer
- Year
- 2021
- Identifier
- PMID 33945630 DOI 10.1002/cncr.33461
- Verification
- verified – PubMed efetch 2026-10-26 + Crossref
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
AICR, Breast Cancer Research Foundation, NCI; one author with grants/fees from FHI Solutions, Arla Foods, Bayer outside the work (PubMed record)
2. Research question
Is post-diagnosis sugar-sweetened beverage (SSB) consumption associated with mortality after breast cancer?
3. Study design and population
- Study design
- Cohort study – Prospective cohort of breast cancer survivors (Nurses' Health Study I and II)
- Population
Women with stage I-III breast cancer
- Country
USA
- Period
Diagnoses 1980-2011; follow-up to 2014/2015 (median 11.5 years)
- Sample size
8,863 women; 2,482 deaths (1,050 from breast cancer)
- Inclusion and exclusion criteria
Stage I-III breast cancer with post-diagnosis FFQ
4. Methods and endpoints
- Exposure / intervention
Post-diagnosis SSB and artificially sweetened beverage intake
- Comparator
No SSB consumption
- Endpoints
Breast cancer-specific and all-cause mortality
- Statistical methods
Multivariable Cox regression adjusted incl. adiposity
5. Actual results
- Results
Breast cancer-specific mortality: >1-3 servings/week HR 1.31 (1.09-1.58); >3 servings/week HR 1.35 (1.12-1.62); p-trend .001. All-cause mortality: HR 1.21 (1.07-1.37) and 1.28 (1.13-1.45); p-trend .0001. Artificially sweetened beverages not associated.
- Absolute risks
not reported in abstract
- Authors' conclusion
Higher post-diagnosis SSB consumption was associated with higher breast cancer-specific and all-cause mortality.
6. Strengths
- Large, long follow-up
- Repeated diet measurement
- Adjustment for adiposity
- Dose-response
7. Weaknesses
- Observational; residual confounding
- Self-reported diet
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
Residual confounding (health behaviours) possible.
9. Assessment of the statistical interpretation
CIs log-symmetric (recalculated); dose-response trend.
10. Relevance to the specific claim
Most direct evidence on sugar intake in people who already have cancer: higher sugary-drink intake after diagnosis was linked to higher breast cancer mortality.
11. Independent contrary findings
Does not show that sugar 'feeds' tumours; mechanism unproven.
12. Transferability to Germany and Europe
High (US cohort).
13. Overall methodological judgement
Contradicts 'cancer patients need not fear sugar' at least for sugary drinks.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | moderate |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
RCT evidence.
15. Linked fact checks
- The idea that 'sugar feeds cancer' should be dropped: sugar feeds every cell (and microbe), so cancer patients need not fear sugar. – Studies contradicting or limiting the claim