Vegetarian diets and cancer risk: pooled analysis of 1.8 million women and men in nine prospective studies on three continents

BACKGROUND: Vegetarian diets might influence cancer risk.

METHODS: We studied 1,645,555 meat eaters, 57,016 poultry eaters, 42,910 pescatarians, 63,147 vegetarians and 8849 vegans in 9 cohorts (UK, US, Taiwan, India). After a median 16 years follow up, incident cancers were: 4504 mouth and pharynx, 1308 oesophagus (squamous cell), 2105 oesophagus (adenocarcinoma), 3578 stomach, 30,528 colorectum, 2970 liver, 8030 pancreas, 3077 lung (never smokers), 61,368 breast, 11,220 endometrium, 8076 ovary, 45,946 prostate, 7193 kidney, 6869 bladder, 11,651 non-Hodgkin lymphoma, 4658 multiple myeloma and 7306 leukaemia. Multivariable Cox regression was used to estimate cohort-specific hazard ratios (HRs) and 95% confidence intervals (CIs), and the results were combined using meta-analysis.

RESULTS: Compared to meat eaters, poultry eaters had lower risk of prostate cancer (0.93, 0.88 – 0.98), pescatarians had lower risks of colorectal (0.85, 0.77–0.93), breast (0.93, 0.88–0.98) and kidney cancer (0.73, 0.58–0.93), vegetarians had lower risks of cancers of the pancreas (0.79, 0.65–0.97), breast (0.91, 0.86–0.97), prostate (0.88, 0.79–0.97), kidney (0.72, 0.57–0.92) and multiple myeloma (0.69, 0.51–0.93) but higher risk of squamous cell carcinoma of the oesophagus (1.93, 1.30–2.87), and vegans had higher risk of colorectal cancer (1.40, 1.12–1.75).

CONCLUSIONS: Vegetarian diets might influence risk for several cancers. The generalisability should be considered cautiously.