Abstract
BackgroundThe relationship between long-chain omega-3 (LCn3), alpha-linolenic acid (ALA), omega-6 and total polyunsaturated fatty acid (PUFA) intakes and cancer risk is unclear.MethodsWe searched Medline, Embase, CENTRAL and trials registries for RCTs comparing higher with lower LCn3, ALA, omega-6 and/or total PUFA, that assessed cancers over ≥12 months. Random-effects meta-analyses, sensitivity analyses, subgrouping, risk of bias and GRADE were used.ResultsWe included 47 RCTs (108,194 participants). Increasing LCn3 has little or no effect on cancer diagnosis (RR1.02, 95% CI 0.98–1.07), cancer death (RR0.97, 95% CI 0.90–1.06) or breast cancer diagnosis (RR1.03, 95% CI 0.89–1.20); increasing ALA has little or no effect on cancer death (all high/moderate-quality evidence). Increasing LCn3 (NNTH 334, RR1.10, 95% CI 0.97–1.24) and ALA (NNTH 334, RR1.30, 95% CI 0.72–2.32) may slightly increase prostate cancer risk; increasing total PUFA may slightly increase risk of cancer diagnosis (NNTH 125, RR1.19, 95% CI 0.99–1.42) and cancer death (NNTH 500, RR1.10, 95% CI 0.48–2.49) but total PUFA doses were very high in some trials.ConclusionsThe most extensive systematic review to assess the effects of increasing PUFAs on cancer risk found increasing total PUFA may very slightly increase cancer risk, offset by small protective effects on cardiovascular diseases.
Highlights
Cancer is a leading cause of morbidity and mortality worldwide with approximately 17 million new cases and 9.6 million cancer-related deaths in 2018 1
Inclusion criteria We included randomised controlled trials (RCTs) that compared higher versus lower long-chain omega-3 (LCn3), alpha-linolenic acid (ALA), omega-6 and/or total polyunsaturated fatty acid (PUFA) in adults aged at least 18 years, who were not pregnant or seriously ill
Where we found a suggested effect we quantified the effect using number needed to treat for an additional benefit (NNTB) or number needed to treat to cause an additional harm (NNTH).[49]
Summary
Cancer is a leading cause of morbidity and mortality worldwide with approximately 17 million new cases and 9.6 million cancer-related deaths in 2018 1. Reducing dietary fat (including PUFAs) appears to result in lower weight in adults 8, so lower PUFA intake (as part of general fat reduction) could offer protective effects against those cancers that are associated with overweight. These mechanisms suggest that omega-3 may be protective, and omega-6 and total PUFA may exacerbate cancer risk. The relationship between long-chain omega-3 (LCn3), alpha-linolenic acid (ALA), omega-6 and total polyunsaturated fatty acid (PUFA) intakes and cancer risk is unclear
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