Omega-3, omega-6 and total dietary polyunsaturated fat on cancer incidence: systematic review and meta-analysis of randomised trials

Background: 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. Methods: We 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. Results: We 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. Conclusions: The 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

Omega-3, omega-6 and polyunsaturated fat for cognition: systematic review & meta-analysis of randomised trials

Objectives: Neurocognitive function may be influenced by polyunsaturated fat intake. Many older adults consume omega-3 supplements hoping to prevent cognitive decline. We assessed effects of increasing omega-3, omega-6, or total polyunsaturated fats on new neurocognitive illness and cognition. Design and inclusion criteria: We carried out a systematic review and meta-analysis of randomized controlled trials (RCTs) in adults, with duration ≥24 weeks, assessing effects of higher vs lower omega-3, omega-6, or total polyunsaturated fats and outcomes: new neurocognitive illness, newly impaired cognition, and/or continuous measures of cognition.  Methods: We searched MEDLINE, Embase, Cochrane CENTRAL, and trials registers (final update of ongoing trials December 2018). We duplicated screening, data extraction, and risk of bias assessment. Neurocognitive measures were grouped to enable random effects meta-analysis. GRADE assessment, sensitivity analyses, and subgrouping by dose, duration, type of intervention, and replacement were used to interrogate our findings.  Results: Searches generated 37,810 hits, from which we included 38 RCTs (41 comparisons, 49,757 participants). Meta-analysis suggested no or very little effect of long-chain omega-3 on new neurocognitive illness [risk ratio (RR) 0.98, 95% confidence interval (CI) 0.87-1.10, 6 RCTs, 33,496 participants, I 2 36%), new cognitive impairment (RR 0.99, 95% CI 0.92-1.06, 5 RCTs, 33,296 participants, I 2 0%) or global cognition assessed using the Mini-Mental State Examination (MD 0.10, 95% CI 0.03-0.16, 13 RCTs, 14,851 participants, I 2 0%), all moderate-quality evidence. Effects did not differ with sensitivity analyses, and we found no differential effects by dose, duration, intervention type, or replacement. Effects of increasing α-linolenic acid, omega-6, or total PUFA were unclear.  Conclusions: This extensive trial data set enabled assessment of effects on neurocognitive illness and cognitive decline not previously adequately assessed. Long-chain omega-3 probably has little or no effect on new neurocognitive outcomes or cognitive impairment. Implications: Long-chain omega-3 supplements do not help older adults protect against cognitive decline