Does taking omega-3 help you stay healthy for longer?

Omega-3 reliably lowers triglycerides (a blood fat that raises heart risk at high levels) by around 15%. This is the strongest and most consistent effect of omega-3 supplementation. But lower triglycerides does not automatically mean you will live longer.

A large Cochrane meta-analysis of 45 randomised studies with nearly 144,000 participants found no measurable difference in the risk of premature death (risk ratio 0.97). For the risk of dying from cardiovascular disease there was a small effect: the risk ratio was 0.92, which is statistically significant but modest. For strokes there was no demonstrable benefit at all, and the confidence interval did not even fully exclude a slightly increased risk.

In people who already have heart disease, the picture is somewhat more favourable. Based on large randomised studies, the American Heart Association concludes that omega-3 offers the greatest benefit precisely in that group, rather than in healthy people taking supplements as a preventive measure.

On biological ageing the results are mixed. A trial in 777 older adults found, after three years of omega-3 use, a small slowdown in biological age as measured by a DNA methylation test: a difference of a few months. That sounds promising, but it was not a pre-planned measurement and its relevance to actual health or lifespan is unknown. Another large randomised study found no effect at all on telomere length, a different marker of cellular ageing.

An observational study in the UK Biobank cohort of more than 427,000 people showed that participants who took fish oil had lower mortality (risk ratio 0.87 for total mortality). But this is not an experiment: people who take supplements generally also live more healthily in other ways. Causality has therefore not been demonstrated.