Supplementary long chain polyunsaturated fatty acids (PUFA) such as omega-3 have no effect on the prevention of diabetes or on glucose metabolism, a large meta-analysis commissioned by the World Health Organization (WHO) has found.

The investigators, for the PUFAH research group, searched Cochrane CENTRAL, Medline and Embase, up to April 2017 and ClinicalTrials.com and the WHO International Clinical Trials Registry Platform up to September 2016. All ongoing trials were then reassessed in December 2018 for suitability.

Randomised controlled trials (RCTs) assessing the effects of increasing alpha-linolenic acid, long chain omega-3, omega-6 or total PUFA on diabetes diagnosis and glucose metabolism of at least 24 weeks’ duration were deemed eligible.

A total of 83 RCTs, mainly assessing the effects of supplementary long chain omega-3 (66 trials), comprising 121,070 participants met the selection criteria. Participants were aged18 years or over and included those with diabetes, prediabetes or normal glucose metabolism. Acutely ill patients were excluded as well as pregnant women. The mean duration of the trials was 33 months, and the mean dose of omega-3 PUFA was 2.0 g.

Long chain omega-3 had little or no effect on the likelihood of a diagnosis of diabetes; relative risk (RR) 1.00 (95% CI: 0.85-1.17) or any other measures of glucose metabolism including HbA1c , fasting glucose, fasting insulin and insulin resistance (measured by HOMA-IR). All these measures had confidence intervals that crossed unity, suggesting no statistical effect.

At high doses of long chain omega-3 supplement (> 4.4 g/day) there was some suggestion of a worsening of glucose metabolism.

The study authors state:

‘No convincing evidence suggests that altering intakes of long chain omega-3, alpha-linolenic acid, omega-6, or total PUFA alters glucose metabolism or risk of diabetes. Supplemental long chain omega-3 should not be encouraged for prevention or treatment of diabetes.’

Patients often spend a lot of money on over the counter supplements and GPs may be able to advise them on this aspect of supplementation.

Dr Matthew Lockyer