Aims/hypothesis  

To determine the effects of marine-derived n-3 polyunsaturated fatty acids (PUFA) on established and emerging lipid and lipoprotein cardiovascular risk markers in patients with type 2 diabetes.

Materials and methods  

We performed a systematic review and meta-analysis of randomised controlled trials comparing dietary or non-dietary intake of n-3 PUFA with placebo in patients with type 2 diabetes by searching databases from 1966 to December 2006. Changes in the following variables were recorded triacylglycerol; total cholesterol; HDL, LDL and VLDL and their subfractions; lipid ratios; apolipoproteins; and cholesterol particle sizes.

Results  

There were 23 trials on non-dietary supplementation, involving 1,075 subjects with a mean treatment duration of 8.9 weeks, with sufficient data to permit pooling. Compared with placebo, n-3 PUFA had a statistically significant effect on four outcomes, reducing levels of (1) triacylglycerol (18 trials, 969 subjects) by 25% (mean 0.45 mmol/l; 95% CI −0.58 to −0.32; p < 0.00001); (2) VLDL-cholesterol (7 trials, 238 subjects) by 36% (0.07 mmol/l; 95% CI −0.13 to 0.00; p = 0.04); and (3) VLDL-triacylglycerol (6 trials, 178 subjects) by 39.7% (0.44 mmol/l; 95% CI −0.83 to −0.05; p = 0.03); while slightly increasing LDL (16 trials, 565 subjects) by 5.7% (0.11 mmol/l; 95% CI 0.00 to 0.22; p = 0.05). There were no significant effects on total cholesterol, apolipoproteins, lipid subfractions or ratios.

Conclusions/interpretation  

In addition to recognised triacylglycerol-lowering effects, n-3 PUFA supplementation decreases VLDL-cholesterol and VLDL-triacylglycerol, but may have an adverse effect on LDL-cholesterol. Larger and longer term clinical trials are required to conclusively establish the effect of n-3 PUFA on cardiovascular risk markers and outcomes in type 2 diabetic patients.