Long-chain polyunsaturated omega-3 fatty acids (n-3 PUFAs) found in fish oil increase circulating levels of the hormone adiponectin, which may translate into benefits for insulin sensitivity, results of a meta-analysis suggest.
Taking fish oil supplements significantly increased adiponectin levels by 0.37 mcg/mL(P=0.02), Jason Wu, PhD, of Harvard, and colleagues reported in the Journal of Clinical Endocrinology and Metabolism.
Adiponectin, a known marker for insulin sensitivity, has been associated with lower type 2 diabetes and heart disease risk in previous studies. Animal models have shown that n-3 PUFAs improve circulating adiponectin levels and insulin sensitivity, but results have been inconsistent in humans.
“Although higher levels of adiponectin in the bloodstream have been linked to lower risk of diabetes and coronary heart disease, whether fish oil influences glucose metabolism and development of type 2 diabetes remains unclear,” Wu said.
To further evaluate n-3 PUFAs in humans, the researchers performed a meta-anlaysis of 14 randomized controlled clinical trials that examined the effects of either fish oil supplementation or dietary fish intake on adiponectin levels.
A total of 682 participants consumed fish oil and 641 took a placebo. Median fish oil dose was 1.3 g/day for a median treatment duration of 8 weeks.
Participants in the fish oil groups experienced a 0.37 mcg/mL increase in adiponectin levels. This translated into about a 3% lower diabetes incidence, the researchers determined.
The results also suggested the effect of fish oil on adiponectin differed substantially across the trials, suggesting that fish oil supplementation may have stronger influence on adiponectin in some populations and weaker effects in others.
For example, fish oils beneficial effects on adiponectin appeared to be stronger in higher quality trail and in those with younger or obese patients; however none of these factors were found to be statistically significant.
“[R]esults from our study suggest that higher intake of fish oil may moderately increase blood level of adiponectin, and these results support potential benefits of fish oil consumption on glucose control and fat cell metabolism,” Wu said in a statement.
The researchers warned that the subset of study participants in which the effect of direct fish intake were evaluated was small. Other limitations included statistical heterogeneity and evidence of publication bias.
More studies are needed to examine the effects of fish oil on other metabolic outcomes, such as inflammation, free fatty acids and insulin resistance.
- Wu JHY et al. “Effect of fish oil on circulating adiponectin: a systematic review and meta-analysis of randomized controlled trials.” J Clinical Endocrinol Metab 2013.