Published: May 22, 2013 | Updated: May 22, 2013

By Kristina Fiore , Staff Writer, MedPage Today

Image from MedPageToday

Action Points

• In this study, the long-chain fatty acids found in fish oil moderately increased levels of the hormone adiponectin, which could have protective effects on insulin sensitivity.
• Note that the findings suggest the need for additional studies looking at the effects of fish oil supplementation on other metabolic outcomes such as inflammation, free fatty acids, and insulin resistance.

The long-chain fatty acids found in fish oil moderately increased levels of the hormone adiponectin, which could have protective effects on insulin sensitivity.

In a meta-analysis, taking fish oil supplements significantly increased circulating adiponectin levels by 0.37 mcg/mL (P=0.02), Jason Wu, PhD, of Harvard, and colleagues reported online in the Journal of Clinical Endocrinology and Metabolism.

“While prior animal studies found fish oil increased circulating adiponectin, whether similar effects apply in humans is not established,” Wu said in a statement. “By reviewing evidence from existing randomized clinical trials, we found that fish oil supplementation caused modest increases in adiponectin in the blood of humans.”

Adiponectin is a known marker for insulin sensitivity, and has been associated with a lower risk of type 2 diabetes and heart disease in prospective studies.

Long-chain polyunsaturated omega-3 fatty acids (n-3 PUFA) improve insulin sensitivity in animal models, and they’ve been shown to increase levels of adiponectin in adipocytes in both in vitroand animal models.

But those findings have been inconsistent in humans.

So Wu and colleagues conducted a systematic review and meta-analysis of randomized controlled trials that evaluated either fish oil supplementation or dietary intake of fish that evaluated adiponectin as an outcome.

Overall, they looked at 14 trials in which 682 patients had been treated with fish oil and 641 had taken placebo, typically either sunflower or olive oil. The median dose of fish oil was 1.3 g/day and the median duration of treatment was 8 weeks.

Wu and colleagues found that fish oil significantly increased adiponectin levels by 0.37 mcg/mL (P=0.02), which they calculated would translate to about a 3% lower incidence of diabetes.

They noted that the effects of fish oil intake on adiponectin appeared to be stronger in trials of higher quality and in trials with younger or obese patients — but none of these interactions were statistically significant.

They also warned that they found statistical heterogeneity as well as evidence of publication bias.

Also, only two trial arms evaluated the effects of direct fish intake, and they revealed in a pooled analysis that there was no significant effect on adiponectin levels.

Nonetheless, Wu said the findings have significant implications for further exploration of fish oil’s effects on adiponectin.

“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 in the statement. “However, results from our study suggest that higher intake of fish oil may moderately increase blood levels of adiponectin, and these results support potential benefits of fish oil consumption on glucose control and fat cell metabolism.”

The findings also highlight the need for additional studies looking at the effects of fish oil supplementation on other metabolic outcomes such as inflammation, free fatty acids, and insulin resistance, the researchers wrote.

The study was limited by heterogeneity and by the quality of individual studies included.

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