Lipid-Lowering Therapy and Diabetes: Where Does Fish Oil Fit In?

Moderate intake of long chain omega-3 polyunsaturated fatty acids as a lipid-lowering strategy appears to have no effects on glucose regulation or insulin resistance.

For patients with elevated cholesterol, life-style changes are primary, but goals are often unattainable through these interventions alone.

Lipid-lowering drugs are used to augment lifestyle changes, and new guidelines (considered controversial by many) recommend treating patients by projected or calculated risk rather than lipid level. Such a change increases the number of adult Americans recommended for statin treatment from 43.2 million to 56 million. Lipid-lowering therapies clearly have benefits, including reducing adverse cardiovascular outcomes in many at-risk populations. Recently, some researchers have suggested that lipid-lowering drugs may affect glucose control and insulin resistance in varying degrees, depending on the class of agent.

The June 2014 issue of Cardiovascular Drugs and Therapy contains a comprehensive review of current thinking on this topic. The authors indicate that with metabolic syndrome and diabetes on the rise, understanding the relationship between lipid-lowering drugs, glycemic control and incident diabetes is critical.

Among the agents discussed in the article is supplemental fish oil, which contains long chain omega-3 polyunsaturated fatty acids (n-3 PUFA) predominantly in the form of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Dyslipidemic individuals treated with fish oil can reduce triglyceride levels by 20% to 50%, and may also increase HDL and LDL cholesterol levels slightly. A key reason for using fish oils to treat dyslipidemia is their possible anti-arrhythmic, antithrombotic, and anti-inflammatory effects on the cardiovascular system.

The authors review population-based studies that suggest fish and seafood intake may reduce the risk of impaired glucose tolerance and incidence of type 2 diabetes, although results are mixed. The authors indicate that study design variations, particularly in the amount, duration, and fatty acid composition of fish oils, account for the different findings. Older studies using very high doses of fish oils tended to report correlations between highest amount of fish consumed and risk for type 2 diabetes.

Several later meta-analyses found no significant association between fish oil supplementation and fasting glucose or HgbA1c in diabetic patients.

Fish oils may reverse, reduce, and prevent diet-induced insulin resistance. The authors indicate that substituting unsaturated fat for saturated fat may improve insulin sensitivity. They cover a variety of mechanisms by which insulin resistance may be reduced, including their known anti-inflammatory effect.

The authors conclude that moderate n-3 PUFA intake as a lipid-lowering strategy has been studied and appears to have no effects on glucose regulation or insulin resistance. The association with development of diabetes is weak at best.