People with type 2 diabetes are known to be at increased risk of cardiovascular disease (such as heart attack or stroke). Type 2 diabetes mellitus is the fourth leading cause of death in developed countries with a two fold excess mortality and a two to four fold increased risk of coronary heart disease and stroke. The typical dyslipidemia (abnormality in blood lipids) associated with type 2 diabetes is a combination of hypertriglyceridemia (high levels of fats (triglycerides) in the blood), low levels of HDL (high density lipoprotein) cholesterol and abnormal LDL (low density lipoprotein) composition. Low levels of HDL cholesterol and high levels of LDL cholesterol are associated with an increased risk of cardiovascular disease, while the raised levels of triglycerides are less clearly linked to an increased risk of cardiovascular disease. Several pharmacologic approaches have been used to treat diabetic dyslipidemia and standard dietary approaches focus on restriction of saturated fat and limitation of simple carbohydrate and alcohol intake. In the late 1980s, several investigators reported on the use of dietary supplementation with fish oil as a means of treating diabetic dyslipidemia. Dietary fats and oils from different sources differ considerably in their fatty acid composition. Animal fat is rich in saturated fatty acids, vegetable and marine oils are rich in polyunsaturated fatty acids. Most fish oils are of the so-called omega-3 variety (omega-3 polyunsaturated fatty acids (PUFAs)).
We identified 23 randomised trials (maximum duration of eight months) including 1075 people in which omega-3 PUFA was compared to a vegetable oil or placebo. None of the trials looked at cardiovascular endpoints in cardiovascular disease or death as an outcome measure.
The review shows that although some types of fat in the blood are reduced through omega-3 supplementation, others including LDL cholesterol (which may promote heart disease) were increased. Control of blood sugar levels was not affected by the treatment. There were no other adverse effects of the interventions noted. Clinical outcome trials of sufficient duration are required to establish conclusively the role of omega-3 PUFA in type 2 diabetes but our results do not suggest a major harmful effect on the balance of blood fats and confirm that it has no adverse affect on blood sugar control. —Cochrane 2009