Omega-3s may help lower risk of type 2 diabetes

High concentrations of serum long-chain omega-3 fatty acids may help reduce the risk of type 2 diabetes, according to a University of Eastern Finland study published recently in Diabetes Care. The sources of these fatty acids are fish and fish oils.

“As with the recommendations for cardiovascular disease prevention, it may be beneficial to have a few fish meals per week, preferably with fatty fish, in order to reduce also the risk of type 2 diabetes,” said Jyrki Virtanen, PhD, Docent in Nutritional Epidemiology, University of Eastern Finland Institute of Public Health and Clinical Nutrition. “There is much data about the beneficial impact of fish consumption in the prevention of cardiovascular diseases. This study suggests that fish consumption may be helpful in reducing the risk of type 2 diabetes, also.”

Type 2 diabetes is prevalent in Finland and the numbers are constantly rising, so there’s a need for new ways to prevent the disease, said Virtanen.

The University of Eastern Finland’s ongoing Kuopio Ischaemic Heart Disease (KIHD) Risk Factor Study determined the serum omega-3 fatty acid concentrations of 2,212 men between aged 42 and 60 years at the onset of the study, in 1984 to 1989.

Serum long-chain omega-3 polyunsaturated fatty acid (PUFA) concentrations have been associated with several cardiovascular disease outcomes, according to Virtanen.

“Also in our KIHD study population, and the results from other study populations regarding fish or omega-3 PUFAs and type 2 diabetes risk have been mixed, so we wanted to investigate the association in our KIHD cohort,” he said.

“Also, there is very little information about the association between the environmental contaminants in fish and risk of type 2 diabetes,” he said. “We have previously shown that exposure to methylmercury, a major source of which is fish, increased the risk of cardiovascular diseases and also attenuated the benefits of the serum omega-3 PUFAs on the risk in the KIHD study population. Therefore, we also wanted to investigate whether it could influence the risk of type 2 diabetes also.”

Virtanen and colleagues assessed serum omega-3 PUFA concentrations and hair mercury at baseline from 1984 to 1989. Type 2 diabetes incidence during the follow-up was assessed by self-administered questionnaires and glucose tolerance tests with blood glucose measurements at 4, 11, and 20 years after the baseline, and by record linkage to hospital discharge registry and reimbursement register on diabetes medication expenses.

Few prior studies have used an objective biomarker (ie, circulating omega-3 PUFAs) as an exposure to investigate the association between fish consumption and risk of type 2 diabetes, which may partly explain the diverse findings from the previous studies, according to Virtanen.

“Circulating PUFAs offer an objective biomarker for exposure, so they don’t rely on memory like dietary assessment methods,” Virtanen said. “This reduces random error that is always present in studies using dietary assessment methods, such as food frequency questionnaires. Random error can attenuate associations in dietary studies and thus could explain null findings in some studies.”

The main finding was that serum long-chain omega-3 PUFA concentration, an objective biomarker of fish and long-chain omega-3 PUFA intake, was associated with a lower risk of incident type 2 diabetes during the average follow-up of 19.3 years in middle-aged and older men from Eastern Finland. The risk was 33% lower in the highest versus the lowest quartile after adjustment for potential confounders.

In contrast, hair mercury, a marker for long-term exposure to mercury, was not associated with the risk. Previously in this study population, high hair mercury content has been associated with higher risk of cardiovascular diseases and attenuation of the beneficial impact of long-chain omega-3 PUFA on the risk.

Also, the researchers did not find associations with the intermediate-chain length omega-3 PUFA alpha-linolenic acid, either, which is a plant-based omega-3 PUFA.

“This suggests that the findings were specific to the long-chain omega-3 PUFAs from fish,” Virtanen said.