A large, long-term population based study from Finland shows that men who get more than 5 grams of marine omega-3 fatty acids per day have 33% lower risk of developing type 2 diabetes compared with men who consume 3.6 grams or less.

The finding come from the Kuopio Ischaemic Heart Disease Risk Factor Study, a massive project that began in 1984. Dr. Jyrki Virtanen and colleagues at the Institute for Public Health and Clinical Nutrition analyzed data from 2,212 men between the ages of 42 and 60 years, who did not have diabetes back in 1984 or 1989, when they were enrolled in the study.

Over the ensuing years, the research team monitored EPA, DHA, docosapentaenoic acid (DPA) and alpha-linolenic acid (ALA) intake via periodic blood tests as well as patient self-recording of 4-day food intake at specific intervals. The researchers also periodically looked at hair mercury levels, an unfortunate surrogate marker for fish consumption.

They measured diabetes risk via fasting blood glucose levels, 2-hour oral glucose tolerance tests, and reexamination rebounds at 4, 11 and 20 years after enrollment. They also scoured subjects medical records for indicators of hospitalizations, medical visits, or prescriptions related to type 2 diabetes.

Over an average follow up period of 19.3 years, 422 of the men (19%) developed diabetes.

There was a marked difference in incidence based on omega-3 intake. Adjusting for other potential diabetes risk factors, men in the highest quartile for intake of EPA, DPA and DHA combined (ave of 5.33 g/d) had a 33% lower risk of diabetes than those in the lowest quartile (ave of 3.62 g/d).

Dr. Virtanen and his team found no correlation between ALA intake and diabetes risk. Likewise, they found no association between hair mercury levels—a recognized risk factor for cardiovascular disease—and diabetes.

The study was published last fall in the journal, Diabetes Care.