Dietary Fish Linked to Lower Risk for Type 2 Diabetes in Men

Akiko Nanri, from the Department of Epidemiology and Prevention, International Clinical Research Center, National Center for Global Health and Medicine in Tokyo, Japan, and colleagues write, "Although fish intake can improve glucose metabolism, results of some prospective studies in Western populations suggest potential adverse effects of environmental contaminants in fish on type 2 diabetes risk."  

"However, data from populations with high fish consumption are scarce. We prospectively investigated the association between fish intake and type 2 diabetes risk in Japanese adults." 

The study cohort consisted of 22,921 men and 29,759 women 45 to 75 years old with no history of diabetes. Participants completed a questionnaire of the second survey for the Japan Public Health Center–based Prospective Study and a 147-item food-frequency questionnaire. Logistic regression allowed estimation of odds ratios (ORs) for self-reported, physician-diagnosed type 2 diabetes during a 5-year period. 

Of 971 new cases of type 2 diabetes self-reported during the 5-year period, 572 were in men, and 399 were in women. Fish intake in men was significantly associated with a reduced risk for type 2 diabetes. For the highest vs. the lowest quartile of intake, multivariable-adjusted ORs of type 2 diabetes were 0.73 for total fish and seafood (95% confidence interval [CI], 0.54 - 1.00; P for trend = .04), and 0.68 for small and medium fish, including horse mackerel and sardine, saury and mackerel, and eel (95% CI, 0.50 - 0.92; P for trend = .016). For each category, further analysis based on the fat content of fish did not reveal any significant association.                                                                    

Fish consumption in women was not significantly related to a risk for type 2 diabetes.

"In a population with high fish and seafood intake, fish consumption was associated with a lower risk of type 2 diabetes in men but not in women," the study authors write. "We speculated that the null finding in women in the current study may have been due to their relatively high proportion of body fat mass, which may have been responsible for higher levels of accumulation of fat-soluble chemicals, which negated the benefit of fish intake on glucose metabolism." 

Limitations of this study include lack of dietary intake data by cooking method, lack of information other than the questionnaire for a diagnosis of type 2 diabetes, exclusion of a large number of participants because of missing data, and possible selection bias. Other limitations were assessment of dietary intakes at only 1 time point, lack of information about potential toxins from fish, and possible unmeasured and residual confounding. 

"The current study provides evidence to support a protective role of fish intake against type 2 diabetes," the study authors conclude. "Biological mechanisms underlying the inverse association between fish intake and type 2 diabetes need to be clarified."

Am J Clin Nutr. July 20, 2011