Intakes of Fish and Long-chain n-3 Polyunsaturated Fatty Acid Supplements During Pregnancy and Subsequent Risk of Type 2 Diabetes in a Large Prospective Cohort Study of Norwegian Women

OBJECTIVE To investigate associations between intakes of total fish, lean fish, fatty fish, and long chain n-3 polyunsaturated fatty acid (LCn-3PUFA) supplements and risk of type 2 diabetes in women after pregnancy. Furthermore, to compare the estimated intakes of methylmercury (MeHg) and sum of dioxins and dioxin-like polychlorinated biphenyls (dl-PCBs) to tolerable weekly intakes (TWI). RESEARCH DESIGN AND METHODS Women free of diabetes at baseline (n=60,831) who participated in the population-based Norwegian Mother, Father, and Child Cohort study (MoBa) were prospectively evaluated for incident type 2 diabetes identified through medication usage more than 90 days after delivery ascertained by the Norwegian Prescription Database. Dietary intake data was obtained by a validated 255-item food frequency questionnaire (FFQ) which assessed habitual diet during the first four to five months of pregnancy. MeHg and sum of dioxins and dl-PCBs intakes were derived using a contaminant database and the FFQ. RESULTS Median (IQR) age was 31 (27, 34) years at time of delivery and follow-up time was 7.5 (6.5, 8.5) years. Type 2 diabetes occurred in 683 (1.1%) participants. Multivariable Cox regression analyses identified lower risk of type 2 diabetes with increasing energy-adjusted lean fish intake per 25 g/1000 kcal (HR 0.71, 95% CI 0.53-0.95, p=0.022). However, in stratified analyses, a lower risk was found only in women with pre-pregnancy BMI ≥25 kg/m2. There were no associations between intake of total fish, fatty fish, or LCn-3PUFA supplements and type 2 diabetes. MeHg intake was low, but the sum of dioxins and dl-PCBs (pg TEQ/kg bw/wk) exceeded the TWI set by the European Food and Safety Authority (EFSA) for the majority of participants. CONCLUSIONS Intake of lean fish, but not fatty fish or LCn-3PUFA supplements, was associated with lower risk of pharmacologically treated type 2 diabetes in Norwegian women who were overweight or obese. Fatty fish, which contain dioxins and dl-PCBs, did not increase the risk of type 2 diabetes, but the exceedance of the EFSA TWI for dioxins and dl-PCBs is a health concern.