Lean fish intake may be associated with a lower risk for pharmacologically-treated type 2 diabetes (T2D) in women following pregnancy, according to research published in Diabetes Care; however, secondary findings showing higher levels of environmental toxins in the body potentially due to eating contaminated fish is a concern.
Researchers prospectively evaluated data from a population-based Norwegian Mother, Father, and Child Cohort Study (MoBa) to determine the associations among total, lean, and fatty fish intake, long-chain n-3-polyunsaturated fatty acid (LCn-3PUFA) supplementation, and T2D risk in women following pregnancy.
The MoBa cohort included 114,500 children, 95,200 mothers, and 75,200 fathers. Pregnant women were recruited between 1999 and 2008, ahead of their 18 weeks’ gestational ultrasound; 41% consented to participation.
A semi-quantitative food-frequency questionnaire was used to collect information on dietary intake, and a 4-day weighted food diary was used to validate the questionnaire. Motion sensors were utilized to determine energy expenditure, and 24-hour urine and blood samples were collected to mark food and nutrients.
The total cohort included 60,831 women who were eligible and included in analyses. Median age at the time of delivery was 31 years (interquartile range [IQR], 27-34 years). Median pregnancy weight was 65 kg and prepregnancy body mass index (BMI) was 23.1 kg/m2; 68.1% of participants had a BMI <25 kg/m2.
Among participants, median absolute intake of total fish, lean fish, and fatty fish was 33.3 g/d, 18.4 g/d, and 7.5 g/d, respectively. Median energy-adjusted intake was 14.9 g/1000 kcal/d, 8.1 g/1000 kcal/d, and 3.4 g/1000 kcal/d, respectively.
Energy-adjusted total fish intake quintiles were positively associated with age, maternal physical activity, and prepregnancy education level; quintiles were inversely associated with daily prepregnancy smoking and preeclampsia.
Total fish intake was also positively associated with the intake of mutton, poultry, bread, cereal, pasta, eggs, fruits, vegetables, nuts, fiber, polyunsaturated fat, and LCn-3PUFA from both food and supplements. Conversely, total fish intake was inversely associated with meat consumption in general, as well as carbohydrates, added sugar, saturated fat, and monounsaturated fat. Findings were similar when total fish intake was evaluated as absolute fish intake.
Intake levels of the LCn-3PUFA supplement were positively associated with the intake of total energy, all energy-adjusted fish categories — excluding shellfish — milk and dairy, bread, cereal, pasta, eggs, fruits and vegetables, nuts, fiber, and protein. An inverse association with meat in general — excluding mutton and poultry — was noted, as well as with added sugar and total fat.
A subgroup of 591 participants with gestational diabetes was identified, of whom 32% (n=191) developed T2D during the follow-up. Over a maximum 10-year and median 7.5-year follow-up, a total of 683 participants from the cohort developed pharmacologically-treated T2D.
Results of Cox regression analyses showed that across models, the risk for T2D was lower with increased energy-adjusted fish intake (25 g/1000 kcal; hazard ratio [HR], 0.71; 95% CI, 0.53-.095).
No significant associations were noted in Cox models where fish intake was evaluated as absolute intake.
Results of Cox regression analyses of quintiles of energy-adjusted fish intake showed a lower risk for T2D with lean fish intake in quintiles 2, 3, and 5 vs quintile 1. The strongest association was noted for quintile 3 (HR, 0.69; 95% CI, 0.55-0.88).
Results of analyses stratified by prepregnancy BMI categories (<25 and ≥25 kg/m2) were also studied; a lower T2D risk was observed with increased energy-adjusted lean fish intake (25 g/100 kcal) in the group with BMI ≥25 kg/m2 (HR, 0.61; 95% CI, 0.43-0.86). No significant associations were noted for total fish or fatty fish intake, or LCn-3PUFA from supplements.
Findings were similar when fish intake was evaluated as absolute intake.
In an evaluation of quintile categories of energy-adjusted fish intake and LCn-3PUFA intake, only lean fish was associated with a significantly lower T2D risk. Similar findings were noted when additional covariates, including other food groups and physical activity, were considered.
Along with fish consumption, researchers measured the median intake of methylmercury (MeHg), polychlorinated biphenyls (PCB)-153, and the sum of dioxins and dioxin-line polychlorinated biphenyls (dl-PCBs), which were 0.13 µg/kg body weight/week (IQR, 0.08-0.21), 0.74 ng/kg body weight/day (IQR, 0.49-1.2), and 3.9 pg TEQ-05/kg body weight/week (IQR, 2.8-5.4), respectively.
Lean fish intake correlated with MeHg, while fatty fish intake correlated with PCB-153 and the sum of dioxin and dl-PCBs. In all quintiles, the total sum of dioxins and dl-PCBs exposure—but not MeHG—exceeded the tolerable weekly intake established by the European Food Safety Authority.
“Fatty fish, which contain dioxins and dl-PCBs, did not increase the risk of type 2 diabetes, but the exceedance of the TWI for dioxins and dl-PCBs is a health concern,” the study authors noted.
Study limitations include the use of observational data, potential unmeasured confounders, a lack of generalizability to milder forms of T2D, and a lack of generalizability outside of the study population.
“We observed an association between [the] intake of lean fish, but not of total fish, fatty fish, or LCn-3PUFA supplements, and lower [T2D] risk,” the researchers wrote. “Our results support the current dietary general advice for regular fish consumption, especially among those who are overweight or obese and at a high risk for [T2D].”
“Further research evaluating lean fish intake in diverse study groups and populations, and studies elucidating [the] mechanisms by which lean fish may be protective, are warranted,” the researchers concluded.
Øyen J, Brantsæter AL, Nøstbakken OJ, et al. 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 of Norwegian women. Diabetes Care. Published online August 18, 2021. doi: 10.2337/dc21-0447