Serum n-6 polyunsaturated fatty acids, Δ5-and Δ6-desaturase activities, and risk of incident type 2 diabetes in men: the Kuopio Ischaemic Heart Disease Risk Factor Study

Background: The role of n-6 (omega-6) polyunsaturated fatty acids (PUFAs) in type 2 diabetes (T2D) is inconclusive. In addition, little is known about how factors involved in PUFA metabolism, such as zinc, may affect the associations. Objectives: We investigated the associations of serum n-6 PUFAs and activities of enzymes involved in PUFA metabolism, Delta 5 desaturase (D5D) and Delta 6 desaturase (D6D), with T2D risk to determine whether serum zinc concentrations could modify these associations. Design: The study included 2189 men from the prospective Kuopio Ischaemic Heart Disease Risk Factor Study, aged 42-60 y and free of T2D at baseline in 1984-1989. T2D was assessed by self-administered questionnaires, by fasting and 2-h oral-glucose-tolerance test blood glucose measurement at re-examination rounds 4, 11, and 20 y after baseline, and by record linkage to the hospital discharge registry and the reimbursement register on diabetes medication expenses. Multivariate-adjusted Cox proportional hazards regression models were used to analyze associations. Results: During the average follow-up of 19.3 y; 417 men developed T2D. Those with higher estimated D5D activity (extreme-quartile HR: 0.55; 95% CI: 0.41, 0.74; P-trend < 0.001) and higher concentrations of total n-6 PUFAs (HR: 0.54; 95% CI: 0.41, 0.73; P-trend < 0.001), linoleic acid (LA; BR: 0.52; 95% CI: 0.39, 0.70; P-trend < 0.001), and arachidonic acid (AA; BR: 0.62; 95% CI: 0.46, 0.85; P-trend = 0.007) had a lower risk and those with higher concentrations of gamma-linolenic acid (GLA; BR: 1.28; 95% CI: 0.98, 1.68; P = 0.021) and dihomo-gamma-linolenic acid (DGLA; BR: 1.38; 95% CI: 1.04, 1.84; P-trend = 0.005) and higher D6D activity had a higher (HR: 1.50; 95% CI: 1.14, 1.97; P-trend < 0.001) multivariate-adjusted risk of T2D. Zinc mainly modified the association with GLA on T2D risk, with a higher risk observed among those with serum zinc concentrations above the median (P-interaction = 0.04). Conclusions: Higher serum total n-6 PUFA, LA, and AA concentrations and estimated D5D activity were associated with a lower risk of incident T2D, and higher GLA and DGLA concentrations and estimated D6D activity were associated with a higher risk. In addition, a higher serum zinc concentration modified the association of GLA on the risk of T2D.