The effect of omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation on glycaemic control in T1D remains unclear^{(Reference De Caterina, Madonna and Bertolotto1)}. Additionally, the effects of n-3 PUFA on postprandial glucose control in T1D are unknown. Here, we report the effect of 6-month supplementation with a daily high-dose-bolus of n-3 PUFA on parameters of glycaemic control in people with T1D.

For this double-blind, randomized, placebo-controlled trial, individuals with T1D (n = 18; males: 14; 35 ± 15 years; BMI: 26.6 ± 5.2 kg/m²; glycated haemoglobin (HbA_1c): 59 ± 13 mmol/mol^-1 [7.5 ± 3.3%]), were randomly allocated in a 1:1 ratio to receive either 3.3 g/day of encapsulated n-3 PUFA or placebo (PLA) consisting of an encapsulated dose of 3.0 g/day corn oil for 6-months. Venous blood samples were obtained at baseline, and 6-months, to determine HbA_1c, fasting plasma glucose (FPG), and postprandial glucose responses (PPGR) to a standardised mixed-meal tolerance test assessed by area under the curve over a 4-hour period. Fatty acids were measured in erythrocyte membranes by gas chromatography with n-3 PUFA index (O3I) calculated as eicosapentaenoic acid plus docosahexaenoic acid. Paired-samples t tests were used to compare intragroup mean differences with statistical significance set at p ≤ 0.05. Data are presented as mean ± SD.

In the n-3 PUFA group, baseline O3I increased from 4.97 ± 0.98% to 8.24 ± 1.52% after 6-months (p < 0.001). O3I in PLA did not change (baseline: 4.31 ± 1.22% vs. 6-months: 4.58 ± 1.59%, p = 0.256). In the n-3 PUFA group, the mean difference between baseline and 6-months for HbA_1c (-3.89 ± 6.05 mmol/mol^-1; p = 0.090), FPG (-1.04 ± 2.82 mmol/L^-1; p = 0.301), and PPGR (-607.03 ± 2014.63 mmol/L^-1/min^-1; p = 0.392) did not significantly differ. Similar findings were observed in the PLA group; HbA_1c (p = 0.208), FPG (p = 0.624), and PPGR (p = 0.966). Overall, no safety issues arose during administration of n-3 PUFA or PLA.

Supplementation with a daily high-dose-bolus of n-3 PUFA for 6-months did not modulate HbA_1c, FPG, or PPGR to a mixed-meal tolerance test in people with T1D. These findings do not support the use of n-3 PUFA supplementation as an adjunct therapy in the management of T1D.