Effects of zinc and α-linolenic acid supplementation on glycemia and lipidemia in women with type 2 diabetes mellitus: a randomized, double-blind, placebo-controlled trial

Background: Nutritional supplements are used commonly by people with type 2 diabetes mellitus (T2DM). We aimed to investigate the effects of zinc and α-linolenic acid (ALA) supplementation on markers of glycemia (glucose, HbA1c, insulin) and lipid levels (total cholesterol (TC), high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, and triglycerides) in T2DM. Methods: A randomized, double-blind, placebo-controlled, trial in postmenopausal women with T2DM. Participants received zinc (40 mg/d) and/or ALA (2g/d flaxseed oil) for 12 weeks. Results: In participants supplemented with zinc, the differences between initial (week 0) and final (week 12) HDL cholesterol levels and the TC:HDL ratio were marginally significant (-0.1 ± 0.04 mmol/L and +0.1 ± 0.1, respectively; P=0.04). An inverse relationship (r=-0.59, P=0.04) between the changes in HDL cholesterol and HbA1c after 12 weeks was observed in the group supplemented with zinc. No significant effects of ALA treatment on glycemia or lipidemia were observed. Conclusions: In contrast to many studies, the participants in the present trial represent a population with medically controlled T2DM and plasma zinc concentrations within the normal range. The effects of zinc on the lipid profile are similar to those reported in healthy populations, suggesting that medications commonly prescribed in the first-line treatment of T2DM may mask metabolic responses to zinc.