Effects of Antioxidant Micronutrients against CVD Risk in Type 2 Diabetes Mellitus: A Systematic Review

Abstract

Diabetes mellitus is associated with hyperglycemia, which promotes oxidative stress through production of free radicals which may lead to diabetic complications such as cardiovascular diseases. However,it is proposed that dietary intakes of antioxidant micronutrients may help reduce oxidative stress in diabetes mellitus. The objective was to evaluate the protective effects of antioxidant micronutrients against CVD risk among type 2 diabetics. Method: A systematic literature review including detailed search strategy was developed to search PubMed, PMC, PLOSONE, Google scholar and cochrane. Research articles were retrieved, screened and relevant articles were extracted. The exposure for review were zinc, vitamin E, and selenium, whereas measured outcomes were effects of antioxidant micronutrients on type 2 diabetes: reduced FBG and HbA1c, reduced lipidemia, improved antioxidant status, reduced oxidative stress. Results: Among six cross-sectional studies; five studies indicated serum zinc were significantly reduced in type 2 diabetics than controls, whereas one study showed a higher serum selenium in type 2 diabetics than controls. Among five case-control studies used, two studies found serum zinc was lowered among type 2 diabetics than controls. Another study found serum vitamin E was reduced in type 2 diabetics than controls (p<0.05). The other studies showed supplementation of vitamin C, E improved significantly in levels of fasting blood glucose and glycated hemoglobin (p<0.05, p<0.001 respectively). However, a case control study between type 2 diabetics with glycated haemoglobin <7% and ≥ 7% showed no difference in serum zinc levels (p=0.168). Out of five randomized controlled trials, two studies showed significant difference in fasting blood glucose, total antioxidant capacity, malondialdehyde in type 2 diabetics who received supplemented enriched tocotrienol canola oil at the end of study. However, type 2 diabetics supplemented with omega-3 plus vitamin E, and zinc plus vitamin C showed no significant differences in cardiovascular risk markers compared to controls. Also, two studies which either supplemented type 2 diabetics with fermented diet containing supplemented chromium and zinc found no significant differences in glycated hemoglobin compared to placebo groups. Conclusion: Antioxidant micronutrients could significantly reduce risk of cardiovascular diseases in type 2 diabetes and hence require further studies to ascertain its effects.