Zinc supplementation for the prevention of type 2 diabetes mellitus

The chronic hyperglycaemia of diabetes is associated with long-term damage, dysfunction, and failure of various organs, especially the eyes, kidneys, nerves, heart, and blood vessels. The risk of developing type 2 diabetes increases with age, obesity, and lack of physical activity. Insulin resistance is a fundamental aspect of the aetiology of type 2 diabetes. Insulin resistance has been shown to be associated with atherosclerosis, hypertriglyceridaemia, glucose intolerance, dyslipidaemia, hyperuricaemia, hypertension and polycystic ovary syndrome. The mineral zinc plays a key role in the synthesis and action of insulin, both physiologically and in diabetes mellitus. Zinc seems to stimulate insulin action and insulin receptor tyrosine kinase activity. To assess the effects of the zinc supplementation in the prevention of type 2 diabetes mellitus. Studies were obtained from computerised searches of MEDLINE, EMBASE, LILACS and The Cochrane Library. Studies were included if they had a randomised or quasi-randomised design and if they investigated zinc supplementation in adults living in the community, 18 years or older with insulin resistance (compared to placebo or no intervention). Two authors selected relevant trials, assessed methodological quality and extracted data. Only one study met the inclusion criteria of this review. There were 56 normal glucose tolerant obese women (aged 25 to 45 years, body mass index 36.2 +/- 2.3 kg/m(2)). Follow-up was four weeks. The outcomes measured were decrease of insulin resistance, anthropometric and diet parameters, leptin and insulin concentration, zinc concentration in the plasma and urine, lipid metabolism and fasting plasma glucose. There were no statistically significant differences favouring participants receiving zinc supplementation compared to placebo concerning any outcome measured by the study. There is currently no evidence to suggest the use of zinc supplementation in the prevention of type 2 diabetes mellitus. Future trials will have to standardise outcomes measures such as incidence of type 2 diabetes mellitus, decrease of the insulin resistance, quality of life, diabetic complications, all-cause mortality and costs.