Serum zinc levels in diabetic patients and effect of zinc supplementation on glycemic control of type 2 diabetics

OBJECTIVE: The present study is an attempt to assess serum zinc level in a sample of diabetic patients (both type 1 and type 2 diabetics) in comparison with those of apparently healthy controls, and to ascertain the relationship between the levels of serum zinc with some epidemiological variables. Furthermore, a trial of zinc supplementation for 3 months conducted to assess the effect of zinc supplementation on glycemic control of the studied type 2 diabetic patients, and the factors that affect the response to this supplementation.

METHODS: Collection of data was carried out during the period between November 2002 to February 2003 at the Diabetic Center of Merjan Teaching Hospital in Babil Governorate, Iraq. In the first part of the study (a case-control study), the diabetic group included 133 diabetic patients (type 1 and 2) who were chosen from patients attending the Diabetic Center during the period of the study. The control group included 133 apparently healthy subjects who were selected from the workers of the same hospital. Selection of cases and controls was carried out by using systematic random sampling procedure. In the second part of the study (single blind were intervention study), type 2 diabetic patients (101 patients) divided into 2 groups; the first group included 50 patients supplemented with oral zinc sulfate (30 mg of elemental zinc/cap/day) for 3 months and second group included 51 patients given placebo and designed as control group.

RESULTS: The first part of the study shows that the mean value for serum zinc level was significantly lower in diabetic patients than healthy controls (64.2 ± 12.6 ug/dl for type 1 diabetics, and 68.9 ± 11.9 ug/dl for type 2 diabetics versus 83.4 ± 12.5 ug/dl for healthy controls). Using simple linear regression, significant positive correlation was found between serum zinc level and years of education and significant negative correlation was found between serum zinc level and baseline HbA1c% value, in the diabetic group. While significant positive correlation found between serum zinc level and estimated zinc intake in the control group. Using multiple regression analysis, serum zinc level showed significant positive correlation with gender (being a male compared with female), and estimated zinc intake and significant negative correlation with diabetes state (diabetic compared with non-diabetic), residence (urban compared with rural residents), and plant protein intake. The second part of the study shows that the mean value for HbA1c% concentration of the supplemented group decreased significantly at the end of the 3 months of follow up, while no significant changes were found in the mean value for HbA1c% of the control group. The present study showed that the change in HbA1c% after supplementation had significant negative correlation with baseline HbA1c% value.

CONCLUSION: Diabetic patients have significantly lower mean serum zinc levels compared with healthy controls. Zinc supplementation for type-2 diabetics has beneficial effects in elevating their serum zinc level, and in improving their glycemic control that is shown by decreasing their HbA1c% concentration.