Abstract
Although the metabolism of vitamin A in diabetes has been investigated by many early and recent workers the results are conflicting. Also, it has been observed that zinc plays an important role in vitamin A metabolism. This thesis describes a study of vitamin A in two groups of diabetic patients with an additional study on experimental animals. Study 1 deals with a case-control study that involve 110 patients with Type 2 diabetes mellitus (DM) matched in age and sex with 143 healthy controls. The study is designed to evaluate status of vitamin A and related factors in patients with Type 2 DM. After correction for the cholesterol and triglyceride levels, concentrations of serum retinol, a-carotene, a-tocopherol, zinc, copper and cholesterol were similar in diabetic patients Type 2 and control subjects. However, the mean serum B-carotene was significantly lower in diabetic patients than in control individuals (P < 0. 003). When compared with controls, patients with Type 2 diabetes mellitus had significantly higher concentration of serum and urine retinol-binding protein (RBP) (both P < 0. 0001). Urine concentrations of zinc and serum concentrations of triglycerides were significantly higher in patients with Type 2 DM than those in controls (P < 0. 0002, P < 0. 0001, respectively). Urine concentrations of creatinine were significantly lower in patients with Type 2 DM than those in controls (P < 0. 0001). Furthermore, diabetic patients with nephropathy had significantly higher excretion of RBP and significantly lower serum concentrations of zinc when compared to other diabetic or to controls. There was a significant negative correlation between FBG and B-carotene (r = -0. 18, P < 0. 05) in the total group. Possible reasons for these differences are discussed. Food frequency consumption and 24 h dietary recall for diabetic patients and controls were evaluated. Study 2 deals with 175 diabetic patients with Type 1, Type 2, renal impairment, and chronic renal failure(CRF). Non-diabetic patient with CRF were matched in age and sex with the diabetic patients with CRF. This study attempts to examine the association of Haemoglobin A1c with vitamin A and related factors and investigate further retinol, a-carotene, B-carotene, a-tocopherol and RBP in those patients. Patients with Type 1 DM had significantly lower plasma concentrations of retinol, a-tocopherol and RBP when compared with patients with Type 2 DM, diabetic patients with renal impairment, diabetic and non-diabetic patients with CRF. Diabetic patients with CRF or with renal impairment had significantly higher plasma concentrations of retinol and B-carotene when compared to other groups (Type 1 and Type 2). In the third study, the effect of supplementation with B-carotene on fasting blood glucose (FBG) and lipid levels was studied in streptozotocin-diabetic Wistar male rats. . The incidence of diabetes in the late supplemented diabetic group (which had received five weeks’ supplementation prior to STZ) was lower (59%, 10 of 17) than in the early supplemented diabetic group (76%, 19 of 25). However, the difference was not statistically significant (p = 0. 135). Mean FBG, triglycerides, LDL-C and HDL-C were lower in both supplemented diabetic groups than controls. The results suggest that supplementation with the anti-oxidant pro-vitamin B-carotene may confer resistance to the development of diabetes, resulting in improvement in both glucose and lipid levels.