Objective: A case-control study was conducted to evaluate the effects of diabetes mellitus on serum levels of vitamin A, alpha-carotene, beta-carotene, alpha-tocopherol, serum and urine RBP.
Subjects: One hundred and seven patients with Type 2 diabetes mellitus (28-74 y) were recruited from those attending a primary health care clinic in King Khalid University Hospital in Riyadh City (Saudi Arabia). They were matched for age and sex with 143 healthy individuals.
Methods: Fasting blood samples and 10h urine collections were obtained from all subjects. Levels of vitamins and carotenoids in serum measured by high performance liquid chromatography (HPLC), and of retinol binding protein (RBP) in serum and urine by an enzyme-linked immunosorbent assay (ELISA).
Results: The mean serum concentrations of retinol, alpha-carotene, and alpha-tocopherol were similar in both groups after correction of lipid soluble vitamins for serum lipids levels. However, serum beta-carotene concentration was significantly higher in control subjects than diabetics (P = 0.002). Serum and urine RBP concentrations were significantly higher in diabetics than in controls (P = 0.0001). In normal subjects (but not diabetics) serum concentrations of retinol and RBP were higher in men than in women (P = 0.02, P = 0.0001 respectively). In both normal and diabetic subjects, serum levels of alpha-tocopherol (P = 0.007) and urine RBP (P = 0.005), were higher in men than women. Urinary excretion of RBP was significantly higher in diabetic patients with renal impairment than other diabetics or controls (P = 0.0001). There was a negative correlation between fasting blood glucose (FBG) concentration and serum beta-carotene (P = 0.008) in the total combined group and a positive correlation between FBG and urinary RBP/creatinine (P = 0.009) in diabetic patients.
Conclusion: Serum beta-carotene concentration was significantly lower in diabetic patients than controls. Serum retinol concentration in patients with diabetes was normal, yet serum and urine RBP concentrations were significantly higher in diabetics than in controls.