Two hundred eighty-four female adults (aged 40-70 years) were longitudinally studied to investigate the relationship between dietary supplemental
vitamin A and serum
biochemical markers of
vitamin A toxicity. Serum
retinol,
retinyl esters, and
retinol-binding protein (RBP),
alkaline phosphatase and
aspartate aminotransferase activities and
bile acids were measured at baseline, 1 and 2 years. Fasting serum
retinol and
retinyl ester concentrations were determined by high-performance liquid chromatography, and dietary and supplemental intake of
vitamin A were assessed by 3-day food records. There was no difference in dietary
vitamin A intake between supplement users and nonusers. In supplemental users, the mean +/- SEM supplemental
vitamin A intake was 952 +/- 81 IU/day (range 250-5000
retinol equivalents/day). Serum
retinol,
retinyl esters, and RBP concentrations were not different between the two groups during the 2-year period. For each group, serum
retinyl esters significantly increased over time (p < 0.03), but the magnitude of the increase was not different between the groups. Serum levels of
retinol,
retinyl esters, and RBP were not correlated with
vitamin A intake or age in either group. Biochemical measures of liver damage (serum
alkaline phosphatase and
aspartate aminotransferase activities and serum
bile acids) were not related to serum
retinol,
retinyl esters or RBP concentrations, nor were they different between nonusers and users of supplemental
vitamin A. This study provides evidence that long-term supplemental
vitamin A in doses commonly found in multivitamin supplements does not present a risk for
hypervitaminosis A.