INTERACTIONS OF VITAMIN-A AND VITAMIN-E AND RETINOL-BINDING PROTEIN IN HEALTHY SWEDISH CHILDREN EVIDENCE OF THRESHOLDS OF ESSENTIALITY AND TOXICITY

The serum levels of vitamins A and E and retinol-binding protein (RBP) were determined and their relationships investigated in 144 healthy Swedish children between the ages of 1 month and 16 years. The median level for vitamin A was 540 mug l-1 (range 181-1720 mug l-1); for vitamin E 6.8 mg l-1 (range 1.0-14.0 mg l-1) and for RBP 0.030 g l-1 (0.018-0.045 g l-1). Retinol-binding protein levels rose steeply in relation to vitamin A levels of up to approximately 800 mug 1-1. However, RBP levels remained constant when vitamin A levels were between 800 and 1600 mug l-1 but displayed a further steep rise for vitamin A levels above this range. Fourteen individuals had levels that did not follow this pattern but fell rather neatly below the correlation line. These individuals were also found to have significantly higher mean levels of acute phase reactants than the rest of the study group, suggesting the possibility of subclinical infection or inflammation in these subjects. Vitamins A and E showed an inverse curvilinear relationship. This is the first report of an interaction between vitamins A and E and RBP in healthy Swedish children. The study demonstrates that a linear one-to-one relationship between RBP and vitamin A may not be of regular occurrence as previously assumed. The pattern described suggests the existence of thresholds of essentiality and toxicity in the interaction between the two vitamins and RBP. The study also shows the importance of checking for possible subclinical infection and inflammation even in apparently healthy and well nourished children.