The interrelationship of thyroid hormones with vitamin A and zinc nutritional status in patients with chronic hepatic and gastrointestinal disorders.

To define the role of vitamin A, retinol binding protein, and zinc deficiency in producing the thyroid hormone abnormalities found in chronic illness, we studied 62 clinically stable patients with hepatic and gastrointestinal disorders. Serum triiodothyronine (T3) and free T3 index (FT3I) were depressed compared to controls (p less than 0.05) in the patients. Retinol binding protein and prealbumin levels correlated with both T3 and FT3I (p less than 0.01), whereas vitamin A levels did not. Vitamin A therapy in patients with documented vitamin A deficiency produced an increase in T3, thyroxine (T4), FT3I, FT4I, and free T3 by dialysis, with a concomitant increase in retinol binding protein and no alteration in prealbumin concentrations. Zinc-deficient patients had significantly depressed T3 and FT3I (p less than 0.001) and increased prolactin levels (p less than 0.01). Zinc supplementation failed to return any of these parameters to normal. Vitamin A therapy in normals produced a transient decrease in T3 and T4 after 1 wk of therapy, but after a further 2 wk, thyroid function returned to normal. Our data suggest a causal relationship between the pathogenesis of deranged vitamin A-retinol binding protein metabolism and the low T3 syndrome either by interfering with T4 entry into tissues or by directly affecting the enzymatic conversion of T4 to T3.