Intestinal absorption and 25-hydroxylation of vitamin D in patients with primary biliary cirrhosis.

The absorption, metabolism, and excretion of vitamin D3 was studied in eight women with an established diagnosis of primary biliary cirrhosis (PBC), and the results were compared with those obtained from eight healthy women of a similar age. Four patients had hyperbilirubinemia, low serum calcium levels, and a reduced mineral content of the bone, whereas the other four were presymptomatic with respect to bone disease. Vitamin D absorption was studied after oral administration of tritiated vitamin D, and the appearance of serum radioactivity was recorded. After this, the liver 25-hydroxylation of vitamin D was studied by administering an intravenous dose of tritiated vitamin D and then chromatographing serum samples to determine the radioactivity of the 25-OH D fraction. All PBC patients had normal 25-hydroxylation capacity of the vitamin, and there was no difference in the urinary excretion of radioactivity. On the other hand, the intestinal absorption of vitamin D was severely impaired both in the symptomatic and asymptomatic patients. The absorption of the vitamin was negatively correlated to the amount of fecal fat, and the results suggest that low serum levels of 25-OH D in symptomatic PBC seem to be caused by the steatorrhea, whereas hepatic conversion of vitamin D into 25-OH D seems to be well preserved even in patients with hyperbilirubinemia and signs of osteomalacia. The absorption-metabolism test may be a valuable tool in the study of patients with cholestatic liver disease for determining the nature of the vitamin D deficiency and the logical form of substitution therapy.