Fresh feces from 104 infants and children (aged 3 days to 16 years) were homogenized and incubated with labeled cholic or chenodeoxycholic acid. After 2 and/or 24 hours' incubation, the percentage of converted (mostly 7α-dehydroxylated) primary bile acids was measured, and the degree of conversion was correlated with serum cholesterol levels. It was found that stool homogenates of patients with low levels of serum cholesterol (< 160 mg/100 ml) converted labeled primary bile acids poorly or not at all, whereas in patients with higher serum cholesterol levels (> l60 mg/100 ml) the conversion process was markedly increased. Thus, highly significant correlations were found between serum cholesterol levels and the capability of the fecal bacterial flora to convert both primary bile acids "in vitro."
The possibility is proposed that in man the relatively rapid progressive increase of serum cholesterol level following birth may be related to the colonization of the intestinal tract by 7α-dehydroxylating and/or bile acid degrading bacteria. It is suggested that the prevalence of these bacteria is subject to environmental effects, and it may be one of the important factors regulating cholesterol levels in man.