“Pilot clinical studies suggest that this effect may be mediated, in whole or in part, by an increase in serum 25-hydroxyvitamin D. We propose that, in concentrations achievable with good diets, boron suppresses the activity of the microsomal enzyme 24-hydroxylase, chiefly responsible for catabolism of this steroid.”
“This suggests the more general hypothesis that nutritional boron can inhibit a range of microsomal enzymes which insert hydroxyl groups vicinal to existing hydroxyls in steroids -- including the enzymes which catabolize estradiol and 25-hydroxyvitamin D.”