Clinical endocrinology
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Clinical endocrinology · Aug 1995
Randomized Controlled Trial Comparative Study Clinical TrialOestrogen effects on calcitriol levels in post-menopausal women: a comparison of oral versus transdermal administration.
In some studies oral oestrogen therapy in post-menopausal women has been shown to increase both total and free 1,25-dihydroxyvitamin D (calcitriol) levels, suggesting that oestrogen therapy may prevent post-menopausal bone loss, in part, by increasing calcium absorption as a result of raised calcitriol levels. Transdermal oestrogen, however, has not been shown to increase calcitriol levels although it prevents bone loss. These two routes of administration have not previously been directly compared in the same subjects at bioequivalent doses as assessed by FSH and LH suppression. ⋯ These results show that in this study the total calcitriol rose after oral but not transdermal oestrogen due to a rise in vitamin D-binding protein. Free calcitriol was not affected by oral or transdermal oestrogen treatment despite a fall in plasma phosphorus and a rise in PTH, both of which are considered agonists for calcitriol production. We may therefore conclude that neither oral nor transdermal oestrogen replacement routinely stimulates free calcitriol levels. In the studies where a rise in free calcitriol was noted, the degree of suppression of bone resorption by oestrogen may have been greater, thus producing a larger demand for calcium due to filling of a larger bone remodelling space with consequent stimulation of calcitriol levels.