[Diuretics and osteoporosis]

Thiazide diuretics lower while loop diuretics promote calcium excretion by the kidney. Several studies have found thiazide use to be associated with higher bone mineral density and some have found that thiazides reduce the risk of hip fracture. The mechanisms by which thiazides favour preservation of the bones are uncertain. Thiazide use results in decreased renal calcium excretion and thiazide users have been shown to have lower levels of S-PTH and S-1,25-dihydroxy-vitamin D. The beneficial bone effects may result from a decrease in PTH-stimulated bone resorption and an associated reduction in the bone turn-over rate. Whether loop diuretics increases the bone turn-over by augmenting the urinary calcium excretion is more controversial as only few studies have been carried out on loop diuretics. However, in these studies the use of loop diuretics have been associated with decreased bone mineral density and increased risk of fractures. Future research should determine the minimal dose of thiazide therapy necessary to produce a sustained hypocalciuric effect and in addition the influence of diuretic dose on bone turn-over. Equally important is the need to evaluate potential unwanted effects of loop diuretics. In the mean time, thiazide diuretics may be used safely while some caution is necessary in the long term use of loop diuretics in patients who are prone to osteoporosis.