Previous studies have shown increased bone density and reduced risk of fracture in patients taking thiazide diuretics. In vitro, a direct effect of thiazides on osteoblasts has been reported. However, the long-term effects of low-dose thiazides on mineral metabolism have not been reported in normal subjects. The authors of this study [1] conducted a randomized, double-blinded trial in normal subjects aged 60 to 79 years, using hydrochlorothiazide 12.5 or 25 mg/d or placebo for 3 years. Subjects were encouraged to maintain calcium intake of 1 to 1.5 g/day. Measurements of serum and urine calcium metabolism were done at baseline, 6 months, and yearly. Data were analyzed in 88 men and 177 women who had taken study medication. Adjusted changes in the measurements from baseline to 1 and 3 years were compared among groups.

The calcium intake increased in all groups. Urine calcium per day was significantly lower in thiazide than placebo groups in men at 1 year but not at 3 years; in women the changes were not significantly different. Serum bicarbonate was higher in thiazide compared to placebo groups at 1 and 3 years. No changes were seen in serum calcium, phosphate, parathyroid hormone, sodium, or magnesium.

These results suggest that both increased calcium availability from a hypocalciuric effect and reduction in acid-induced bone buffering could be mechanisms for the beneficial skeletal effects. Nevertheless, long-term treatment with thiazides cannot be considered at present as a treatment for osteoporosis.

1. Ott SM et al. Osteoporos Int. 2008;19:1315-1322.