Influence of climate on the incidence of thiazide-induced hyponatraemia

The role of hot temperature has been implicated in thiazide-induced hyponatraemia; however, it has never been studied in a systematic manner. The aim of this retrospective study is to correlate the incidence of thiazide-induced hyponatraemia and climate factors in a university teaching hospital from June 1996 to February 2002. We evaluated a representative sample of 201 subjects with thiazide-induced hyponatraemia. Overall, 2.9 +/- 2.2 (range 0-10, median 3) cases of thiazide-induced hyponatraemia were encountered each month during the study period. There was no seasonal variation in the rate of thiazide-induced hyponatraemia (overall chi(2) test, p = 7.0). Thiazide-induced hyponatraemia was not more frequently reported in summer. There was no discernible correlation between the monthly number of cases and average air temperature (r = -0.056, p = 0.65) and relative humidity (r = 0.103, p = 0.40). On the other hand, patients who presented with thiazide-induced hyponatraemia in July and August had significantly higher serum sodium concentration, 118 +/- 7 mmol/l vs. 114 +/- 8 mmol/l in other calendar months (p = 0.016). Temperature showed a statistically significant positive correlation with the level of serum sodium (r = 0.20, p = 0.004). These data demonstrate that there are no seasonal variations in thiazide-induced hyponatraemia disorders, at least in countries with subtropical climate. The question arises whether hypotonic sweat loss mitigates the risk of excessive water drinking in hot summer.