Seasonal variation in the incidence of end-stage renal disease

The effect of ambient temperature (AMT) on the incidence of end-stage renal disease (ESRD) was examined in Okinawa, Japan, where there is a distinct seasonal variation in monthly AMT but constant intradiurnal temperature change throughout a year. Arbitral continuous and cyclic functions were examined using Fourier analysis and calculation of the cross-correlation coefficient. The calendar month of the start of chronic dialysis was regarded as the time of onset of ESRD. A total of 1,982 patients, 824 females and 1,158 males, was registered with ESRD between 1971 and 1990. The normalized monthly number of new ESRD patients, divided by days of each month, was smallest in August, n = 4.06, and largest in January, n = 6.45, and this pattern was well reproduced by the Fourier synthesized value. The cross-correlation coefficient showed that monthly mean AMT and the normalized number of ESRD patients correlated best with 6 months lag time. Taken together, our results showed that there was strong correlation between the normalized number of ESRD patients and AMT. Uremic symptoms leading to initiate dialysis, such as congestive heart failure, may be aggravated in lower AMT. We speculated a role of an inverse relation between AMT and the sympathetic nerve function. The public health implications of these findings warrant their further investigation.