Effects of diurnal variations in temperature on non-accidental mortality among the elderly population of Montreal,Québec, 1984–2007

The association between ambient temperature and mortality has been studied extensively. Recent data suggest an independent role of diurnal temperature variations in increasing daily mortality. Elderly adults—a growing subgroup of the population in developed countries—may be more susceptible to the effects of temperature variations. The aim of this study was to determine whether variations in diurnal temperature were associated with daily non-accidental mortality among residents of Montreal, Québec, who were 65 years of age and over during the period between 1984 and 2007. We used distributed lag non-linear Poisson models constrained over a 30-day lag period, adjusted for temporal trends, mean daily temperature, and mean daily concentrations of nitrogen dioxide and ozone to estimate changes in daily mortality with diurnal temperature. We found, over the 30 day lag period, a cumulative increase in daily mortality of 5.12 % 95 % confidence interval (CI): 0.02–10.49 %] for a change from 5.9 °C to 11.1 °C (25th to 75th percentiles) in diurnal temperature, and a 11.27 % (95%CI: 2.08–21.29 %) increase in mortality associated with an increase of diurnal temperature from 11.1 to 17.5 °C (75th to 99th percentiles). The results were relatively robust to adjustment for daily mean temperature. We found that, in Montreal, diurnal variations in temperature are associated with a small increase in non-accidental mortality among the elderly population. More studies are needed in different geographical locations to confirm this effect.