Abstract
BackgroundCardiovascular diseases (CVD) mortality has been shown to follow a seasonal pattern. Several studies suggested several possible determinants of this pattern, including misclassification of causes of deaths. We aimed at assessing seasonality in overall, CVD, cancer and non-CVD/non-cancer mortality using data from 19 countries from different latitudes.Methods and FindingsMonthly mortality data were compiled from 19 countries, amounting to over 54 million deaths. We calculated ratios of the observed to the expected numbers of deaths in the absence of a seasonal pattern. Seasonal variation (peak to nadir difference) for overall and cause-specific (CVD, cancer or non-CVD/non-cancer) mortality was analyzed using the cosinor function model. Mortality from overall, CVD and non-CVD/non-cancer showed a consistent seasonal pattern. In both hemispheres, the number of deaths was higher than expected in winter. In countries close to the Equator the seasonal pattern was considerably lower for mortality from any cause. For CVD mortality, the peak to nadir differences ranged from 0.185 to 0.466 in the Northern Hemisphere, from 0.087 to 0.108 near the Equator, and from 0.219 to 0.409 in the Southern Hemisphere. For cancer mortality, the seasonal variation was nonexistent in most countries.ConclusionsIn countries with seasonal variation, mortality from overall, CVD and non-CVD/non-cancer show a seasonal pattern with mortality being higher in winter than in summer. Conversely, cancer mortality shows no substantial seasonality.
Highlights
Hippocrates already recognized that mortality is higher in cooler than in warmer months [1]
In countries with seasonal variation, mortality from overall, cardiovascular disease (CVD) and non-CVD/non-cancer show a seasonal pattern with mortality being higher in winter than in summer
Distributions of overall, cancer and non-CVD/non-cancer mortality are illustrated in Figure S1, Figure S2 and Figure S3
Summary
Hippocrates already recognized that mortality is higher in cooler than in warmer months [1]. Most studies on the seasonality of mortality by cause of death have focused on a single country [6, 13, 14]. We aimed to establish whether a seasonal pattern in overall and cause-specific (CVD, cancer and non-CVD/non-cancer) mortality exists at the worldwide level. We aimed at assessing seasonality in overall, CVD, cancer and non-CVD/non-cancer mortality using data from 19 countries from different latitudes. Seasonal variation (peak to nadir difference) for overall and cause-specific (CVD, cancer or non-CVD/non-cancer) mortality was analyzed using the cosinor function model. Mortality from overall, CVD and non-CVD/non-cancer showed a consistent seasonal pattern. In both hemispheres, the number of deaths was higher than expected in winter. The seasonal variation was nonexistent in most countries
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