Cold and winter mortality from cardiovascular diseases in Guangzhou, China

Abstract

Background/Aims: Many studies have linked elevated ambient temperature and heat waves to cardiovascular deaths. However, despite of the enormity of winter excess mortality from cardiovascular diseases (CVD), the effects of cold exposure are not well documented. We assessed the cold-related mortality from CVD in Guangzhou, a subtropical city in southern China.

Methods: We obtained meteorological data from National Climatic Data Center and mortality data from Guangzhou Department of Health. The study included 43,401 cardiovascular deaths, accounting for 37% of all-cause deaths during the period of 2003 to 2007. Cold exposure was measured using the average ambient temperature over the proceeding 0–4 days. A time-stratified case-crossover design with conditional logistic regression modeling was conducted to examine the association between daily temperature and mortality from CVD during winter periods (December to March), after adjusting for day of the week and daily mean humidity. We considered the potential effect modification by individual characteristics, including age, sex, and education level.

Results: The mortality rate in winter was 15.13% higher than the average in the whole year. The winter excess mortality from CVD was up to 22.14%. We found that 1°C fall of daily mean temperature in winter was associated with a 2.44% (95% confidence interval [CI]: 1.88%–3.01%) increase in mortality from CVD. Very similar associations were found with mortality from stroke (2.26%, 95% CI: 1.30%–3.24%) and coronary heart diseases (2.53%, 95% CI: 1.52%–3.55%). The effects were greater in males than in females. The effects of cold exposure tended to increase with individual's education level. There was little evidence that the cold effects we found reduced over time.

Conclusion: Mortality from CVD presented a clear seasonality with dramatic rises in winter. Our results indicate that cold exposure is a main environmental cause of high winter mortality even in subtropics.