Smoking and cardiovascular disease may explain sex-related differences in mortality

1. In a cohort study spanning 28 high-income countries, men had a 60% higher mortality risk than women.

2. This mortality risk was reduced by 22% when adjusting for both smoking and cardiovascular disease, suggesting that these factors may be responsible for the disparity in life expectancy between sexes.

Evidence Rating Level: 2 (Good)

Study rundown: Life expectancy for men has consistently been found to be lower than women, although the male-to-female mortality ratio has decreased over the last 30 years. It has been thought that this gap in mortality is due to biological differences, which confer greater resilience in women. However, gender as a social construct may tie into societal, cultural, and economic factors that influence mortality, such as one’s occupation, or one’s health lifestyle factors. Since the construct of gender can vary across cultures, this retrospective cohort study aimed to investigate potential factors that may account for the difference in men and women’s mortality risk, across 28 high-income countries. The study found that men had a 60% higher mortality risk than women. However, when controlling for most lifestyle, health, social, and socioeconomic factors, no significant reduction in risk was found, except for smoking and cardiovascular. When combined, the two factors attenuated the risk by 22%, suggesting that these are major factors accounting for the disparity in life expectancy between men and women. Overall, this study reiterates the greater mortality risk in men across numerous countries, with smoking and cardiovascular disease being contributors to this disparity.

Click to read this article in CMAJ

Relevant Reading: Differences between Men and Women in Mortality and the Health Dimensions of the Morbidity Process

In-Depth [retrospective cohort]: The study population consisted of 179,044 individuals 50 years and older (55% female), with a median (IQR) age of 63 (55-71). The primary outcome was mortality, and factors that were investigated included socioeconomic (level of education, wealth), health (presence of cardiovascular disease, diabetes, hypertension, depression), lifestyle (smoking, alcohol), and social (living alone, romantic status). For mortality, men had a 60% higher risk (pooled hazard ratio 1.6, 95% CI 1.5-1.7). The HR ranged from 1.07 in Mexico (95% CI 0.81-1.41) to 2.44 in Japan (95% CI 1.54-3.85). Furthermore, the association between sex and mortality was only attenuated upon adjusting for two factors: Smoking (HR 1.47, 95% CI 1.39-1.55) and cardiovascular disease (HR 1.56; 95% CI 1.46-1.66). When stratifying age-adjusted HRs for smoking, the sex and mortality association was reduced in nonsmokers and ex-smokers (HR 1.40, 95% CI 1.32-1.49 and HR 1.43, 95% CI 1.32-1.56) respectively. As well, the association was reduced when adjusting for both smoking and cardiovascular disease (HR 1.44, 95% CI 1.36-1.52), and was reduced in nonsmokers with no cardiovascular disease (HR 1.34, 95% CI 1.25-1.44). When the sex and mortality correlation is attenuated after adjustment for a factor (such as smoking), this can suggest that the prevalence of the factor is different between men and women, in contrast to the factor having different effects on men and women. Countries where men had double the mortality risk also appear to have a large sex difference in smoking prevalence.

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