Scientists found that poverty and poor education are linked to ill health and early death, and should be considered risk factors for these outcomes.
The research by Imperial College London showed that low socioeconomic status (SES) had almost the same impact on health than smoking or a sedentary lifestyle, and was associated with reduced life expectancy of 2.1 years, similar to being inactive (2.4 years).
SES is a measure of an individual or family's economic and social position in relation to others, based on income, education and occupation.
Health policies often don't consider risk factors such as poverty and poor education when predicting health outcomes.
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Professor Paolo Vineis from Imperial College London and colleagues studied 1.7 million people in the UK, France, Switzerland, Portugal, Italy, US and Australia.
They used people's job titles to estimate their SES and looked at whether they died early (before age 85.)
They then compared SES against the main risk factors (tobacco use, unhealthy diet, physical inactivity and harmful use of alcohol) as defined by the World Health Organisation in its Global Action Plan for the Prevention and Control of Non-Communicable Diseases.
The researchers found that, compared to their wealthier counterparts, people with low SES were 46 per cent more likely to die early.
They calculated the number of years of life lost for various factors, and compared this to SES. They found the greatest number of years lost were for smoking and diabetes (life expectancy reduced by 4.8 and 3.9 years, respectively).
Comparatively, high blood pressure, obesity and high alcohol consumption were associated with fewer life years lost (1.6, 0.7 and 0.5 years, respectively) than low SES.
"Factors linked to socioeconomic status, such as poverty and poor education, are hugely important in predicting health outcomes," said Vineis.
"Our study shows that low SES is just as important as tobacco use, unhealthy diet, physical inactivity and harmful use of alcohol. As a result, we argue that low SES should be included in health policies alongside the other factors," Vineis added.