This article was first published in The Montreal Gazette.
Many studies have shown that low socioeconomic status is tied to cardiovascular disease. To put it simply, if you have more money, you are less likely to have a heart attack.
There are many possible ways to explain this association. It might be that more money means you can afford better medical care. It’s also possible that more money means you have the financial freedom to buy healthier food; sadly, we live in a world where junk food is cheaper than fruit. But another possibility is more intriguing. The link might have more to do with smoking than anything else.
Teasing out whether something is actually bad for you or just a marker for some other harmful thing is not always easy. For example, carrying a lighter in your pocket is a pretty good indication you will get lung cancer later in life. The lighter doesn’t cause lung cancer of course, but people who carry lighters tend to be smokers and smokers do have a higher risk of lung cancer.
This type of situation is referred to as confounding, where a third variable can affect the relationship between another two. As I described recently in another article, confounding made Vitamin D seem much more important than it actually was for our health.
But the relationship between socioeconomic status and heart disease is not immediately attributable to just one thing. One way to figure out what factors are driving that relationship is to use a statistical technique called mediation analysis. In this type of analysis, researchers can look at whether two factors are associated, like whether carrying a lighter will predict who will get lung cancer or if socioeconomic status will predict who will get heart disease. They can then introduce other variables into the analysis to see if any of them can explain away the relationship.
When it comes to lighters, accounting for cigarette smoking explains the lung cancer risk entirely. When it comes to socioeconomic status, surprisingly enough, cigarettes also seem to be responsible.
In a paper published earlier this year in the Journal of the American College of Cardiology, researchers tried to explain exactly why socioeconomic status affects cardiovascular disease. Using a mediation analysis, they found that smoking status and the number of cigarettes smoked per day were the main drivers of the cardiovascular risk. Taken together they explained almost 70 per cent of the association between socioeconomic status and heart disease. Dietary patterns contributed very little, only about 3.5 per cent of the risk.
While smoking rates have been on the decline, the practice is still common. The most recent survey data shows that 15 per cent of the population smokes, with just over 10 per cent of Canadians smoking daily. But smoking rates are not spread evenly in our society. When you look at household income, smoking rates range from 12 per cent for those in the highest income bracket to 22 per cent in the lowest. You see the same trend when looking at education and employment levels.
We know that certain segments of the population are at higher risk for heart disease, and people at the lower end of the socioeconomic spectrum are especially so. What to do about it though is not always straightforward. But, this paper suggests at least one way forward.
Over the years, we have had considerable success with anti-smoking laws and restrictions on tobacco advertising, yet smoking persists and the tobacco industry isn’t going to disappear of its own accord. But there is one thing we can do. It is cheap and will actually save people and the health-care system money in the long term. We can get people to quit smoking.
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