Exactly How Important is Obesity in Heart Attack and Stroke Risk?

It is well known that the risk of developing diabetes, high blood pressure, and high cholesterol is increased with overweight or obesity.  However, it's been long debated as to whether obesity itself increases the risk of heart attack and stroke (and if so, how important is this effect), or whether the risk conferred by excess body weight is strictly mediated by these risk factors.

A new study in the Lancet puts some numbers on these answers for us.  The study pooled data from 1.8 million people from almost 100 different studies globally, and they looked at what percentage of heart attack and stroke risk was attributable to blood sugar, blood pressure, cholesterol, vs overweight and obesity themselves.

They found that for every 5 kg/m2 increase in body mass index (you can calculate your own BMI here in the right hand column), the risk of heart disease went up by 27%, and the risk of stroke increased by 18%.  They found that only about half of the excess risk of heart disease with higher BMI was mediated by blood sugar, blood pressure and cholesterol, and about three quarters for the risk of stroke.

In other words, about half of the risk of heart disease, and about a quarter of the risk of stroke, appears to be mediated by excess body weight itself (and/or possibly unknown risk factors), independent of these other risk factors.

The take home messages here, as I see it, is that it is not enough to treat the blood sugar/pressure/cholesterol abnormalities in a person who carries excess body weight, nor is it enough to target weight management alone - all too often, we see these risk factors go untreated for years as individuals continue to try the lifestyle approach, unfortunately most often without success. These risk factors need to be proactively treated, in addition to a sound approach to permanent lifestyle changes that will facilitate weight management and improvement in these risk factors.

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