A pooled analysis of 97 prospective studies from around the world found that the increased risk of heart disease or stroke in overweight and obese people is partly because their weight increases their chances of having high blood pressure, high cholesterol and high blood glucose.
The study, by a worldwide research consortium led by a team from Harvard School of Public Health (HSPH), Imperial College London, and the University of Sydney, covered a total of 1.8 million participants. The findings are published in The Lancet
Worldwide, obesity has nearly doubled since 1980, according to a previous study by the research team, and more than 1.4 billion adults aged 20 and older are overweight or obese. Being overweight increases one's risk of heart disease and stroke the leading causes of death worldwide diabetes, and several types of cancer. The researchers had also previously estimated that 3.4 million annual deaths are due to overweight and obesity.
There has been debate over whether excess weight causes heart disease and stroke through effects on other risk factors, particularly blood pressure, cholesterol, and glucose, and whether treatments that address these factors can offset the risks of being overweight.
The study found that high blood pressure, serum cholesterol, and blood glucose explain up to half of the increased risk of heart disease and three quarters of the increased risk of stroke among overweight or obese people. High blood pressure poses the biggest risk of the three metabolic factors examined, accounting for 31 per cent of the increased risk of heart disease and 65 per cent of the increased risk of stroke.
"Our results show that the harmful effects of being overweight or obese on heart disease and stroke partly occur by increasing blood pressure, serum cholesterol and blood glucose. Therefore, if we control these risk factors, for example through better diagnosis and treatment of hypertension, we can prevent some of the harmful effects of being overweight or obese," said senior author Goodarz Danaei, HSPH assistant professor of global health.
Co-author Professor Majid Ezzati, from the School of Public Health at Imperial College London, said: "Controlling hypertension, cholesterol, and diabetes through medication is useful, but not enough to offset the harms of overweight and obesity. So we need to need to find creative approaches that can curb and reverse the global obesity epidemic."
Professor Stephen Hill, Chair of the Medical Research Council's Molecular and Cellular Medicine Board, which part-funded the work, said: "Large, long-term population studies like this one are a very powerful tool, allowing researchers to disentangle individual factors and understand how they each contribute to our risk of disease. It's interesting that, even when blood pressure, blood sugar and cholesterol are brought under control, obese individuals are still at a higher risk of heart attack and stroke. This suggests that other factors might be at play, which is likely to be of interest for future research into the consequences of obesity."