In particular, the study published in the European Heart Journal, shows that as body mass index (BMI) and fat mass increase, so does the risk of aortic valve stenosis – a condition in which the valve controlling the flow of blood from the heart to the body’s largest blood vessel, the aorta, narrows and fails to open fully.
As part of the study, the team of researchers used a method called Mendelian randomisation to explore this phenomenon further.
Mendelian randomisation is a way of showing whether or not individual risk factors actually cause disease, rather than just being associated with it. It uses genetic variants that are already known to be associated with potential risk factors, such as BMI and body fat, as indirect indicators or “proxies” for these risk factors.
This enables researchers to discover whether the risk factor is the cause of the disease (rather than the other way around), and reduces bias in results because genetic variants are determined at conception and cannot be affected by subsequent external or environmental factors, or by the development of the disease.
The researchers, led by Susanna Larsson, associate professor and senior researcher at the Karolinska Institute, studied 96 genetic variants associated with BMI and body fat mass to estimate their effect on 14 cardiovascular diseases in 367,703 participants of white-British descent in UK Biobank — a UK-based national and international resource containing data on 500,000 people, aged 40-69 years.
“The causal association between BMI and fat mass and various heart and blood vessel diseases, in particular, aortic valve stenosis, was unknown. Using Mendelian randomisation we found that higher BMI and fat mass are associated with an increased risk of aortic valve stenosis and most other cardiovascular diseases, suggesting that excess body fat is a cause of cardiovascular disease,” Larsson explained.
The researchers also found that the risk of cardiovascular diseases increased with the genetic variants predicting increases in fat mass. The greatest increased risk was also for aortic valve stenosis (46 per cent increased risk), followed by ischaemic stroke, transient ischaemic attack, atrial fibrillation, heart failure, peripheral artery disease, deep vein thrombosis, high blood pressure, and coronary artery disease.
The researchers stress that although these genetic variants can predispose people to be more likely to gain excess weight, the most important factors implicated in the development of cardiovascular disease are diet and physical activity.
“Our genes can make us somewhat more predisposed to gain body weight but lifestyle factors, such as overeating and lack of physical activity, are the major determinants of overweight. A healthy diet is the cornerstone of cardiovascular disease prevention, and how much we eat should be limited to the amount of energy required to maintain a healthy body weight, which is a BMI of between 20 to 25 kg/m2. People who are predisposed to a higher BMI may need to work a bit harder to maintain a healthy weight,” Larsson asserted.