This is the first time that body mass index (BMI) – an internationally recognised index of weight for height – has been shown likely to have a causal link to detailed measures of cardiovascular health in a population of young, healthy people. Using data and participants from Bristol’s Children of the 90s study, this research in healthy participants will help understanding of the importance of body composition in later life outcomes and disease.

Researchers first looked the relationship between BMI and routinely collected cardiovascular measures, such as blood pressure and heart rate, in more than 3000 17-year olds. Then they worked with more than 400 21-year old participants (again from the Children of the 90s study), to undertake detailed cardiovascular scans in those who had differences in their BMI that could be anticipated by genetic data.

Using a variety of methods, researchers were able to conclude that variation in BMI is likely to be causally linked to differences in cardiovascular health in young age. Until now, most studies have looked at the association between BMI and cardiovascular health in adults and have used traditional approaches that suffer from limitations, which authors attempted to overcome with their study design and with access to the unique opportunity in Children of the 90s.

Research Associate in the Medical Research Council Integrative Epidemiology Unit at the University of Bristol Dr Kaitlin Wade said: "Our results support the idea that having a healthy BMI level from a young age is likely to prevent later heart disease."

"Modern genetics, the study of an organism’s DNA, allows us to study the causes of disease more quickly and cheaply, and the availability of genetic data in the Children of the 90s study means we can overcome previous limitations of traditional studies. There are clear messages for heart health in young people from our findings and we hope that they lead to increased efforts to tackle elevated BMI throughout life."

The researchers found that even healthy participants with a higher BMI on average had:

• Higher systolic (top number) and diastolic (bottom number) blood pressure;
• An enlarged left ventricle, the heart’s main pumping chamber; but
• Did not cause thickening of the vessel walls in the carotid artery or increase heart rate

The British Heart Foundation partially funded the research alongside the Medical Research Council, the University of Bristol and The Wellcome Trust.

Chris Allen, Senior Cardiac Nurse at the British Heart Foundation, said: "Being overweight or obese causes increased blood pressure and damaging changes to the structure of the heart, which increases the risk of heart problems. This research makes it clear that it is never too early to start thinking about your heart health, as being an unhealthy weight can damage the structure of your heart, even in early adulthood.

"Maintaining a healthy weight at any stage of life, gives you the best chance of a healthy heart and circulation in later life."

The next steps are for researchers to look at why measures of BMI, or body composition, are related in an apparently causal way to cardiovascular health. The dissection of pathways from BMI to disease may help to establish where interventions may be most effective and the mechanisms of disease.

Paper:

‘Assessing the causal role of body mass index on cardiovascular health in young adults: Mendelian randomization and recall-by-genotype analyses’ by Kaitlin H Wade et al in Circulation