Waist to height ratio a better outcome indicator than BMI in patients with heart failure
New research has debunked the idea that there is an “obesity paradox”, whereby patients with heart failure who are overweight or obese are thought to be less likely to end up in hospital or die than people of normal weight.
The new study – published in the European Heart Journal and led by the University of Glasgow – shows that if doctors measure the waist to height ratio of their patients, rather than looking at their body mass index (BMI), the supposed survival advantage for people with a BMI of 25kg/m2 or more disappears.
The “obesity paradox” relates to previous, counter-intuitive findings which suggest that, although people are at greater risk of developing heart problems if they are overweight or obese, once a person has developed a heart condition, those with higher BMIs were less likely to die than those of normal weight. Various explanations have been suggested, including the fact that once someone has developed heart problems, some extra fat is somehow protective against further health problems and death, especially as people who develop a severe and chronic illness often lose weight. However, researchers and clinicians have remained unconvinced and now, this latest research confirms that living with obesity does not offer heart failure patients any protection.
This study analysed data from 1832 women and 6567 men with heart failure and reduced ejection fraction who were enrolled in the PARADIGM-HF international randomised controlled trial taking place in 47 countries on six continents. Doctors collected data on BMI, blood pressure, body measurements, results from blood tests, medical histories and treatments.
Once analysed the data on BMI and waist-to-height ratio showed that more body fat was associated with a greater risk of death or hospitalisation for heart failure. This was more evident for waist-to-height ratio. When looking at waist-to-height ratio, the researchers also found the top 20% of people with the most fat had a 39% increased risk of being hospitalised for heart failure, compared to people in the bottom 20% who had the least fat.
John McMurray, Professor of Medical Cardiology at the University of Glasgow, who led the research, said: “Our study shows there is no ‘obesity survival paradox’ when we use better ways of measuring body fat. BMI does not take into account the location of fat in the body or its amount relative to muscle or the weight of the skeleton, which may differ according to sex, age and race. In heart failure specifically, retained fluid also contributes to body weight. Our study has clarified the true relationship between body fat and heart failure patient outcomes, showing that greater obesity is actually associated with worse not better outcomes, including high rates of hospitalisation and worse health-related quality of life.”
Professor Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow, said: “These observations raise the question as to whether weight loss might improve outcomes, and we need trials to test this. In the UK, the National Institute for Health and Care Excellence, NICE, now recommends that waist-to-height ratio instead of BMI is used for the general population, and we should support this for patients with heart failure too.”
The study is the first to look at different ways of measuring the size and proportions of patients, including BMI, but also measurements such as waist-to-height ratio, waist circumference and waist-to-hip ratio, and adjusting the patient outcomes to take account of other factors that play a role in, or predict, these outcomes, such as levels of natriuretic peptides – hormones that are secreted in the blood when the heart is under pressure.
Professor Mark Petrie, University of Glasgow, said: “It is important because the underdiagnosis of heart failure in people living with obesity is a major issue in primary care. Patients’ symptoms of breathlessness are often dismissed as due solely to obesity. Obesity is a risk factor and driver of heart failure. Whereas in the past weight loss may have been a concern for patients with heart failure and reduced ejection fraction, today it is obesity.”
The study, ‘Anthropometric measures and adverse outcomes in heart failure with reduced ejection fraction: revisiting the obesity paradox,’ is published in the European Heart Journal.
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First published: 22 March 2023