The secret to a longer life
Keep your waist trimmer than half your height and you could significantly boost your life expectancy.
Academics are urging policymakers to adopt this simple message after finding waist-to-height ratio (WHtR) is a more accurate predictor of mortality risk than body mass index (BMI).
Researchers at Cass Business School, part of City University London, and Ashwell Associates are calling for the measurement - waist circumference divided by height - to replace BMI in primary public health screening.
It comes after the authors compared the effect of central obesity (as measured by WHtR) and total obesity (as measured by BMI) on life expectancy. Analysing more than 20-years of health data for non-smoking men and women in the UK, they found a stronger link between WHtR and mortality rates than BMI and mortality rates.
In the first study of its kind, the authors went on to quantify the number of years of life lost to obesity as measured using WHtR.
They cite the example of actors Arnold Schwarzenegger and Danny De Vito in the movie Twins. Both actors have a BMI of 34. If BMI is used as the measure of obesity both stand to lose 3.6 years of life.
However, using WHtR they calculate that Schwarzenegger (WHtR 0.48) would not expect to lose any years of life whereas De Vito (WHtR 0.71), could be expected to lose 5.8 years. This is because Schwarzenegger has a high BMI due to muscle whereas De Vito has the same level of BMI but due to fat.
According to the authors, the average 30-year-old, 5ft 10in tall man should have a waist of no more than 35in. This would put him in the healthy category. If his waist expanded to 42in or 60 per cent of his height, he risked losing 1.7 years of life and if it grew to 56in he could die 20.2 years earlier.
An average 30-year-old, 5ft 4in tall woman risked dying 1.4 years earlier if she let her waist increase from half her height, 32in, to 60 per cent of her height, 38.4in. If her waist increased to 51in, she could die 10.6 years earlier.
Professor Les Mayhew of Cass Business School said the latest findings highlighted the need for an urgent review of how obesity is measured.
"There is now overwhelming evidence that government policy should place greater emphasis on WHtR as a screening tool," he said. "Current UK policy tends to be restricted to BMI and, to a lesser extent, waist circumference. Focusing on WHtR, which is more globally useful than waist circumference, will identify those with central obesity and ensure resources are focused on those most at risk."
Cass Business School's Professor Ben Rickayzen added: "The use of WHtR in public health screening, with appropriate action, could help add years to life."
Dr Margaret Ashwell OBE, Director of Ashwell Associates, and a visiting academic at Oxford Brookes University, said: "This latest study on years of life lost further supports the very simple global message: "Keep your waist circumference to less than half your height"."