eople who are severely obese can expect to live 10 years less than those with a healthy weight, which is equal to the effect of lifelong smoking, the largest ever investigation of the relationship between obesity and mortality has found.

The findings, which were published online in The Lancet, were generated by an analysis of data from more than one million people taking part in 57 long-term research trials around the globe, co-ordinated by Oxford University's Clinical Trials Service Unit with funding from the Medical Research Council.

The results provide further evidence of the close link between obesity and reduced life expectancy, as among the 900,000 people who were followed-up for 15 years, mortality was lowest in those who had a body mass index of 23 to 24, and highest in those with severe obesity (BMI of 40-50), who had a 10-year drop in life expectancy.

Thankfully, severe obesity is still considered to be uncommon, but moderate obesity (BMI of 30-35), which is now common among the general population, was also shown to have a significant impact on life expectancy, trimming it by three years compared to those with a normal BMI.

Obesity put patients at higher risk of death from certain types of cancer, but it is primarily its association with heart disease and stroke that drives the increased mortality rate. According to the researchers, one in four deaths from heart attack or stroke and one in 16 from are due to being overweight or obese.

“As this study demonstrates, obesity is an increasingly serious public health problem of global significance,” said Sir Leszek Borysiewicz, Chief Executive of the MRC.

And Professor Peter Weissberg, Medical Director at the British Heart Foundation, stressed that while everyone has a role to play in maintaining a healthy weight, the study “emphasises the importance of public health measures, such as the recently launched Change 4 Life campaign, as part of a raft of government initiatives that will be needed to reduce the nation's weight.”

The government has been working hard to try and reign in the current swelling tide of obesity, which could lead to around 60% of men, 50% of women and about 25% of all children under 16 being obese by 2050 at a cost of £45 billion a year, according to last year’s Foresight report.