Severe obesity has a similar effect on life expectancy as smoking, a study has found.
The study published in the Lancet online first showed people who have a body mass index (BMI) above the ideal range of 22.5-25 kg/m2 are significantly more likely to die, with each extra 5 kg/m2 increasing overall mortality by around one third.
This means that people who have a BMI above 40 kg/m2 will die eight to ten years younger – a similar shortening in life expectancy is seen in a smoker.
The researchers analysed the relationship between BMI and the risk of dying from particular diseases using data from 57 prospective studies involving 900,000 people.
Mortality was lowest in the BMI range 22.5-25 kg/m2 . Each additional 5 kg/m2 translated into the following increases in mortality: overall 30%; heart disease, stroke, and other vascular disease 40%; diabetes/liver disease/kidney disease 60-120%; cancer 10%; lung disease 20%.
Moderate obesity (BMI 30-35 kg/m2 ), which is now common, reduced survival by between two and four years. Severe obesity (40-45 kg/m2 ), which remains relatively rare, reduced survival by eight to 10 years, comparable to the effects of smoking.
Dr Gary Whitlock, Clinical Trial Service Unit, University of Oxford, UK, said: ‘‘In countries like Britain and America, weighing a third more than the optimum shortens lifespan by about 3 years. For most people, a third more than the optimum means carrying 20 to 30 kilograms (50 to 60 pounds, or 4 stone) of excess weight. If you are becoming overweight or obese, avoiding further weight gain could well add years to your life.’’
The study also found there was also a higher death rate among those who had a BMI well below the optimum range. This was due mainly to smoking related diseases, but the researchers said further study is required to fully understand the reasons behind this relationship.