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Obesity as bad as smoking

The Lancet has published the results of a study conducted by the Clinical Trial Service Unit (CTSU) at the University of Oxford. The results have been reported in the general media (BBC).

This study reviewed data from 57 prospective studies involving 894,576 participants with the aim of assessing the associations between body mass index (BMI) and overall and cause-specific mortality. The studies were mainly conducted in North America and Western Europe. The average age of participants at enrolment was 46 years and 61% were male.

The study found that mortality was lowest in individuals with a BMI in the range of 22.5-25 kg/m2. Overall mortality increased by 30% for each additional 5 kg/m2 increase in BMI.

When mortality was analysed by specific causes a 5 kg/m2 increase in BMI was associated with a 40% increase in vascular mortality, 120% increase in diabetic mortality, 60% increase in renal mortality and 80% increase in hepatic mortality.

A press release issued by CTSU estimates that moderate obesity (BMI 30-35 kg/m2) reduces life expectancy by 3 years and severe obesity (BMI 40-50 kg/m2) by 10 years. A 10 year reduction in life expectancy is equivalent to that seen in lifelong smokers. It was also noted that the additional risks posed by smoking and high BMI were additive.

Action: Clinicians will find this research useful when communicating the risks of obesity to patients. These data show that a severely obese smoker is likely to have a reduction in life expectancy of 20 years.