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Obesity and life expectancy

Study
Results
Comment

Being overweight is properly regarded as being a bad thing as pointed out in a report from the National Audit Office featured in Bandolier 85. What we need, perhaps, are better ways of telling people just what effect it has both on the quality and quantity of life. A Dutch analysis of the famous Framingham study quantifies the loss of life expectancy from being overweight [1].

Study

Information from 3,457 people who were 30-49 years old in about 1950 with initial height, weight and smoking status information on entry formed the cohort. Those chosen were neither underweight nor had cardiovascular disease at entry, and had at least four years of follow up. They were classified into three groups, with BMI between 18.5 and 24.9 kg/sq metre, 25 to 29.9 kg/sq metre, and 30 kg/sq metre or greater.

The main outcome was life expectancy at 40 years of age over a follow up of 40 years.

Results

There were 728 deaths in the period of four to 28 years of follow up, and 919 deaths in the period between 29 and 40 years of follow up. The probability of death increased with each step increase in BMI. Adjustment for physical activity at baseline and education made no difference to results. Smoking status at baseline, but not sex, modified effects of obesity, and results were given for smoking and non smoking women and men.

People with a BMI of 30 kg/sq metre or more at baseline, both women and men, smokers and non smokers, lost an average of seven years of life (Figure 1). For those with a BMI between 25 and 30 kg/sq metre fewer years were lost, and significant loss of years of life was restricted to female non smokers.

Figure 1: Years of life lost from age 40, compared with BMI less than 25

After 20 years, most survivors (67%) were in the same BMI category as they were initially. Of the remainder, 27% had increased by at least one BMI category, while only 6% had fallen by at least one BMI category.

Comment

This study makes explicit the decreased life expectancy associated with obesity. Those with BMI of 30 kg/sq metre or more can expect to have seven fewer years of life than their slimmer brothers and sisters. The effect is independent of sex and smoking, but the reason cannot be gleaned from this study, but it undoubtedly stems from a number of factors, including diet and exercise.

We know (Bandolier 78) that a healthy lifestyle greatly reduces the risk of heart attack and stroke, and we know they benefit in other areas too. If being overweight is a marker of an unhealthy lifestyle, the fact that it takes years off a life should be no big surprise.

References:

  1. 1 A Peeters et al. Obesity in adulthood and its consequences for life expectancy: a life-table analysis. Annals of Internal Medicine 2003 138: 24-32.

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