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Body Weight and Mortality:What is the optimum weight for a longer life?



Clinical bottom line: If your body mass index (BMI) is too large, then you have a significantly increased risk of dying. Lose weight for a longer and better life.

The risk of death associated with being overweight is well known. As more men and women are becoming overweight, this timely investigation quantifies that risk and examines whether it is the same for the underweight.

Message

This large study found optimum body mass indexes to be between 23.5 and 24.9 for men and 22.0 and 23.4 for women. As body mass index increased, risk of death increased. Men and women, with body mass indexes of 40.0 or higher, increased the risk of death by 250% and 200% respectively. In contrast, underweight men and women, with body mass indexes of 18.5 or lower, increased the risk by 26% and 36% respectively.

Study

In 1982, 1,046,154 participants (who had to be at least 30 years old) from the US Cancer Prevention II Study completed questionnaires. Items included demographic characteristics, personal and family history of disease, height and weight. Out of 457,785 men and 588,369 women, 113,517 men and 88,105 women died during 14 years of follow up (a total of 201,622 deaths).

Body mass index, an index of weight adjusted for height, was calculated (weight [kg] divided by height [m] squared). The World Health Organisation classifies body mass index as: normal 18.5 to 24.9; grade 1 overweight 25.0 to 29.9; grade 2 overweight 30.0 to 39.9; and grade 3 overweight 40.0 or higher.

The association between body mass index and risk of death from all causes was examined in all participants according to smoking status and history of disease. Healthy non-smokers (84,376 men and 217,857 women) were further examined to see whether this association varied according to age, race or cause of death. (Non-smokers had never smoked).

Results

All Participants

Obesity was most strongly associated with an increased risk of death among non-smokers with no history of disease. Leanness was most strongly associated with an increased risk of death among smokers (current or former) with a history of disease.

Death from all causes was lowest among non-smokers with no history of disease and highest among smokers (current or former) with a history of disease.

Non-smokers with No History of Disease

Lowest death rates from all causes were found at body mass indexes between 23.5 and 24.9 in men and 22.0 and 23.4 in women (Figures 1 and 2).

As body mass index increased, risk of death increased from all causes and at all ages (but less so for black men and women). At body mass indexes of 40.0 or higher, white men were two and half times more likely to die (relative risk 2.58, 95% confidence interval 1.64 to 4.06) and white women were twice as likely to die (relative risk 2.00, 95% confidence interval 1.69 to 2.36).

There were much smaller increases in risk among underweight men and women. At body mass indexes of 18.5 or lower, white men and women increased the risk of death by 26% and 36% respectively (relative risk 1.26, 95% confidence interval 1.02 to 1.56; relative risk 1.36, 95% confidence interval 1.25 to 1.48).

Cardiovascular disease was the most common cause of death in the overweight, especially in men. With body mass indexes of 35.0 or higher, men nearly trebled the risk of death from cardiovascular disease (relative risk 2.90, 95% confidence interval 2.37 to 3.56).

Comment

This large study quantifies the association between body mass index and risk of death. This is valuable information for health promotion. Being underweight does not carry the same risk of death as being overweight. Increased deaths among the underweight were largely explained by smoking and disease. The increased risk found at all ages suggests that the optimum weights for men and women should remain the same throughout life (rather than a higher weight with increasing age).

You can calculate your BMI here .


Systematic review:

E Calle et al. Body-mass index and mortality in a prospective cohort of US adults. The New England Journal of Medicine 1999 341: 1097-1105.