In recent decades the overall death rate has fallen and people are living longer. However, we are constantly being told that we are, in general, overweight. How can this be? It is known that being overweight carries a risk of dying earlier. The explanation is that our efforts - largely successful - have been aimed at treating, rather than preventing, cardiovascular disease. In the meantime, we continue to increase the risk of acquiring conditions that, in the end, prove lethal. A new large study (over one million people) from the United States demonstrates, once again, that the risk of dying increases the more one is overweight.

People enrolled with the American Cancer Society's Cancer Prevention Study II were asked in 1982 to complete a questionnaire giving their height, weight and a number of personal details about their health and habits. During the next 14 years all deaths among the subjects were recorded, and verified by checking the National Death Index.

The body mass index (BMI) of each subject was used as a score indicating the degree of over- or underweight; it was calculated as the weight in kg divided by the square of the height in meters. (A 5'10" man weighing 177 lbs or a 5'4" woman weighing 147 lbs would have a BMI of about 25 kg/m².) The subjects were classified into 12 groups according to their BMI, ranging from scores less than 18.5 through scores over 40.

Out of more than one million participants (450,000 men, 590,000 women, all over 30 at enrollment), roughly 20% died during the 14-year follow-up. Because of the known increased risk of death from cardiovascular and cancer conditions in people who smoke, the main focus of attention was on subjects who had never smoked and those who had no history of other serious diseases. This group comprised almost one-third of the total.

Mortality rates were compared for each set of BMI scores in the nonsmoker, healthy group. This group of subjects showed quite clearly the risks of being overweight. The lowest death rates for men were at BMI scores of 23.5 to 25, and for women at scores of 22 to 23.5. These BMI values were therefore regarded as a "baseline" against which other BMI scores could be measured.

Men who had a BMI above 40 (i.e. they were really obese) were 2.7 times more likely to die during the 14-year period than men with the baseline BMIs. In women, those with BMIs above 40 were 1.9 times as likely to die as those with baseline BMIs. Although the risks of overweight were a bit less pronounced in smokers and nonsmokers with a history of disease or weight loss, they were still quite apparent. It was also shown that the risk of dying increased with very low BMI levels (i.e. below 18.5). This has been observed before, but the reasons for it are not entirely clear. It was previously suggested that thin people were at greater risk because of other diseases associated with their low weight, but that was not the case for the nonsmoker-healthy group in this study, who also showed a slightly increased risk if they were very thin.

Interestingly, black women with high BMI levels (over 40) had a much lower risk of dying than white women - the risk for white women was 2 times, but for black women only 1.2 times the baseline risk.

In men who had never smoked and had no history of disease a high BMI was most likely to foretell death from cardiovascular disease (e.g. heart attack, heart failure, stroke). There was a significant increase in the risk of cardiovascular death for those with BMIs over 25 (women) or 26.5 (men). The chances of dying from cancer were also increased with high BMI values, reaching 1.8 times the baseline risk with BMIs over 40.

Other studies have found the same sort of effects of overweight on the death rate. The most recent large US study reported covered analysis of a period that was actually 20 years earlier than the present one - 1960 to 1972. The results were very similar. The bottom-line is that the chances of dying are significantly increased if there is clear evidence of overweight.

Recent surveys have shown that, in the United States, nearly a third of adults have BMIs between 25 and 30, and a further 20% have BMIs over 30. In other words, over half the USA adults are sufficiently overweight to be at an increased risk of dying.

While these findings were obtained in an affluent developed country, other developed countries are probably not far behind, and may not be fully aware of the positive benefits of healthy eating and plenty of physical exercise. The US way of life involving fast foods and excessive leisure time spent in front of a monitor -TV or Internet surfing - fosters the likelihood of overweight. Habits are set early in life, and by middle age it is hard to correct them. However, as in many steps to improve your health, it is better late than never. Other pages on this site give good advice on how to improve your personal situation in this respect.

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