What is the impact of being overweight?
A study conducted in Sweden spanning almost four decades has suggested that overweight persons, and not just those who were obese, may also be subjected to increased risk of premature death. It also suggested that the adverse effects of excess weight on mortality may be as significant as smoking cigarettes.
Details and Findings of Study
Published in the British Medical Journal, the study had been conducted using data from Sweden's military service conscription register, census as well as cause of death register. In all, after excluding certain persons due to incomplete data, 45,920 men were tracked for a period of 38 years; the average age of the men at the start of the study was 18.7 years. During the period, 2,897 of the men passed on.
Body Mass Index and Mortality
Having accounted for age, socioeconomic status, muscle strength and smoking, the researchers found that men who were overweight (body mass index, or BMI, from 25.0 to 29.9) during adolescence at the point they joined the Swedish military in 1969 and 1970 had a 33% higher rate of mortality during the study period, as compared with their counterparts in the normal weight range (BMI from 18.5 to 24.9). Obese men (BMI of 30 or more) had even higher risk - a whopping 114% elevated likelihood of death during the period. Similar relative estimates were obtained when smokers and non-smokers were analyzed separately. Figures also did not differ by much when smoking was not adjusted for.
Underweight men (BMI less than 18.5) did okay, although those who were extremely underweight (BMI less than 17) had 33% increased mortality, too, similar to overweight men.
Smoking and Mortality
The study subjects had declared their smoking habits when they attended mandatory military conscription tests back in 1969 and 1970. Using this information, and after adjusting for age, socioeconomic status, muscular strength and BMI, the study team also found that, compared with their non-smoking counterparts, light smokers (1 to 10 sticks of cigarettes per day) experienced 54% increased rate of mortality during the period. Not surprisingly, heavy smokers (more than 10 sticks of cigarettes each day) fared worse, suffering heightened mortality rate of 111%. Again, the figures were similar even when BMI was not adjusted for. Although the magnitude of risk increase differed across BMI categories, they featured in the same direction.
Combined Effects of Smoking and Weight
Using normal-weight non-smokers as the reference group, the relative risks of mortality of almost all the other groups were large (at least 31% higher) and highly significant. Only two groups were spared - moderately underweight non-smokers and extremely underweight non-smokers. Overweight heavy smokers experienced heightened risk of 155%, while obese heavy smokers suffered the worst, having a risk close to 5 times (4.74) that of normal weight non-smokers.
Significance of Findings - Discussion
These findings are significant in two main ways. Firstly, they suggest that persons who are overweight but not obese could also be subject to increased risk of dying early; other recent studies had been divided on whether overweight people may experience such elevated risk as compared to their healthy-weight counterparts.
According to Martin Neovius, a postdoctoral fellow at Stockholm's Karolinska Institute and the leader of the study, his team's findings confirm the discoveries of the Nurse's Health Study conducted at Harvard. With one study having looked at women and one having covered men, the two studies complement each other. "We find exactly the same in men as they did in women," he said.
The team's findings also suggest that the impact on mortality of excess weight could be as significant as smoking, a big assertion considering that smoking is widely believed to be the single most important factor for many diseases and premature death. "What we show is that for the overweight, there is a significantly increased risk of premature death, similar to smoking one to ten cigarettes a day," said Neovius.
It is possible, however, that the study exaggerates the impact of being overweight. A major limitation of the analysis is that the study subjects' weight was only known at the start of the study period, or the point at which they joined the military. Generally speaking, people put on weight as they grow older, and some of those who were overweight during adolescence may have "graduated" to obesity in adulthood. If that were the case, their increased risk of premature death would be attributable to obesity, and not to merely being overweight during their younger years. This point was raised by David F Williamson, a visiting professor at the Rollins School of Public Health at Emory University.
Obesity has become an epidemic worldwide, with rates of the condition soaring in recent decades, in particular among children. Together with smoking, these two are the major behavioral risk factors for chronic degenerative diseases and premature death in developed nations today. Neovius feels that policy makers should take note of the findings of his team's study and work towards raising awareness of the dangers of being too heavy, as well as being severely underweight.
"Anti-smoking campaigns have been very successful. But we don't have any good preventative programmes for overweight and obesity," he said, in reference to his native Sweden, although things are not very different in other countries.
"We know that health behaviors are established early on in life," he also said. This tells us that adolescents must be targeted in educational efforts. Adults, too, should note that smoking and excess weight are dangerous factors, and even more deadly when put together.
Neovius M et al. Combined effects of overweight and smoking in late adolescence on subsequent mortality: nationwide cohort study. British Medical Journal 2009;338:b496.