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Excess weight contributes to higher risk of death in Asians
A study of more than one million Asians has reported that those who were of a normal weight were far less likely to die from any cause than individuals whose BMI was too high or low. The study, led by Dr Wei Zheng, Ingram Professor of Cancer Research at Vanderbilt-Ingram Cancer Center, Nashville, TN, and published in The New England Journal of Medicine also concluded that there are no data to support using criteria other than BMI to define overweight and obesity among Asian subjects.
"Previous studies that evaluated the association between BMI and the risk of death have been conducted primarily in populations of European descent, and the current definition of overweight and obesity is based essentially on criteria derived from those studies," said Zheng. "The validity of these criteria in Asian populations has yet to be determined. A large proportion of Asians are very thin and the impact of a severely low BMI on the risk of death has not been well evaluated until now."
World Health Organization
The World Health Organization estimates that more than 1 billion adults worldwide are overweight and at least 300 million are obese. Fat tissue has been recognized as metabolic specialists an active endocrine organ, capable of releasing a number of biologically active factors that may contribute to obesity-related diseases, including type 2 diabetes, hypertension, coronary artery disease, stroke and several types of cancer.
The research, conducted as part of the Asia Cohort Consortium, included health status and mortality information on more than 1.1 million individuals from East and South Asia. The researchers performed pooled analyses to evaluate the association between BMI and the risk of death among more than 1.1 million persons recruited in 19 cohorts in Asia. The analyses included approximately 120,700 deaths that occurred during a mean follow-up period of 9.2 years. Cox regression models were used to adjust for confounding factors.
The main message is that people must be encouraged to maintain a normal weight: too low and too high are both unhealthy. To do this, people must eat healthily, do more exercise, and not smoke" Wei Zheng
In the cohorts of East Asians, including Chinese, Japanese, and Koreans, the lowest risk of death was seen among persons with a BMI in the range of 22.6 to 27.5. The risk was elevated among persons with BMI levels either higher or lower than that range, by a factor of up to 1.5 among those with a BMI of more than 35.0 and by a factor of 2.8 among those with a BMI of 15.0 or less. A similar U-shaped association was seen between BMI and the risks of death from cancer, from cardiovascular diseases, and from other causes.
In the cohorts comprising Indians and Bangladeshis, the risks of death from any cause and from causes other than cancer or cardiovascular disease were increased among persons with a BMI of 20.0 or less, as compared with those with a BMI of 22.6 to 25.0. There was no excess risk of either death from any cause or cause-specific death associated with a high BMI.
"The finding that the same optimal weight range is associated with the lowest risk of death both in the current study, and in previous studies involving populations of European origin argues strongly against the use of race-specific or ethnic-specific BMI cutoff points to define overweight and obesity," commented Zheng. "We should be cautious, because we looked only at mortality. What we suspect is that South Asians (with high BMI) did get CVD, but that they did not die from it because of better access to healthcare. But we believe this will change in the future. The main message is that people must be encouraged to maintain a normal weight: too low and too high are both unhealthy. To do this, people must eat healthily, do more exercise, and not smoke."
The study found, unexpectedly, that obesity among sub-continent Indians was not associated with excess mortality, said Dr John D Potter, member and senior adviser, Public Health Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA. Potter attributes this to the fact that many obese people in sub-continent India have a higher socioeconomic status and so have better access to health care.
The authors conclude that their study provides strong evidence supporting the biologic plausibility that excess weight contributes to a higher risk of death. "This confirms that most people are at a higher risk for dying early if they are obese and is a clear message not to gain weight as we age," added Potter.
The researchers examined general obesity (defined by BMI) and there are some indications that among Asians, abdominal obesity may be particularly important. Subsequently, they are now examining abdominal obesity in another study.
"Our findings capture two different aspects of a rapidly evolving pattern; severe underweight was highly prevalent in Asia in the past, and we can still observe its important impact on mortality," concluded Dr Paolo Boffetta, Professor, Mount Sinai School of Medicine, New York. "Looking into the future, however, prevention of overweight and obesity deserves the highest priority."
Data analysis for the project was conducted by the Asia Cohort Consortium Coordinating Center, which is supported, in part, by Fred Hutchinson Cancer Research Center and the National Cancer Institute.