New Study Calls Into Question Current BMI Guidelines For Older Adults
Adults aged over 70 years who are classified as overweight are less likely to die over a ten year period than adults who are in the ‘normal’ weight range, according to a new study published January 28, 2010 in the Journal of The American Geriatrics Society.
Researchers looked at data taken over a decade among more than 9,200 Australian men and women aged between 70 and 75 at the beginning of the study, who were assessed for their health and lifestyle as part of a study into healthy aging. The paper sheds light on the situation in Australia, which is ranked the third most obese country, behind the United States and the United Kingdom.
Obesity and overweight are most commonly defined according to body mass index (BMI), which is calculated by dividing bodyweight (in kg) by the square of height (in metres). The World Health Organisation (WHO) defines four principal categories: underweight, normal weight, overweight, and obese. The thresholds for these categories were primarily based on evidence from studies of morbidity and mortality risk in younger and middle-aged adults, but it remains unclear whether the overweight and obese cut-points are overly restrictive measures for predicting mortality in older people.
The study began in 1996 and recruited 4,677 men and 4,563 women. The participants were followed for ten years or until their death, whichever was sooner, and factors such as lifestyle, demographics, and health were measured. The research uncovered that mortality risk was lowest for participants with a BMI classified as overweight, with the risk of death reduced by 13% compared with normal weight participants. The benefits were only seen in the overweight category not in those people who are obese.
“Concerns have been raised about encouraging apparently overweight older people to lose weight and as such the objective of our study was to examine the major unresolved question of, ‘what level of BMI is associated with the lowest mortality risk in older people?’” said lead researcher Prof. Leon Flicker, of the University of Western Australia. “These results add evidence to the claims that the WHO BMI thresholds for overweight and obese are overly restrictive for older people. It may be timely to review the BMI classification for older adults.”
In those participants who died before the conclusion of the study, the researchers concluded that the type of disease which caused their death, for example heart disease or cancer, did not affect the level of protection being overweight had. To remove any risk of bias in participants with illnesses which caused them to lose weight, and also increased their risk of dying, the researchers contrasted subjects who were relatively healthy compared with those who had major chronic diseases or smoked and found no apparent differences in the BMI: mortality relationship.
While the same benefit in being overweight was true for men and women, being sedentary doubled the risk of death for women, whereas it only increased the risk by a quarter in men.
“Our study suggests that those people who survive to age 70 in reasonable health have a different set of risks and benefits associated with the amount of body fat to younger people, and these should be reflected in BMI guidelines,” concluded Flicker.
This study is published in the February issue of the Journal of the American Geriatrics Society.