A researcher who led an Australian study that found adults aged 70 and over who are classed as overweight under the current Body Mass Index (BMI) definition are less likely to die over a 10 year period than their normal weight counterparts is calling for a revision of BMI for this group so it more accurately reflects lowest mortality risk. He suggests people who live to their 70s and beyond may have a different relationship between body fat and risks to health than younger people.
You can read about the findings of the ten-year research project online in the 28th January issue of The Journal of the American Geriatrics Society. The study was led by Winthrop Professor Leon Flicker, Director Western Australian Centre for Health and Ageing (WACHA) at The University of Western Australia.
BMI Body Mass Index (BMI) is a simple ratio of weight to height that is commonly used to classify underweight, overweight and obesity in adults: it is widely used in research and also in clinical practice, for instance in helping to explain concepts of obesity and overweight to patients.
To calculate your BMI you divide you weight in kilograms by the square of your height in metres (kg/m2). For example, if you weigh 70 kg (154 lb) and your height is 1.75 m (5 ft 9 in) your BMI is 22.9, which is in the normal range.
The current BMI thresholds defined by the WHO are as follows:
— Underweight: BMI = under 18.5,
— Normal: BMI = 18.5 to 24.99,
— Overweight: BMI = 25 and over, and
— Obese: BMI = 30 and over.
Within these there are also additional cut-off points, eg for classes of obesity and thinness.
Flicker told the press that concerns are being raised about whether older people should be encouraged to lose weight, and so they wanted to address the question:
“What level of BMI is associated with the lowest mortality risk in this group?”
For the study, Flicker and colleagues examined health and lifestyle data on 9,200 men and women who were already enrolled in the Health in Men Study and the Australian Longitudinal Study of Women’s Health.
They found that:
- Participants aged 70 and over whose BMI fell into the overweight range (as per the current WHO thresholds) were less likely to die in a 10 year period from all causes of death than counterparts whose BMI fell into the normal weight range.
- This was also the case for common causes of death such as cancer and cardiovascular disease.
- Being sedentary doubled the risk of death for women but only increased the risk by a quarter for men.
The authors concluded that:
“Overweight older people are not at greater mortality risk than those who are normal weight. Being sedentary was associated with a greater risk of mortality in women than in men.”
“The BMI thresholds for overweight and obese are overly restrictive for older people,” they wrote.
The researchers pointed out that the survival benefits were only seen in the overweight category and not in those people who were classed as obese.
Flicker told the press that:
“The study shows that those people who survive to age 70 in reasonable health (and hence participate in these studies) have a different set of risk and benefits associated with amount of body fat compared with younger people.”
According to a separate statement from WACHA, Australia is the third most obese country after the United States and the United Kingdom.
“Body Mass Index and Survival in Men and Women Aged 70 to 75.”
Leon Flicker, Kieran A. McCaul, Graeme J. Hankey, Konrad Jamrozik, Wendy J. Brown, Julie E. Byles, Osvaldo P. Almeida.
The Journal of the American Geriatrics Society, Published Online: Jan 27 2010.
Sources: WACHA, WHO.
Written by: Catharine Paddock, PhD