A body mass index over 25 is normally considered unhealthy, but a study of more than 27,000 people in China suggests that may not be the case for older age groups
BMI scores estimate whether someone is a healthy weight
Clynt Garnham Medical / Alamy
People over 80 whose body mass index is higher than currently recommended have a lower mortality rate, a large-scale analysis in China has found. The findings suggest that weight guidelines should be changed for this age group.
BMI scores are used to estimate whether or not someone has a healthy weight. It is based on a person’s height and weight, and most guidelines suggest that someone with a score above 25 is overweight, while those with scores above 30 are considered obese.
These guidelines are largely based on measurements taken from younger age groups, says Xiaoming Shi at the Chinese Center for Disease Control and Prevention in Beijing. As the world’s population ages, it is important to ensure that these recommendations make sense for older age groups too, he says.
AdvertisementShi and his colleagues studied mortality risk in more than 27,000 people over the age of 80 across China from 1998 onwards. The participants had an average age of 93 when they enrolled in the study and they were followed up until 2018 or their deaths.
Previous analyses have found a link between higher BMI scores in older age groups and a lower mortality rate, but this is the first study to look at this question with such a large sample size.
In this analysis, the researchers found that the optimal BMI for the over-80s was around 29. This was largely driven by a lower risk of death from non-cardiovascular causes such as cancer or respiratory disease. This group also had a lower risk of death from cardiovascular diseases, but the relationship was weaker.
Even those with a BMI in the “obese” range, between 30 and 35, had a lower mortality rate than those in the 20 to 25 range.
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The team accounted for several factors, including socioeconomic status, education background and whether a person smoked.
Shi says it is unclear why a higher BMI is linked with a lower mortality rate, but speculates that it may be due to these people having a more nutritious diet. He also notes that, in general, the BMI scores of this population were lower than those found in the West. Over 40 per cent of the over-60s in the US are obese. “Our findings may not be generalisable to other age groups and ethnic groups,” he says.
“This study highlights the importance of taking age into account when considering the relation between BMI and mortality or other health risks,” says Louise Baur at the University of Sydney. She says this study can’t tell us exactly why being overweight may be linked to better health outcomes in the over-80s, but agrees that it may be due to better nutrition.
“While BMI is an accessible and affordable way to screen a person’s health, it shouldn’t be relied on as a single measure of health,” says Nicholas Fuller, also at the University of Sydney. “BMI is based on body weight, but a person’s disease risk is linked to body fat, not weight. It is more important to focus on measures that tell us more about fat in the body and where it’s distributed, such as waist circumference, to get a better understanding of health and risk.”
Journal reference: Nature Aging, DOI: 10.1038/s43587-022-00201-3
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A Few Extra Pounds May Be a Plus in Old Age, Researchers Say Jan. 28, 2010 -- People who carry a few extra pounds after age 70 tend to live longer than people who don’t, new research finds. Overweight older adults who took part in the Australian study had a clear survival advantage over those who were normal weight, underweight, or
obese. The findings suggest that the widely accepted body mass index (BMI) weight guidelines may not be particularly useful after age 70, lead researcher Leon Flicker, PhD, of the University of Western Australia tells WebMD. He says elderly people who don’t have health conditions like diabetes or osteoarthritis, which are caused or exacerbated by carrying extra pounds, may be better off being
overweight. “Unless they have these conditions, there is not much reason to tell people in their 70s and beyond to lose weight if they are not obese,” he says. The study is not the first to suggest that carrying some, but not too much, extra
weight may increase longevity. Last summer, researchers in Canada reported the same findings after analyzing data from more than 11,000 adults followed for more than a decade. In that study, people who met the criteria for being overweight were 17% less likely to die compared to people of normal weight. In the newly reported research, overweight study participants in their 70s followed for up to 10 years had a 13% lower risk of death than participants
classified as normal weight. BMI is calculated by dividing a person’s weight (in kilograms) by the square of their height (in meters). A body mass index of 18.5-24.9 is considered normal, a BMI of 25 to 29.9 is considered overweight, and a BMI of 30 or more is considered obese. Based on BMI scores, a 5-foot, 7-inch adult would be considered: Obese and normal-weight study participants had a similar risk of death over the 10 years of follow-up. Underweight study participants had the highest risk of death, even after the researchers adjusted for the wasting effects of disease.Elderly Benefit From Extra Weight
Women who were sedentary were twice as
likely to die as women who got regular exercise, regardless of BMI.Exercise Lowered Death Risk
The effect was seen in men, but to a lesser degree. A sedentary lifestyle was associated with a 28% increase in death among men.
The study appears in the February issue of the Journal of the American Geriatrics Society.
“There is a lot we can’t really explain in our findings, and the fact that a sedentary lifestyle seemed to be more risky for women than men is one of them,” Flicker says.
Flicker believes the BMI thresholds for overweight and obese are too restrictive for older people, and he says it may be time for the World Health Organization to change the guidelines to reflect the findings from his and other studies.
Geriatric medicine specialist Thomas Yoshikawa, MD, of UCLA’s David Geffen School of Medicine, agrees.
“From a hard science point of view it may be a bit premature, but my own personal belief is this is something we should carefully consider,” he tells WebMD.
Yoshikawa says as many as two dozen observational studies suggest that carrying a few extra pounds is beneficial for people in their 80s and older.
Although extra pounds clearly add to the risk for chronic diseases like heart disease and diabetes earlier in life, they may actually give older people extra reserves to recover from stresses like surgery or pneumonia, he says.
“I would rather have an elderly patient who is in relatively good health and is close to normal weight gain five or 10 pounds than lose five or 10 pounds,” he says.