A study exploring the effect of both high BMI (body mass index) and greater waist circumference on all-cause mortality for over-65s found that a BMI indicating overweight was linked to a 46% reduction in the risk of all-cause mortality for males and that class I and class II obesity are associated with a 51% lower risk.
Having an underweight BMI or being a normal weight with a high waist circumference were associated with a higher risk of all-cause mortality in both men and women, according to the findings, led by the University of Rhode Island, USA, and published in Journal of the American Geriatrics Society.
Medical News Today reports that in addition, the study found that a high waist circumference in men was associated with a 24% higher risk of all-cause mortality, compared with people with a healthy waist size. A similar effect was seen in women.
A higher waistline measurement often indicates problematic body fat around the kidneys, liver, heart, pancreas, and digestive organs.
The study incorporated data from a cohort of 6 905 individuals aged 65 and older, from 2011 to 2024.
BMI and obesity paradox
A person’s BMI is a numerical value derived from their height and weight as a means of predicting their amount of body fat. Body fat, in general, is linked to health issues.
BMI values are associated with body-type descriptors, including the class I and II categories of obesity cited in this study, as well as underweight, healthy, and overweight.
However, BMI alone is not necessarily an indicator of health. For example, a short, muscular person may have a high BMI while being in excellent health.
“It has long been recognised that BMI is not an ideal measure, and that a high waist circumference, which typically indicates truncal obesity, is a better predictor of mortality risk,” said Mir Ali, MD, who is medical director of MemorialCare Surgical Weight Loss Centre at Orange Coast Medical Centre in California, and who was not involved in the study.
In addition, a loss of muscle mass and bone mineral density that may occur with age can result in a lower BMI. This means a higher BMI may indicate better muscle mass and bone density.
Older people with illnesses or chronic conditions may also have lost weight, resulting in a lower BMI, which may be reflected in the study.
“Patients with class I or II obesity and a normal waist circumference typically carry most of their weight in their hips and thighs, maintaining a relatively normal torso. Those who carry their weight in the lower body probably experience less impact on their internal organs,” added Ali.
Why being underweight may also be a risk
Some of the study’s results are surprising, as they indicate other factors may be at play.
“There are some surprises, especially with the paradox of the seemingly protective effect of class I and class II obesity on male mortality independent of waist circumference,” said Jayne Morgan, MD, cardiologist and VP of Medical Affairs for Hello Heart, who was also not involved in the study.
“In older adults, some weight may actually be protective,” she added. “In fact, this may actually be less of a healthy state and more of an indicator of less frailty, less debilitating illness, and lack of terminal illnesses that often portend severe weight loss.
“More weight, therefore, seems to confer a survival advantage,” she said.
Morgan also touched on the health risks associated with being underweight.
“The study lends further evidence that being underweight, regardless of waist circumference, portends the highest mortality risk,” she said. She considers this especially important in the era of potential GLP-1 abuse and body dysmorphism, especially among women.
Why increasing waist size may be a concern
The study’s finding of an association between high waistline measurements and increased mortality is less surprising.
Morgan warned that a waist increase of 5cm–7cm in perimenopausal and menopausal women may be especially concerning.
“It raises the spectre of increased cardiometabolic risk and all of its inherent health challenges, including increased insulin resistance, increased cholesterol, pro-inflammatory state, and increased cardiac and stroke risk.”
Waistline circumference is derived by measuring the waist between the lower rib and the iliac crest, the upper border of the buttocks.
A high waistline circumference is defined as about 100cm or more in men and about 88cm or more in women.
Where BMI falls short, especially for women
Morgan observed that the study found that class I and II obesity did not confer a significant mortality advantage in females. “However, interestingly, being overweight did.”
She said BMI can be especially misleading as a marker of female health, noting that several high risk body types “fly under the radar” using BMI.
She cited the “skinny fat” female: “This is the female with a normal weight, and normal BMI, but a fat redistribution from the hips to the abdomen. This increased visceral fat carries a higher metabolic burden and higher cardiovascular risk, but the woman is classified as normal despite the increased waist circumference.”
She also reported that heart-transplant BMI guidelines often wind up excluding black women.
“Many of these women exhibit the healthier body fat distribution of a smaller waist circumference and rounder hips,” she said. “This pear-shaped body for females, with weight being carried in the bottom and hips, is the healthier distribution, yet many have been denied heart transplants in part because of this metric.”
Study details
Time-Varying Body Mass Index, Waist Circumference and All-Cause Mortality in US Adults Aged 65 or Older
Furong Xu, Jacob Earp, Bryan Blissmer et al.
Published in Journal of the American Geriatrics Society on 19 August 2026
Abstract
Background
This study examined associations of body mass index (BMI) category and waist circumference (WC) independently and in tandem on all-cause mortality risk among US adults aged ≥ 65 years.
Methods
The present study utilised 14 years of longitudinal data (2011–2024) from 6905 participants in the National Health and Ageing Trends Study. Cox proportional hazards models were used to estimate the hazard ratios (HRs), adjusted for baseline age, race, education, annual income, smoking status, and homebound status.
Results
Compared with normal weight, overweight males (HR, 0.54 [95% CI, 0.45–0.66]) and males with class I and II obesity (HR, 0.49 [95% CI, 0.37–0.65]) had lower mortality risk. High WC was associated with greater mortality risk in males (HR, 1.24 [95% CI, 1.07–1.44]). Similar patterns were observed in females. In joint BMI-WC analyses, overweight regardless of WC status and class I and II obesity with high WC were associated with lower mortality risk among males. Being underweight, regardless of WC status, and having normal weight with high WC were both associated with higher mortality risk in both sexes.
Conclusions
These findings highlight the adverse association of central adiposity and the limitations of BMI-only classification for mortality risk stratification in older adults.
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