Body mass index and disability: an international analysis in middle- and high-income countries
Population ageing is accompanied by an increase in the number of people living with functional limitations that make everyday tasks more difficult, such as shopping for groceries, managing money or getting dressed independently. In this context, body mass index (BMI) is often studied as a risk factor, but less is known about how underweight and obesity translate into disability, or whether these links have changed over time.
In a recently published open-access article in Obesity Reviews, the EpiAgeing team (CRESS U1153, Université Paris Cité / Inserm) examined the association between BMI categories and functional limitations in adults aged 50 years and over, drawing on several large nationally representative surveys conducted in the United States, Europe, Korea, Mexico, India and China.
This work is original in two ways: it compares high-income and middle-income countries, and it uses two observation periods (the early 2000s and the mid-2010s), which makes it possible to see whether the rise in obesity has been accompanied by a change in its relationship with disability.
The findings have a clear message: both extremes of BMI, underweight and obesity, are associated with a higher risk of functional limitations. Compared with so-called “normal” weight, being underweight is consistently linked to a higher likelihood of difficulties in daily life, whether for practical tasks or basic self-care. This suggests greater frailty and lower physiological reserve among underweight older adults.
For obesity, the picture is more nuanced. Among men, obesity is paradoxically associated with fewer limitations in certain instrumental tasks, particularly money management, but with more difficulty performing basic physical tasks such as dressing. Among women, obesity is clearly linked to more limitations in basic activities of daily living and, in high-income countries, to greater difficulties in some mobility-related tasks such as grocery shopping or preparing hot meals.
Another important result is that these associations between extreme BMI and disability are generally stronger in high-income countries than in middle-income countries. Several possible explanations are discussed: more sedentary lifestyles, better survival with chronic diseases at the cost of more years lived with limitations, and cultural differences in how disability is reported and experienced.
Finally, although the prevalence of obesity increased markedly between the early 2000s and the mid-2010s, the strength of the association between BMI categories and functional limitations appears to have remained broadly stable over time. In other words, it is not so much the nature of the relationship that has changed, but the number of people exposed.
In summary, this study shows that preventing both underweight and obesity after age 50 is essential to limiting the burden of disability associated with ageing. It calls for prevention and management strategies tailored to sex, BMI category and country income level, so that as many people as possible can grow older while maintaining their autonomy.
By Marcos Machado-Fragua
marcos.machado@inserm.fr
Photo credit: M. Machado-Fragua – illustration générée par IA (DALL·E)
