The first large-scale cohort study of its kind looked at the link between waist circumference in later life and the risk of dementia in a population of older Asian adults.

senior patient talking to doctor
Could waist size predict dementia risk in older adults?

Physicians, healthcare professionals, and medical researchers tend to use body mass index (BMI) to determine if a person's weight is too high, too low, or "normal."

Despite its widespread use, BMI has its flaws — and one flaw is the fact that it does not discern between fat (adipose tissue) and muscle content (lean tissue).

For this reason, some scientists have suggested that waist-to-height ratio or waist circumference measurements may be more accurate indicators of a person's healthy weight.

When it comes to older age, however, is there any link between waist circumference and cognitive health? One 2019 study that Medical News Today reported on, for example, found a link between carrying excess weight around the stomach and experiencing brain atrophy, or brain shrinkage.

Another large study, this time from 2018, found correlations between belly fat and poorer cognitive function.

However, some of these studies looked at BMI or waist-to-hip ratio. Others have found that a higher BMI raises the risk of dementia, whereas other studies have found the opposite.

Where does the truth lie? Is there a connection between fat and brain health in older age? If so, what is the best weight measurement that indicates the risk of neurological conditions such as dementia?

New research led by corresponding author Hye Jin Yoo, an associate professor at Korea University Guro Hospital in Seoul, set out to investigate.

The findings now appear in the journal .

Studying dementia risk and weight

Yoo and colleagues examined 872,082 participants, aged 65 and over, who had taken part in the Korean national health screening in 2009.

The study followed the participants from 2009 till 2015, or until they developed dementia. During the study, the participants answered questions about their smoking status, alcohol intake, and physical activity levels.

The researchers accounted for the participants' income, history of diabetes, high blood pressure, and cardiovascular disease. They also considered BMI and waist circumference.

Yoo and colleagues adjusted for potential comorbidities using the Charlson Comorbidity Index to prevent any underlying conditions influencing BMI in older age.

Waist size may indicate dementia risk

The study revealed that the participants whose waist circumference was equal to or higher than 90 centimeters (cm) for men and 85 cm for women had a significantly higher risk of developing dementia.

This association remained when the researchers adjusted for age, BMI, blood pressure, cholesterol levels, liver health, and several other lifestyle factors.

The study also found a slightly raised dementia risk for the participants with underweight, but only after the researchers accounted for other comorbidities and lifestyle factors.

"For all the physicians who deal with geriatric medicine, obesity, and dementia, this study emphasizes that waist circumference should be considered in the assessment of obesity-related dementia risk in the elderly."

Hye Jin Yoo

Dr. Dan Bessesen, of the University of Colorado School of Medicine in Aurora, was not involved in the research but comments on its significance.

He says, "This study does not let us know why there is this discrepancy but may point to the different roles of subcutaneous fat and visceral fat in the development of dementia, with subcutaneous fat being protective and visceral fat having harmful effects."

Visceral fat is that which surrounds internal organs, and it has links with various conditions. Subcutaneous fat is visible beneath the skin.

This study was limited to an Asian population, so further studies will be necessary to replicate the findings in larger populations.