Large waist circumference may be a risk factor for obesity-related dementia

A new study has shown that visceral obesity may be associated with an increased risk for dementia among older individuals.

The researchers also found that waist circumference may be a more reliable indicator of abdominal visceral fat level than body mass index (BMI).

The study is the first to examine the link between waist circumference and dementia incidence among a large population of older people.

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"
Corresponding author Hye Jin Yoo, Korea University Guro Hospital.

Previous studies examining dementia risk in relation to body fat

One 2015 large study involving almost 2 million people from the United Kingdom Clinical Practice Research Datalink found that the incidence of dementia fell for every increasing category of BMI. Two Mendelian randomization studies found no link between obesity and dementia.

However, the authors of the current study say BMI is not considered a reliable measure of adiposity because it fails to distinguish between lean body mass and fat. Waist circumference may be a better measure for predicting potential cognitive impairment among older adults.

A two-year follow-up study of older patients with diabetes found an association between central adiposity measured by waist circumference and cognitive decline. Another study found a correlation between waist circumference and overall cognition in older women with type 2 diabetes.

According to a 2018 study published in the British Journal of Nutrition that included 5,186 people aged 60 years and older, larger waist size was associated with lower performance in tests of mental abilities such as attention and visuospatial skills. Larger waist circumference was also associated with lower scores on memory tests.

The researchers involved in that study suggested that excess abdominal fat may trigger inflammation and increase levels of C-reactive protein, which has previously been associated with an increased risk for dementia.

The current study

In a study aiming to establish what classifies as a healthy waist circumference, researchers used the Korea National Health Insurance Service program to examine the relative risk of dementia associated with waist circumference and BMI. The program enrolled almost all Korean people who took part in routine health examinations twice a year.

The study included 872,082 people aged 65 years or older who had their health examined between January 1, 2009, and December 31, 2009. The participants were followed from baseline until they developed dementia, died or until December 31, 2015.

Participants were asked about their age, alcohol intake, smoking status and how much they exercised. Health insurance premiums were used as a representation of income level. Any history of diagnosed cardiovascular disease, high blood pressure, and diabetes was also taken into consideration.

The standardized health examinations included a measure of BMI (by weight in kilograms divided by height in meters squared) and waist circumference measured at the narrowest point between the lower rib cage and iliac crest on minimal respiration.

Since BMI during later life can be confounded by health conditions and concealed by diseases present at baseline, the authors worked out a hazard ratio for dementia after adjustment for a scoring system of underlying comorbidity called the Charlson Comorbidity Index (CCI).

This scoring system was divided into two categories, with a score of zero representing the absence of comorbidity and a score of one indicating the presence of at least one comorbid medical condition.

Larger waist size was linked to increased risk of dementia

As reported in the journal Obesity, the team found that men with a waist circumference of 90cm or more and women with a circumference of 85cm or more were at a significantly increased risk for dementia, after adjustment for potential confounders including BMI, cholesterol level, liver function, blood pressure and a range of lifestyle factors.

On examining the association between BMI and dementia among participants who were underweight, the team identified a significant increase in dementia risk, compared with people who were of normal weight, after adjustment for comorbid conditions and lifestyle factors.

Dan Bessesen from the University of Colorado School of Medicine, who was not involved in the study, says: "This study does not let us know why there is this discrepancy but may point to the different roles of subcutaneous fat versus visceral fat in the development of dementia with subcutaneous fat being protective and visceral fat having harmful effects.”

He also added that BMI may be a better representation of lean body mass in older individuals and the association between BMI and dementia could be more a result of the negative health effects of sarcopenia  ̶  the reduction in skeletal mass and strength that occurs as people age.

The study findings should be confirmed in other populations since it only included Asian individuals. However, it does suggest that visceral obesity may be linked to a greater risk of developing dementia.

High waist circumference associated with an elevated risk of obesity-related dementia. Eurekalert. Available at: https://www.eurekalert.org/pub_releases/2019-11/tos-hwc103119.php​.