In older adults, body mass index (BMI)-adjusted waist circumference is positively associated with the incidence of dementia, according to study results published in Obesity.
Previous studies exploring the association between obesity and dementia have had inconsistent results. However, most of these studies have focused on BMI and dementia, with limited research using waist circumference as a measure, a more accurate indicator of abdominal visceral fat than BMI.
The goal of the current study was to compare the risk for dementia associated with waist circumference and BMI and to better understand the interaction between waist circumference and dementia according to BMI categories.
The study was based on patients included in the Korean National Health Screening Examination database, focusing on individuals aged ≥65 years with a BMI between 15 and 40 kg/m2 who did not have a diagnosis of dementia within 1 year.
Of 872,082 patients (397,517 men, mean age 70.4±4.7 years), average BMI was 24.1±3.1 kg/m2 and average waist circumference was 83.7±8.4 cm. The primary outcome was incident diagnosis of dementia during follow-up.
Increased waist circumference was associated with increases in BMI, systolic and diastolic blood pressure, fasting blood glucose, aspartate aminotransferase and alanine aminotransferase levels, and low-density lipoprotein and total cholesterol levels, along with an increase in the prevalence of diabetes, hypertension, and cardiovascular disease.
During a median of 6.47 years of follow-up, 114,024 patients (13.1%) were diagnosed with dementia. After adjustment for BMI and several other factors, the risk for dementia steadily grew with increasing waist circumference categories: compared with a waist circumference of 85 to <90 cm in men or 80 to <85 cm in women, hazard ratios (HRs) for dementia increased with each 5-cm increase in waist circumference (HR, 1.06 [95% CI, 1.03-1.09] for 90 to <95 cm in men; HR, 1.63 [95% CI, 1.37-1.94] for ≥110 cm in men; HR, 1.04 [95% CI, 1.02-1.07] for 85 to <90 cm in women; HR, 1.58 [95% CI, 1.36-1.84] for ≥110 cm in women).
The researchers also found that the influence of waist circumference on the risk for dementia may differ across BMI categories. Normal-weight individuals with abdominal obesity according to waist circumference (≥90 cm in men, ≥85 cm in women) had a significantly increased risk for dementia, while individuals with overweight and obesity with abdominal obesity had significantly reduced risk for dementia.
In an attempt to explore this further, the investigators performed a subsequent interaction analysis, which pointed to a significant interaction between dementia risk and waist circumference and BMI categories; the overall trend was that the risk for dementia with increasing waist circumference was positive in all groups except for the underweight and severe obesity groups.
The researchers acknowledged several study limitations, including missing data, possible survival bias, and lack of analysis on dementia subtypes.
“This study highlights the critical role of late-life central obesity in the development of dementia in older persons,” stated the investigators. “Clinicians should be aware of the utility of [waist circumference] for the assessment of obesity-related dementia risk in older persons.”
Cho GJ, Hwang SY, Lee KM, et al. Association between waist circumference and dementia in older persons: a nationwide population-based study. Obesity. 2019;27(11):1883-1891.