Graduation Year

2023

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

School of Aging Studies

Major Professor

Ross Andel, Ph.D.

Co-Major Professor

Hongdao Meng, Ph.D.

Committee Member

Gizem Hülür, Ph.D.

Committee Member

Victor Molinari, Ph.D., ABPP

Committee Member

Claire Murphy, Ph.D.

Committee Member

Troy Quast, Ph.D.

Keywords

aging, BMI, episodic memory, waist circumference

Abstract

Obesity has been linked to conditions including cardiovascular disease, cancer, and diabetes. While the relationship of these conditions with obesity is well-established, the relationship between obesity and cognitive function is murkier.

Study 1 examined the association between being overweight or obese and performance on tests of executive function and episodic memory. The possibility that overweight/obesity affects cognition differently in middle vs. older age was also examined. Data from 6,012 participants in the 2018 wave of the Health and Retirement Study (HRS) were used. Body mass index (BMI) and waist circumference were used as overweight/obesity measures. Neither BMI (p = .809) nor waist circumference (p = .959) were significantly associated with performance on a speed of processing task. On a test of executive function, greater BMI in older adults was associated with better performance (β = .01, p < .05). However, this positive association was not seen with middle-aged adults (p = .119). Greater BMI was also associated with improved performance on tests of episodic memory (β = .02, p < .05). The findings indicate that weight status, as measured by BMI, was positively associated with performance on tasks of executive function and episodic memory, but not processing speed. However, waist circumference was not significantly associated with performance on any of the cognitive tasks. Given the role of obesity in premature mortality, selective mortality may be one potential explanation of these finding.

In Study 2, random intercept cross-lagged panel analyses on 14,639 participants from the Health and Retirement Study sought to determine how the association between obesity and episodic memory may change over time. BMI was used as the measure of obesity. The results showed that episodic memory did show a long-term association with obesity, and that this was stronger in older adults than middle-aged adults. The results also show that the association between obesity and episodic memory evolves over time such that obesity from T1 to T2 was negatively associated with performance on tests of episodic memory in middle-aged and older adults, but from T2 onwards, increased BMI was significantly, positively associated with episodic memory task performance in older adults.

Engaging in physical activity is one pathway through which individuals can combat the harmful effects of obesity. Study 3 sought to examine whether individuals in certain weight groups received greater cognitive benefits from physical activity than others. Data from 6,012 participants in the Health & Retirement Study were used. Results indicated that in the overall sample, obese (based on BMI) adults who frequently participated in light physical activity had the highest test scores (15.18 pts), on average, compared to peers who were normal weight and exercised at the same intensity and frequency (14.99 pts). Older adults who were obese (by BMI and waist circumference) and engaged in light physical activity also had higher average test scores compared to normal weight older adults who also participated in light physical activity. These findings suggest that while being physically active is beneficial for all groups, those who are obese may enjoy greater cognitive benefits.

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