Elevated body mass index and maintenance of cognitive function in late life: exploring underlying neural mechanisms.
BACKGROUND
Obesity is associated with vascular risk factors that in turn, may increase dementia risk. However, higher body mass index (BMI) in late life may be neuroprotective. The possible neural mechanisms underlying the benefit of higher BMI on cognition in older adults are largely unknown. Thus, we used functional connectivity magnetic resonance imaging (fcMRI) to examine: (1) the relationship between BMI and functional brain connectivity; and (2) the mediating role of functional brain connectivity in the association between baseline BMI and change in cognitive function over a 12-month period.


METHODS
We conducted a 12-month, prospective study among 66 community-dwelling older adults, aged 70 to 80 years, who were categorized as: normal weight (BMI from 18.50 to 24.99); overweight (BMI from 25.00 to 29.99); and obese (BMI ≥ 30.00). At baseline, participants performed a finger-tapping task during fMRI scanning. Relevant neural networks were initially identified through independent component analysis (ICA) and subsequently examined through seed-based functional connectivity analysis. At baseline and 12-months, we measured three executive cognitive processes: (1) response inhibition; (2) set shifting; and (3) working memory.


RESULTS
Obese individuals showed lower task-related functional connectivity during finger tapping in the default mode network (DMN) compared with their healthy weight counterparts (p < 0.01). Lower task-related functional connectivity in the DMN at baseline was independently associated with better working memory performance at 12-months (p = 0.02). Finally, DMN functional connectivity during finger tapping significantly mediated the relationship between baseline BMI and working memory at 12-months (indirect effect: -0.155, 95% confidence interval [-0.313, -0.053]).


CONCLUSIONS
These findings suggest that functional connectivity of the DMN may be an underlying mechanism by which higher BMI confers protective effects to cognition in late life.
Aging, Mobility, and Cognitive Neuroscience Lab, Department of Physical Therapy, University of British Columbia Vancouver, BC, Canada ; Vancouver Health Research Institute Vancouver, BC, Canada ; Djavad Mowafaghian Centre for Brain Health, University of British Columbia Vancouver, BC, Canada ; Center for Hip Health and Mobility, Vancouver General Hospital Vancouver, BC, Canada.
Chun Liang
CL
Hsu
Health, Brain, and Cognition Lab, University of Iowa Iowa City, IA, USA ; Department of Psychology, University of Iowa Iowa City, IA, USA.
Michelle W
MW
Voss
Aging, Mobility, and Cognitive Neuroscience Lab, Department of Physical Therapy, University of British Columbia Vancouver, BC, Canada ; Vancouver Health Research Institute Vancouver, BC, Canada ; Djavad Mowafaghian Centre for Brain Health, University of British Columbia Vancouver, BC, Canada ; Center for Hip Health and Mobility, Vancouver General Hospital Vancouver, BC, Canada.
John R
JR
Best
Department of Psychology, University of British Columbia Vancouver, BC, Canada.
Todd C
TC
Handy
Department of Medicine, University of British Columbia Vancouver, BC, Canada.
Kenneth
K
Madden
Aging, Mobility, and Cognitive Neuroscience Lab, Department of Physical Therapy, University of British Columbia Vancouver, BC, Canada ; Vancouver Health Research Institute Vancouver, BC, Canada ; Djavad Mowafaghian Centre for Brain Health, University of British Columbia Vancouver, BC, Canada ; Center for Hip Health and Mobility, Vancouver General Hospital Vancouver, BC, Canada.
Niousha
N
Bolandzadeh
Aging, Mobility, and Cognitive Neuroscience Lab, Department of Physical Therapy, University of British Columbia Vancouver, BC, Canada ; Vancouver Health Research Institute Vancouver, BC, Canada ; Djavad Mowafaghian Centre for Brain Health, University of British Columbia Vancouver, BC, Canada ; Center for Hip Health and Mobility, Vancouver General Hospital Vancouver, BC, Canada.
Teresa
T
Liu-Ambrose
body mass index; default mode network (DMN); executive functions; mediation analysis; older adults