Neurology: The higher the weight, the lower the cognitive ability

The incidence of obesity has increased
considerably over the past few decades.
Cross-sectional data from NHANES suggests that 42 percent of adults were obese in 2018, up
from 31 percent in 2000.
Obesity is associated
with an increased risk of mortality, cardiovascular disease, stroke, diabetes and cancer.
Ethnicity is representative of socioeconomic status and allogeneic load, which may contribute to differences
in obesity prevalence.
National studies show a 50 percent obesity prevalence among non-Hispanic black adults and 42 percent
among non-Hispanic white adults.
Differences in obesity prevalence and its associated cardiometabolic outcomes are associated with lower levels of education, literacy, and financial status – risk factors for cognitive impairment and dementia (CID)5
.
The relationship between obesity and CID is unclear
.

Figure 1: Cover image of the paper

Some studies have shown no or weak positive association between obesity in middle life and CID, and obesity in later life with no or negative association with CID, possibly due to the phenomenon
of prodromal weight loss that occurred in the decade before dementia diagnosis.
The relationship between obesity and CID in black and white adults is poorly understood, and longitudinal studies of racial diversity are particularly sparse
.
The study found that the effects of vascular risk factors on the brain may differ
between black and white adults.
In particular, an increase in body mass index (BMI) over time was associated with a decrease in total brain volume in black adults, but there was no evidence of an association
with white adults.
In addition, it is uncertain
whether racial differences in obesity prevalence explain differences in CID.
Moreover, whether the association between obesity and cognitive decline is independent of the effects of obesity on blood pressure (BP) and glucose levels has not been well elucidated
.

The analysis used six different, characteristic, population-based cohort studies to provide repeated objective measures of cognition to examine whether obesity independently confers an increased risk of cognitive decline and whether race alters the association
between obesity and cognitive trajectories.
The core hypothesis is that obesity is associated with greater cognitive decline compared with normal weight, and that the effect of obesity on cognitive decline is more pronounced
in black adults compared to its white counterparts.

In this way, Emmanuel Quaye et al.
of the University of Michigan pooled data
from six cohorts of 28,867 participants without stroke and dementia (mean, standard deviation [SD]: age 61 [10.
7] years at first cognitive assessment, 55% female, 24% black, and 29% obese).

The primary outcome was annual change
in global cognitive ability.
Linear mixed-effects models were performed that included and did not include time-varying cumulative mean systolic blood pressure (SBP) and fasting plasma glucose (FPG).

In the participants' first cognitive assessment, global cognition was set as a t-score indicator (mean 50, standard deviation [SD] 10); The difference of 1 point represents a 0.
1SD difference
in global cognition in the six cohorts.
The median follow-up was 6.
5 years (25th percentile, 75th percentile: 5.
03, 20.
15).

Figure 2: Graph of paper results

They found that obese individuals had lower baseline global cognition than normal-weight individuals (intercept difference, -0.
36 [95% CI, -0.
46 to -0.
17]; P<0.
001).

This difference in baseline global cognition was reduced after accounting for SBP and FPG, but remained marginal (adjusted intercept difference, -0.
19 [95% CI, -0.
39 to 0.
002]; P=0.
05）
。 There was no difference in global rates of cognitive decline between obese and normal-weight individuals (slope difference, 0.
009 points/year [95% CI, -0.
009 to 0.
03]; P=0.
32）
。

After accounting for SBP and FPG, global cognitive decline was slower in obese individuals (adjusted slope difference, 0.
03 points/year slower [95% CI, 0.
01 to 0.
05]; P<0.
001).

There was no evidence of a relationship between race altering BMI and overall cognitive decline (P = 0.
34).

These results suggest that obesity is associated with lower initial cognitive scores and has the potential to attenuate cognitive decline
after accounting for blood pressure and FPG.

Quaye E, Galecki AT, Tilton N, et al.
Association of Obesity With Cognitive Decline in Black and White Americans.
_Neurology_.
Published online October 18, 2022:10.
1212/WNL.
0000000000201367.
doi:[10.
1212/WNL.
0000000000201367](https://doi.
org/10.
1212/WNL.
0000000000201367)