obesity

Belly fat in older adults linked with cognitive impairment

  • A large Irish study found that belly fat was linked to poorer cognition in older adults, while BMI was not, probably because it doesn't distinguish between muscle and fat.

Data from over 5,000 individuals found that a measure of belly fat (waist:hip ratio) was associated with reduced cognitive function in older Irish adults (60+). Body mass index (BMI), however, was found to protect cognitive function.

BMI is a crude measure of body fat and cannot differentiate between fat and muscle — the muscle component is likely to be the protective factor.

Research indicates that as we age, our fat becomes less efficient at producing a hormone that helps support the growth and survival of neurons and helps regulate their activity.

That hormone is adiponectin, which is made by fat cells, circulates in our blood and enters our brain. Inside fat cells, its production is regulated by PPAR-γ (peroxisome proliferator-activated receptor gamma).

Adiponectin is anti-inflammatory and can help regulate neuronal activity, including turning activity of some neurons up and others down. However, adiponectin is reduced in Alzheimer’s patients. Delivering adiponectin to the brain has been shown to improve cognition in mice.

Chronic stress can also decrease fat's production of PPAR-γ and adiponectin.

Fat cells become less efficient at making adiponectin in obesity, and with age. One theory is that fat cells start making inflammation-promoting signals called cytokines and this inflammation then inhibits adiponectin production.

The shift from beneficial subcutaneous fat to unhealthy fat that piles up on our bellies and around the organs inside our abdominal cavity is one that naturally occurs with age, but it is of course worse if you have a lot of excess weight around your abdomen.

Genetic variations in PPAR-γ and adiponectin as well as low blood levels of adiponectin are associated with an increased Alzheimer's risk.

https://www.eurekalert.org/pub_releases/2018-08/tcd-mob080118.php

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Smoking, hypertension, diabetes & obesity each linked to poor brain health

  • A large study has found that smoking, high blood pressure, diabetes, and obesity are each linked to more brain atrophy, and damage to white matter.
  • The more of these you have, the greater the shrinkage and damage.

Brain scans of 9,772 people aged 44 to 79, who were enrolled in the UK Biobank study, have revealed that smoking, high blood pressure, high pulse pressure, diabetes, and high BMI — but not high cholesterol — were all linked to greater brain shrinkage, less grey matter and less healthy white matter.

Smoking, high blood pressure, and diabetes were the most important factors, but there was also a compound effect, with the number of vascular risk factors being associated with greater damage to the brain. On average, those with the highest vascular risk had nearly 3% less volume of grey matter, and one-and-a-half times the damage to their white matter, compared to people who had the lowest risk.

The brain regions affected were mainly those involved in ‘higher-order’ thinking, and those known to be affected early in the development of dementia.

The associations were as strong for middle-aged adults as for older ones, suggesting the importance of tackling these factors early.

While the effect size was small, the findings emphasize how vulnerable the brain is to vascular factors even in relatively healthy adults. This also suggests the potential of lifestyle changes for fighting cognitive decline.

Although this study didn't itself examine cognitive performance in its participants, other studies have shown links between cognitive impairment and vascular risk factors, particularly diabetes, obesity, hypertension, and smoking.

https://www.eurekalert.org/pub_releases/2019-03/esoc-shb030719.php

Cognitive decline in type 2 diabetes linked to white matter hyperintensities

While type 2 diabetes has been associated with cognitive problems, the mechanism has been unclear. Now a study involving 93 people with type 2 diabetes has found that greater white matter hyperintensities (indicative of cerebral small vessel disease) were associated with decreased processing speed (but not with memory or executive function).

https://www.eurekalert.org/pub_releases/2018-09/w-rem091818.php

Reference: 

Cox, Simon R. et al. 2019. Associations between vascular risk factors and brain MRI indices in UK Biobank. European Heart Journal. doi:10.1093/eurheartj/ehz100

[4395] Mankovsky, B., Zherdova N., van den Berg E., Biessels G.-J., & de Bresser J.
(2018).  Cognitive functioning and structural brain abnormalities in people with Type 2 diabetes mellitus.
Diabetic Medicine. 35(12), 1663 - 1670.

 

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Being overweight linked to poorer memory

  • A study of younger adults adds to evidence that higher BMI is associated with poorer cognition, and points to a specific impairment in memory integration.

A small study involving 50 younger adults (18-35; average age 24) has found that those with a higher BMI performed significantly worse on a computerised memory test called the “Treasure Hunt Task”.

The task involved moving food items around complex scenes (e.g., a desert with palm trees), hiding them in various locations, and indicating afterward where and when they had hidden them. The test was designed to disentangle object, location, and temporal order memory, and the ability to integrate those separate bits of information.

Those with higher BMI were poorer at all aspects of this task. There was no difference, however, in reaction times, or time taken at encoding. In other words, they weren't slower, or less careful when they were learning. Analysis of the errors made indicated that the problem was not with spatial memory, but rather with the binding of the various elements into one coherent memory.

The results could suggest that overweight people are less able to vividly relive details of past events. This in turn might make it harder for them to keep track of what they'd eaten, perhaps making overeating more likely.

The 50 participants included 27 with BMI below 25, 24 with BMI 25-30 (overweight), and 8 with BMI over 30 (obese). 72% were female. None were diagnosed diabetics. However, the researchers didn't take other health conditions which often co-occur with obesity, such as hypertension and sleep apnea, into account.

This is a preliminary study only, and further research is needed to validate its findings. However, it's significant in that it adds to growing evidence that the cognitive impairments that accompany obesity are present early in adult life and are not driven by diabetes.

The finding is also consistent with previous research linking obesity with dysfunction of the hippocampus and the frontal lobe.

http://www.eurekalert.org/pub_releases/2016-02/uoc-bol022616.php

https://www.theguardian.com/science/neurophilosophy/2016/mar/03/obesity-linked-to-memory-deficits

Reference: 

[4183] Cheke, L. G., Simons J. S., & Clayton N. S.
(2015).  Higher body mass index is associated with episodic memory deficits in young adults.
The Quarterly Journal of Experimental Psychology. 1 - 12.

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