Carrying excess fat in 2 body areas may increase dementia and Parkinson's risk

• Neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease are increasing worldwide.
• Studies suggest that people with obesity are at greater risk of developing both Alzheimer’s and Parkinson’s disease.
• Now, a study has found that where the excess weight is carried may have a greater impact, with high levels of upper arm and belly fat increasing the risk of both conditions.
• The researchers suggest that improving body composition could help reduce the risks.

The number of people with neurodegenerative diseases is increasing rapidly. A 2022 analysis estimated that by 2050, around 153 million people will be living with dementia worldwide. Parkinson’s disease, the second most common neurodegenerative disorder, now affects over twice the number it did in 1990, with more than 6 million people living with the condition in 2016.

Some of the increase is due to increased lifespans, but studies show that other factors, such as obesity and lack of physical activity may also increase the risk of developing dementia. Both obesity and lack of physical activity also increase the risk of Parkinson’s. In contrast, maintaining a healthy weight and exercising may diminish the risk .

Now, a study using data from the UK Biobank has found that it is not only extra weight but where that weight is carried on the body that may influence the risk of neurodegenerative conditions.

In the study, published in Neurology, the medical journal of the American Academy of Neurology, the researchers suggest that extra belly and upper arm fat may increase the risk of these conditions, whereas increased muscle mass could decrease the risk.

“The study used a large cohort from the UK Biobank with comprehensive measurements and long follow-up, but it is observational and mostly included white participants, limiting generalizability. The potential for reverse causation and confounding factors should be considered, making the findings suggestive rather than definitive.”

— Ryan Glatt , CPT, NBC-HWC, senior brain health coach and director of the FitBrain Program at Pacific Neuroscience Institute in Santa Monica, CA, who was not involved in the study.

Higher risk with both belly and upper arm fat

Researchers analyzed data from 412,691 people, who were followed for an average of nine years. During the study, 8,224 people developed neurodegenerative diseases. The most common diagnosis was Alzheimer’s disease, with some people developing other dementias, or Parkinson’s disease.

At the start of the study, participants had an average age of 56. The researchers assessed body composition by measuring waist and hips, grip strength, bone density, and fat and lean mass.

They found that people with more belly fat (central obesity), or more upper arm fat (arm-dominant fat distribution) had an increased risk of developing neurodegenerative disorders.

Higher bone density and leg-dominant fat distribution decreased the risk, while high muscle strength appeared to protect against neurodegeneration.

These results are in line with previous research , which has suggested that people with central or abdominal obesity are at increased risk of developing dementia.

Another analysis of several studies found that weight gain, central obesity, and triceps skinfold thickness (a measure of body fat on the upper arms) were all associated with an increased risk of dementia.

Why might body composition influence Alzheimer’s risk?

“Increased upper arm and belly fat may increase the risk of [neurodegenerative disorders such as] Parkinson’s disease due to inflammation, insulin resistance, and cardiovascular health issues. However, these findings are associative, and causation cannot be firmly established. There could be confounding factors that were not fully accounted for,” Glatt explained to Medical News Today .

He also explained that cardiovascular diseases might mediate the link between body composition and neurodegenerative diseases, but that the relationship was complex:

“While managing cardiovascular health is likely beneficial, the specific contribution of body composition changes to neurodegenerative disease risk needs further investigation,” he added.

Improving body fat composition could decrease risk

This study supports findings from a previous study which found that increasing lean muscle mass can decrease the risk of neurodegenerative disorders. Experts suggest that the improved mitochondrial function in lean muscle could be responsible for the beneficial effects.

Study author Huan Song, MD, PhD, of Sichuan University in Chengdu, China, said in a press release :

“This study highlights the potential to lessen people’s risk of developing these diseases by improving their body composition. Targeted interventions to reduce trunk and arm fat while promoting healthy muscle development may be more effective for protection against these diseases than general weight control.”

However, Glatt cautioned that while higher muscle mass appeared to be associated with a reduced risk of neurodegenerative diseases:

“This could be due to better metabolic health, reduced inflammation, and improved vascular function. Yet, it remains unclear if muscle mass directly reduces risk or if it is merely a marker of overall better health and physical activity levels,” he told MNT .

More evidence that exercise benefits both body and brain

Although these findings are observational, they do reinforce previous findings that maintaining a healthy weight and body composition is beneficial for brain health.

“Improving body composition through exercise, diet, and weight management may help reduce the risk of […] neurodegenerative diseases. However, the direct impact of these interventions on neurodegeneration risk is not fully established, and such recommendations should be considered as part of broader health strategies,” Glatt advised.

With growing evidence that sedentary behavior increases the risk of dementia, the key takeaway is that any type of activity may help reduce the risk of neurodegenerative diseases.

This study suggests that, perhaps, exercise that increases muscle mass may be more effective than other forms of exercise in helping to protect against such disorders.

According to the National Institute on Aging (NIA), strength training once or twice a week can help keep both body and mind active as we age. Activities may include lifting weights, using resistance bands, or bodyweight-bearing exercises such as squats, push-ups, or yoga.

However, the NIA advises that incorporating any form of exercise into your lifestyle as you get older will help:

“Any physical activity is better than no physical activity. Even a couple minutes per day matter, and small changes lead to big improvements.”