Wild new study links body part size to dementia risk

You may be able to tell how well your brain will age based on the size of one small muscle, according to a new study. 

Doctors from Johns Hopkins measured the temporalis, a thin muscle that runs from the side of your skull to the jaw joint, in over 500 healthy adults. 

They watched them over five years to monitor for signs of dementia and found those with smaller temporalis muscles were 60 percent more likely to develop dementia.

As people age, they naturally lose some amount of their muscle volume, but people with dementia tend to lose muscle mass quicker than people without the memory-robbing disease. 

So, researchers like the Johns Hopkins group have begun investigating whether they could use muscle loss as predictor for dementia. 

Normally, the disease is diagnosed after it’s become so advanced that doctor’s can do little to intervene. 

Scientists are therefore looking for a cheap, easy way to diagnose someone before their symptoms begin. Then, the hope is, that they may be able to start fighting back.  This can include by incorporating things like resistance training, exercise and better nutrition. 

Study author Dr Shadpour Demehri said: ‘These interventions may help prevent or slow down muscle loss and subsequently reduce the risk of cognitive decline and dementia.’ 

Although estimates vary, some models, like the above graph from the Alzheimer’s Association, predicts that the number of dementia cases will continue growing through 2050. This is due in part to an aging populous

Approximately 7million Americans currently live with dementia. Some predictions estimate that number will have nearly doubled by 2040 – reaching 12million people. 

Cheap methods to diagnose the condition early, so that people can act quickly to potentially prevent some of the changes associated with dementia. 

Researchers have known for a while that people with this condition begin losing muscle rapidly. 

Separate studies had suggested that the temporalis muscle can be a good predictor of how muscles will fare all over the body. 

So the Johns Hopkins researchers looked to it for their study, which was presented at the Radiological Society of North America’s annual meeting, it has yet to be published in a journal.

They studied 621 people around age 70 who were healthy when the began the study. 

Over an average of five years, they monitored their participant’s muscle structure by putting them into an MRI machine, which gives detailed images of bones, muscles and blood. 

Based on the pictures they took, they sorted people into two groups. 

A total of 131 participants were in the large muscled group and 488 participants were in the small muscled group. 

They then watched for the development of dementia, by monitoring the amount of tissue lost from the brain and having them take regular cognitive tests. 

Doctors found that those with a smaller temporalis muscle were 60 percent more likely to develop dementia, even after adjusting for factors like age.

Study author Dr Kamyar Moradi, who studies radiology at Johns Hopkins, said: ‘This is the first longitudinal study to demonstrate that skeletal muscle loss may contribute to the development of dementia.’ 

The temporalis muscle helps move the jaw, and is particularly useful in chewing. People can feel it in action by placing their hand on their temple and clenching the jaw

However, Dr Max Wintermark a neuroradiologist at University of Texas, who wasn’t involved in the research, told MedPage today that more research is needed before concluding that the temporalis muscle is a good predictor of dementia risk. 

Dr Wintermark said: ‘In this particular case, it is hard to know if muscle loss is truly a risk factor for dementia or the consequence of the processes that lead to dementia.’

Still, he agreed with the study authors that working to maintain muscle mass and cardiovascular health into older age is likely helpful in staving off dementia. 

However, working to maintain muscle mass makes sense, Wintermark agreed. 

Though research hasn’t found that exercise or other interventions can halt this deadly disease, early studies have suggested that making lifestyle changes can reduce someone’s risk and symptoms of dementia. 

In a 2024 paper from University of Washington, researchers said that early studies show that both cardio and resistance training may help make brain tissue more robust into old age. 

This in turn, could help slow the progress of dementia, buying back crucial years of normalcy. 

Dr Wintermark said: ‘In general, having a healthy lifestyle with appropriate exercise is beneficial in many ways, including maintaining one’s muscle mass.’