Corresponding author Doctor Caterina Rosano, of Pittsburgh University in the US, said: “Our data suggest muscle adiposity plays a unique role in cognitive decline, distinct from that of other types of fat or other muscle characteristics.”
There are three types of muscle in the body: skeletal, smooth and cardiac.
As the name suggests, skeletal muscle is attached to bone and is responsible for skeletal movement.
It is this type of muscle affected by myosteatosis.
As part of the research, Dr Rosano’s team tracked 1,634 men and women aged over 70 for a decade.
Increases in thigh muscle fat in the first six years were associated with faster cognitive decline.
“If that is the case, then the next step is to understand how muscle fat and the brain ‘talk’ to each other, and whether reducing muscle adiposity can also reduce dementia risk,” she said.
There is currently no cure for dementia or Alzheimer’s disease, therefore understanding ways to prevent the conditions is key.
Without prevention methods it is predicted the number of dementia cases worldwide will triple to more than 150 million by 2050.
The study results stood after taking into account other factors such as genetic susceptibility, diabetes, high blood pressure and physical activity.
Dr Rosano said: “Obesity and loss of muscle mass are emerging as risk factors for dementia, but the role of adiposity infiltrating skeletal muscles is less clear.”
Muscle fat increases with older age and especially among black women – a group at higher Alzheimer’s risk.
Dr Rosano said: “Clinicians should be aware that regional adiposity accumulating in the skeletal muscle may be an important, novel risk factor for cognitive decline in black and white participants independent of changes to muscle strength, body composition and traditional dementia risk factors.”
It comes as a study by Belgian scientists published last month found individuals with myosteatosis were twice as likely to suffer a premature death than obese peers.
It is comparable to smoking or having type 2 diabetes – but the phenomenon has been largely overlooked, they said.
“Clinicians should be aware adiposity distribution is an important risk factor for cognitive decline, distinct from overall adiposity and muscle loss,” Dr Rosano added.