5 conditions outside the brain that may increase dementia risk

For more than 50 years, scientists have searched for answers to Alzheimer’s disease — one of the most devastating forms of dementia.

Traditionally, Alzheimer’s has been viewed as a disease that begins and progresses entirely within the brain. On the surface, that makes sense.

But growing evidence suggests the story may be more complex.

Researchers are increasingly exploring how conditions throughout the body — from metabolic disorders to sensory loss — may influence brain health and dementia risk.

Dementia may involve more than just the brain

A large systematic review of more than 200 studies, conducted by researchers at Sun Yat-Sen University in China, found that up to one-third of dementia cases may be associated with diseases outside the brain.

Importantly, this doesn’t mean these conditions directly cause dementia. Instead, they appear to contribute to overall risk at the population level.

Still, the findings add to a growing body of research suggesting that Alzheimer’s and other forms of dementia may be influenced by whole-body health — not just what happens in the brain.

This idea isn’t entirely new.

In recent years, scientists have proposed several theories about Alzheimer’s, including:

• Immune system involvement, where chronic inflammation may play a central role
• Metabolic dysfunction, sometimes referred to as “type 3 diabetes”
• Disruptions in energy production within cells

While none of these theories fully explain Alzheimer’s on their own, they highlight an important point:
Dementia is likely a complex, multi-system condition.

Hidden risk factors linked to higher dementia risk

The Chinese review identified 16 peripheral (non-brain) conditions associated with increased dementia risk.

Among the most consistently linked were:

Gum disease

Chronic inflammation from periodontal disease may contribute to systemic inflammation, which has been associated with cognitive decline.

Chronic liver disease

Advanced liver disease can lead to a buildup of toxins such as ammonia in the bloodstream, which may affect brain function.

In some cases, this can result in hepatic encephalopathy, a condition that can mimic dementia symptoms — but is distinct from Alzheimer’s and may be reversible with treatment.

Hearing loss

Hearing loss is one of the strongest modifiable risk factors for dementia.

Studies show that people with hearing loss may experience a 30% to 40% faster rate of cognitive decline over several years.

One explanation is that the brain must work harder to process sound, leaving fewer resources available for memory and thinking.

Vision loss

Poor vision has also been linked to increased dementia risk.

In some cases — such as cataracts or uncorrected vision — treatment may help reduce that risk, though not all causes of vision loss are reversible.

Type 2 diabetes

Type 2 diabetes can damage blood vessels, including those in the brain, increasing the risk of vascular dementia.

It may also contribute to inflammation and impaired insulin signaling in the brain.

What this means for protecting your brain

While these conditions don’t directly cause Alzheimer’s, they highlight something important:

Brain health is deeply connected to overall health.

Addressing modifiable risk factors — like managing blood sugar, protecting hearing, treating vision problems, and reducing chronic inflammation — may help lower the risk of cognitive decline over time.

As the study authors noted, targeting these broader health conditions could help reduce the overall burden of dementia.

The bottom line

Dementia is no longer viewed as a condition that exists in isolation within the brain.

Instead, research increasingly shows it may be influenced by what’s happening throughout the body.

That means one of the most powerful ways to protect your brain may be surprisingly simple:

Take care of your whole-body health.

Sources:

Population attributable fractions of a wide range of peripheral diseases for the burden of dementia — Nature Human Behavior

One in Three Dementia Cases Is Linked to Disease Outside The Brain — Science Alert