For generations, medicine treated the heart and brain as separate domains. However, a new study suggests the two are more closely connected than we thought, especially as we age.

A 25-year study of nearly 6,000 adults found that subtle heart muscle damage in middle age predicts dementia risk decades later.

The research, known as the Whitehall study, tracked UK civil servants aged 45 to 69 and measured levels of a protein called “cardiac troponin I” in their blood. Troponin I appears in the blood when heart cells are damaged and is used to help diagnose heart attacks.

The protein is detected using a standard blood test. These tests have become more sensitive in recent years, so even very small amounts of troponin can now be detected – levels far below those seen in a heart attack – and these small changes can signal many other conditions.

In the Whitehall study, people with the highest levels of troponin I in midlife were 38% more likely to be diagnosed with dementia later in life than those with the lowest levels. These small increases don’t cause obvious symptoms, such as chest pain, but they suggest the heart is under strain even if a person feels fine.

Over 25 years, people with higher starting troponin levels were more likely to develop dementia than those with lower levels. For every doubling of troponin, dementia risk rose by 10%, even after considering age, sex, blood pressure, cholesterol, diabetes and other cardiac risk factors.

Fifteen years into the study, MRI brain scans of 641 participants showed clear differences. Those who had the highest midlife troponin levels had smaller grey-matter volume and more shrinkage of the hippocampus, the area important for memory, compared with the low troponin group. This was similar to around three extra years of ageing in the brain.

Why does heart health in your 50s foretell brain decline decades later? The answer lies in circulation.

The brain relies on a constant, rich blood supply. If the heart pumps less efficiently, or if the arteries are stiff and narrow due to atherosclerosis, the brain’s delicate network of small vessels become starved of oxygen. This chronic low-grade damage can accelerate the processes that lead to dementia.

The same study found that people with higher midlife troponin levels also experienced faster declines in memory and reasoning over time. By age 90, their cognitive performance was equivalent to that of people two years older than those with lower troponin levels.

Matters of the heart

These results fit neatly with what is already known. The 2024 Lancet Commission on dementia estimated that 17% of dementia cases could be prevented or delayed by improving cardiovascular health, through lowering blood pressure, managing cholesterol, staying active, and avoiding smoking and excess alcohol.

Likewise, an earlier analysis from the same Whitehall cohort showed that people with good cardiovascular health at age 50 were less likely to develop dementia 25 years later. Taken together, the message is simple: what’s good for the heart is good for the brain.

The two organs share a vascular network, and damage to one inevitably affects the other. Yet the long time lag uncovered by the Whitehall study suggests that troponin elevations seen up to 25 years before dementia onset, pathological processes linking the heart and brain start far earlier than first thought.

Troponin explained.

Raised troponin doesn’t guarantee dementia. Levels can fluctuate with age, kidney function or even after vigorous exercise. But as a population marker, troponin may identify people whose cardiovascular systems are already under stress while they still feel healthy.

The idea that a single blood test in middle age might one day help flag those at higher risk of cognitive decline is appealing, not as a diagnosis but as an early warning.

Medicine often divides the body into organ systems, each treated in isolation. This study reminds us that biology doesn’t respect those boundaries. A struggling heart doesn’t just affect circulation – it may, quietly and imperceptibly, change the brain’s future too.