Minding your heart health when you're young could spare your brain from dementia decades later, new research confirms.

Chinese researchers looked at data on more than 450,000 older Britons. They found that people who'd already been in poor cardiovascular health before they reached the age of 45 had a 25% higher odds of developing dementia, compared to those with better heart heath.

“What surprised us most was the linear relationship between age of coronary heart disease onset and dementia," said senior study author Fanfan Zheng.

"This shows the huge detrimental influence of premature coronary heart disease on brain health,” added Zheng, a researcher at the Chinese Academy of Medical Sciences & Peking Union Medical College in Beijing.

The findings were published Nov. 29 in the Journal of the American Heart Association.

Doctors have long known that failing heart health can pose a threat to the brain, with links to poorer brain circulation and even strokes.

But does the timing of heart disease onset matter?

To find out, Zheng's group analyzed data from the UK Biobank database. They looked at the medical records of hundreds of thousands of Britons who averaged 57 years of age when they were enrolled in the Biobank.

About 12% of the participants had already been diagnosed with heart disease by the time they enrolled.

The researchers then tracked cases of new-onset heart disease and dementia over a 13-year period.

Zheng's group found an overall sharp rise in risk (36%) for dementia in folks who had heart disease, compared to those who were heart-healthy.

Heart disease upped the odds for vascular dementia (tied to restricted brain blood flow) by 78%, but it also raised the odds for Alzheimer's by 13%, the team found.

If heart disease was diagnosed relatively early in life -- at or before age 45 --the risk for dementia later rose by 25%, the researchers found.

Early-onset heart disease was also linked to a 29% higher risk of Alzheimer’s disease and a 22% increased risk for vascular dementia.

Overall, the younger a person had been diagnosed with heart disease, the higher their risk rose for being diagnosed with dementia decades later.

This was an observational study looking at past data, so it could not prove cause-and-effect.

However, “as more people live longer and are diagnosed with coronary heart disease at a younger age, it’s likely there will be a large increase in the number of people living with dementia in years to come," Zheng said in a journal news release. "Health care professionals should be aware of individuals diagnosed with coronary heart disease at a young age."