What's bad for the heart can also hurt the brain and put middle-aged people at higher risk for dementia later in life, researchers say.

Those with diabetes, high blood pressure, high cholesterol or who smoke are not only at higher risk of heart disease, but also dementia, a new study suggests.

Investigators studied medical records of nearly 9,000 men and women aged 40 to 44 in California from 1964 to 1973.

Some risk factors seem to affect the heart and brain in similar ways.

After taking a second look at the patients' records from 1994 to 2003, the researchers found 721 patients had been diagnosed with dementia, which can affect memory, concentration and judgment.

They concluded each of the four cardiovascular risk factors was associated with a 20 per cent to 40 per cent increased risk of dementia, after factoring out age, race, gender and education, compared to those without any of the risk factors.

The risk factors also add up, and people with all four risk factors have more than double the risk of Alzheimer's, according to the study.

If people with high cholesterol or blood pressure are identified before they are in their 50s, they may be able to reduce their dementia risk through diet and lifestyle changes, said study author Rachel Whitmer, from the Kaiser Permanente Division of Research in Oakland, Calif.

More research is needed to show if reducing the heart disease risk factors does in fact help dementia risk, as well.

Previous studies have reported an association between the heart disease risk factors and dementia. Those findings are strengthed by the large size of this study and its follow-up period.

Researchers suspect there is a connection between the two diseases since what happens to blood vessels in the heart resembles the fate of blood vessels in the brain.

To prevent dementia, the Alzheimer's Association recommends:

• Keeping mentally active: read, take a class, work crossword puzzles, play games.
• Stay physically active: walk, bike, jog, garden, practise tai chi or yoga.
• Remain socially involved: volunteer, take a dance class, travel.
• Follow a healthy diet: eat dark-skinned fruits and vegetables, fish and nuts.

The study was funded by the U.S. National Institutes of Health and appears in the Jan. 25 issue of Neurology.