People who have heart disease risk factors in middle age, including diabetes, high blood pressure and smoking, are at higher risk for dementia later in life, a large, long-term US study suggested Monday.

The study, led by Rebecca Gottesman, professor of neurology at Johns Hopkins University, and published in the US journal JAMA Neurology, analyzed the data of 15,744 people who participated in the Atherosclerosis Risk in Communities study, a project designed to investigate the causes and effects of the hardening of the arteries.

Participants, who were black or white, were aged 45 to 64 years whey they were recruited between 1987 and 1989.

Over an average follow-up of 23 years, they underwent a battery of medical examinations that included cognitive tests of their memory and thinking.

During that time, 1,516 participants were diagnosed with dementia.

Initially, when they analyzed the influence of factors recorded during the first exams about 25 years ago, the researchers found that the chances of dementia increased most strongly with age followed by the presence of APOE4, a gene associated with Alzheimer's disease.

Blacks were also found to have higher chance of dementia than whites and those who did not graduate from high school were also at higher risk.