People with Type 2 diabetes, heart disease or stroke have double the risk of developing dementia, finds a study.

Type 2 diabetes, heart diseases (ischemic heart disease, heart failure or atrial fibrillation) and stroke, so-called cardiometabolic diseases, are some of the main risk factors for dementia.

The presence of more than one cardiometabolic disease accelerated the speed of the cognitive decline and doubled the risk of cognitive impairment and dementia, expediting their development by two years.

The magnitude of the risk was increased with a greater number of diseases, as revealed in the study published in the journal, Alzheimer's & Dementia: The Journal of the Alzheimer's Association. Prevention of diabetes and cardiovascular disease could therefore be a strategy for reducing dementia risk, suggest researchers from Karolinska Institutet in Sweden.

"In our study, the combinations of diabetes/heart disease and diabetes/heart disease/stroke were the most damaging to cognitive function," said Abigail Dove, a doctoral student at the Aging Research Centre, at the Institute. However, individuals who had just one cardiometabolic disease did not display a significantly higher risk of dementia.

"This is good news. The study shows that the risk only increases once someone has at least two of the diseases, so it's possible that dementia can be averted by preventing the development of a second disease," he added.

Dementia develops slowly over decades. It first manifests as gradual cognitive decline that only shows up in cognitive tests. It then degenerates into cognitive impairment in which the individual notices their failing memory but can still look after themselves, and finally into full-blown dementia.

The researchers extracted data on a total of 2,500 healthy, dementia-free individuals over the age of 60 living on Kungsholmen in Stockholm. The participants were then followed for 12 years with medical examinations and cognitive tests in order to monitor changes in cognitive ability and the development of dementia.

The correlation between cardiometabolic diseases and the risk for dementia was stronger in the participants who were under 78 years old. "We should therefore focus on cardiometabolic disease prevention already in middle age since the risk of cognitive failure and dementia appears higher among those who develop a cardiometabolic disease earlier in life," Dove said.