People with at least two of the diseases—type 2 diabetes and heart disease or stroke–have double the risk of developing dementia, according to a Karolinska Institute study “Cardiometabolic multimorbidity accelerates cognitive decline and dementia progression” that appears in Alzheimer’s & Dementia.

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.

“Few studies have examined how the risk of dementia is affected by having more than one of these diseases simultaneously, so that’s what we wanted to examine in our study,” says Abigail Dove, doctoral student at the Aging Research Center, part of the Department of Neurobiology, Care Sciences and Society, Karolinska Institute.

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.

More than one cardiometabolic disease doubles the risk

The researchers extracted data from the Swedish National Study on Aging and Care on a total of 2,500 healthy, dementia-free individuals over the age of 60 living on Kungsholmen in Stockholm.

“Cardiometabolic diseases (CMDs) have been individually associated with adverse cognitive outcomes, but their combined effect has not been investigated,” write the investigators.

“A total of 2577 dementia-free participants 60 years of age or older were followed for 12 years to observe changes in cognitive function and to detect incident cognitive impairment, no dementia (CIND) and dementia. CMDs (including type 2 diabetes, heart disease, and stroke) were assessed at baseline through medical records and clinical examinations.

“Cardiometabolic multimorbidity was defined as the presence of two or more CMDs. Data were analyzed using multi-adjusted linear mixed-effects models, Cox regression, and Laplace regression.

“CMD multimorbidity was associated with cognitive decline, CIND (hazard ratio [HR] 1.73; 95% confidence interval CI 1.23 to 2.44), and its progression to dementia (HR 1.86; 95% CI 1.17 to 2.97). CMD multimorbidity accelerated the onset of CIND by 2.3 years and dementia by 1.8 years.

“CMD multimorbidity accelerates cognitive decline and increases the risk of both CIND and its conversion to dementia.”

The presence of more than one cardiometabolic disease accelerated the speed of 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.

“In our study, the combinations of diabetes/heart disease and diabetes/heart disease/stroke were the most damaging to cognitive function,” says Dove.

Prevention of a second disease important

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,” adds Dove.

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,” continues Dove.

The researchers hope in future studies to learn more about the mechanism driving this correlation by examining the impact of genetic factors and using brain imaging to see how cardiometabolic diseases might damage the brain.