The term “ dementia ” refers to several types of brain disorders that impair thought, memory, and language. Scientists estimate that up to four million Americans suffer from Alzheimer’s disease , the most common, slowly progressive form of dementia. Vascular dementia is the second most common manifestation, and is thought to be caused by a series of small strokes . Dementia usually begins after age 60, and risk goes up with age. While only about 3% of people age 65-74 have Alzheimer’s, nearly half of those age 85 and older have the disease. There is no known cure for dementia.

Cardiovascular disease (CVD) and dementia often occur together, and while the causes of dementia, particularly Alzheimer’s, are unknown, the reasons behind CVD are better understood. Therefore, scientists are very interested in learning about any connections between these two conditions, as there may be significant crossover in how they can be treated and prevented.

Diabetes, high cholesterol , high blood pressure (hypertension) , and smoking are four proven and treatable risk factors for CVD. Furthermore, they have all been associated with Alzheimer’s disease and vascular dementia. But, heretofore, no long-term research had been conducted to determine whether risk factors for CVD early in life could predict dementia years later. Without this knowledge, scientists were left to wonder if CVD actually caused dementia or if it only exacerbated existing symptoms.

New research published in the January 25, 2005 issue of Neurology sheds some light on the relationship between these conditions. Researchers reported that each of the four cardiovascular risk factors—hypertension, high cholesterol, diabetes, and smoking—if present during midlife ( before dementia is usually diagnosed), raised the risk of later dementia by 20% to 40%.

About the Study

Study investigators examined the medical histories of 8,845 members of a health maintenance organization ( HMO) in Northern California who underwent voluntary health exams between 1964 and 1973 (at ages 40-44), and were still members of the health plan and available for follow-up between 1994 and 2003 (at ages 61-83). Members were male and female, multiethnic, and all had equal access to care.

To determine cardiovascular risk factors (diabetes, hypertension, high cholesterol, and smoking) during middle age, the researchers looked at participants’ old medical records. The records contained detailed information on self-reported demographics, lifestyle, and medical history (including medical conditions, medication use, and smoking history), as well as data on height and weight, cholesterol, blood pressure, and blood sugar levels.

To see which members went on to develop dementia over the subsequent thirty years or so, the researchers collected electronic reports of clinical diagnoses for a nine year period starting in 1994 (when electronic reporting first became available for all HMO members).

The Findings

At midlife (1964-1973), 11% of participants had diabetes, 32% had high cholesterol, 60% had ever smoked, and 19% had hypertension. From 1994 to 2003, 721 participants (8.2%) were diagnosed with dementia, with an average age at diagnosis of 74.5.

Each of the mid-life risk factors was associated with a higher risk of dementia later in life, even after researchers controlled for age, education level, race, and sex. For each CVD risk factor, the likelihood of dementia increased as follows:

  • Diabetes: 46%
  • High cholesterol: 42%
  • Smoking: 26%
  • Hypertension: 24%

Analyzed together, participants who had any one of these risk factors were 27% more likely to develop dementia; those who had any two were 70% more likely; and those who had any three, or all four, were more than twice as likely to develop dementia.

How Does This Affect You?

This study suggests that those at risk for heart disease at middle age are also at increased risk for dementia. Therefore, preventing or treating cardiovascular risk factors early could potentially lower the incidence of dementia later on. The study’s large size, long duration, and diverse population add to the credibility of these findings.

One limitation of the study, though, immediately suggests the need for more research in this area. Since the electronic reports the researchers used did not differentiate between types of dementia, they were unable to compare the increase in risk between Alzheimer’s and vascular dementia, an important distinction with regards to cardiovascular risk. Also, the unknown number of participants with dementia who died prior to 1994 could not have been included in analysis.

The exact mechanism by which CVD risk may influence cognitive decline, particularly in Alzheimer’s disease, is not well understood. The connection, however, should not be surprising. Even without showing symptoms of CVD yet, many high-risk individuals already have compromised blood flow, and thus compromised oxygen delivery to the brain. Over a long period of time, even in the absence of strokes, this low level of oxygen is bound to exacerbate the underlying disease process leading to dementia.