There are several risk factors that affect the likelihood of developing one or more kinds of dementia. Some are modifiable (such as smoking), while others are not (such as family genetics).

But first, a caveat: When thinking about risk factors for dementia, it’s important to understand a key distinction. Correlation and causation is not the same thing. For example, having diabetes is a risk factor for both Alzheimer’s disease (AD) and vascular dementia. That does not mean that diabetes “causes” AD or vascular dementia; and indeed, not all people with diabetes develop dementia. Baring this important distinction in mind, risk factors associated with developing dementias include the following:

Age

The risk of developing Alzheimer’s disease, vascular dementia, and several other dementias increases significantly with advancing age. For example, in the U.S. nearly half of people 85 years of age and older are believed to have Alzheimer’s disease.

Genetics/Family History

Many forms of dementia seem to have a genetic component—it often runs in families. In addition, certain mutations in some specific genes have been identified as increasing risk for developing dementia.

Atherosclerosis

From the Greek words athero (meaning “gruel” or “paste”) and sclerosis (meaning “hardness”), atherosclerosis is the thickening and hardening of the artery walls due to plaque build-up. Plaque is comprised of cholesterol, fat, calcium and other substances in the blood. This build-up can narrow the arteries to the point where it interferes with the delivery of oxygen-rich blood to the brain—which impairs the ability of the affected neurons (brain cells) to function properly. This series of events, in turn, leads to the death of those neurons and their associated neuron-to-neuron connections.

Smoking

Several recent studies have found that smoking may significantly increase the risk of mental decline and dementia. People who smoke have a higher risk of atherosclerosis and other types of vascular disease – which may be the underlying causes for the increased dementia risk.

Alcohol Use

Studies have found that drinking large amounts of alcohol appears to increase the risk of dementia. However, other studies have suggested that people who drink moderately have a lower risk of dementia than either those who drink heavily or those who completely abstain from drinking. 

Cholesterol

Having high levels of low-density lipoprotein (LDL)—the so-called “bad cholesterol”—appears to significantly increase a person's risk of developing vascular dementia. This may be due, in part, to the association between atherosclerosis and high cholesterol.

Homocysteine

A building block of protein, called homocysteine (an amino acid) naturally circulates in the blood. However, recent studies suggest that having higher than average blood levels of homocysteine is a risk factor for a number of neurodegenerative diseases, including Alzheimer's disease, vascular dementia, cognitive impairment, and stroke.

Diabetes Mellitus

Recent studies suggest that having diabetes may be associated with an increased risk of developing both Alzheimer’s disease and vascular dementia. Diabetes mellitus is also a known risk factor for atherosclerosis and stroke, both of which contribute to vascular dementia.

Psychological and Experiential Factors

There is mounting research suggesting that psychological and experiential factors may be a risk factor for dementia. For example, studies have found that social isolation and not regularly participating in cognitively stimulating activities may be associated with an increased risk of developing Alzheimer’s disease.

Mild Cognitive Impairment (MCI)

MCI is a clinical condition in which: 1) a person experiences memory loss greater than expected for their age, 2) the memory deficit is enough to be noticed and measured, and 3) the deficit is not enough to compromise a person’s independence, i.e., they can still take care of themselves and conduct their normal activities. About 40 percent of people with MCI develop Alzheimer’s disease (AD) within three years—which means people with MCI may or may not progress to AD.

Down Syndrome

Studies have found that by their mid 40s, it’s not unusual for people with Down syndrome to develop the hallmarks of Alzheimer’s disease and the associated onset of neurodegeneration, loss of brain cells, loss of neuron-to-neuron connection, and dementia.