Researchers have identified several risk factors that affect the likelihood of developing one or more kinds of dementia. Some of these factors are modifiable, while others are not.
Age. The risk of Alzheimer's disease, vascular dementia, and several other dementias goes up significantly with advancing age.
Genetics/family history. Researchers have discovered a number of genes that increase the risk of developing Alzheimer's disease. Although people with a family history of Alzheimer's disease are generally considered to be at a heightened risk of developing the disease themselves, many people who have relatives with Alzheimer's disease never develop the disease, and many without a family history of the disease do get it.
In most cases, it is impossible to predict a specific person's risk of the disorder based on family history alone. Some families with Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, or fatal familial insomnia have mutations in the prion protein gene, although these disorders can also occur in people without the gene mutation. Individuals with these mutations are at significantly higher risk of developing these forms of dementia.
Abnormal genes are also clearly implicated as risk factors in Huntington's disease, FTDP-17, and several other kinds of dementia.
Many people with Down's syndrome show neurological and behavioral signs of Alzheimer's disease by the time they reach middle age.
Smoking and alcohol use. Several recent studies have found that smoking significantly increases 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.
Studies also 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.
Atherosclerosis. Atherosclerosis is the buildup of plaque – deposits of fatty substances, cholesterol, and other matter – in the inner lining of an artery.
Atherosclerosis is a significant risk factor for vascular dementia, because it interferes with the delivery of blood to the brain and can lead to stroke. Studies have also found a possible link between atherosclerosis and Alzheimer's disease.
Cholesterol. High levels of low-density lipoprotein (LDL), the so-called "bad" form of cholesterol, appear to significantly increase a person's risk of developing vascular dementia. Some research has also linked high cholesterol to an increased risk of Alzheimer's disease.
Plasma homocysteine. Research has shown that a higher-than-average blood level of homocysteine, a type of amino acid, is a strong risk factor for the development of Alzheimer's disease and vascular dementia.
Diabetes. Diabetes is a risk factor for both Alzheimer's disease and vascular dementia. It is also a known risk factor for atherosclerosis and stroke, both of which contribute to vascular dementia.
Mild cognitive impairment. While not all people with mild cognitive impairment develop dementia, people with this condition do have a significantly increased risk of dementia compared to the rest of the population. One study found that approximately 40 percent of people over age 65 who were diagnosed with mild cognitive impairment developed dementia within three years.