The best predictor of risk for developing Alzheimer's disease (AD) is advancing age. Approximately 1% of individuals aged 60 years old have AD, while 3% between 65 and 74 have the disease, and by age 85 at least 40% have AD.

Women are 1.2 to 1.5 times more likely than men to suffer Alzheimer's disease. Some have wondered whether this is because women live longer. However, this increased risk holds up even when women's longer lives are taken into consideration.

A family history of AD is a general risk factor for development of AD in later generations. A particular gene, the apolipoprotein E (APOE) gene, has three alleles (different forms of the gene). These three alleles are epsilon 2 (ε2), epsilon 3 (ε3) and epsilon 4 (ε4). The ε3 allele is the most common gene inherited, ε2 and ε4 being inherited less often. The APOE gene story is interesting. We inherit one gene from each parent and the inherited gene will be one of the three alleles. So there are six possible inherited combinations: ε2/ε2, ε2/ε3, ε2/ε4, ε3/ε3, ε3/ε4 and ε4/ε4. Inheriting APOE ε4 alleles increase the risk of developing AD. The presence of at least one APOE ε4 gene increases risk from approximately 9% to approximately 29%. People with two ε4 alleles are at even greater risk of developing AD, perhaps with an earlier age of onset. There are considerable racial and ethnic differences in distribution of these pairs with 2-3% of the population inheriting the ε4/ε4 pairing. Importantly, some people with two ε4 alleles never get the disease and others who do develop AD do not have any ε4 alleles.

It is possible to identify which form of the APOE gene a person has inherited. However, the detection of the ε4 genetic characteristic is not presently sensitive or specific enough to be helpful in predicting who will or will not develop Alzheimer's disease. Interestingly, presence of ε2 and ε3 alleles may reduce the risk of AD by allowing natural brain processes to remove beta-amyloid (a component of plaques - see what causes Alzheimer's disease) from the brain more effectively than the ε4 allele.

Family history of other dementias, less formal education and low occupational status and income (which may be associated with less education) are associated with greater risk of developing Alzheimer's disease. Also associated with greater risk are head injury, low levels of vitamin B12 and folate and high levels of homocysteine (a blood protein). Risk for Alzheimer's disease may be lower in those who eat more fish and foods high in antioxidants, eat less red meat and consume wine daily in low or moderate amounts, but this has not been established definitively.

back to top