Question: My mother has Alzheimer's disease. Does that mean I will get it?
Answer: Let's start with some basic numbers. Excellent data from Canada indicates that eight per cent of people over the age of 65 will be diagnosed with dementia, and about two-thirds of those will have Alzheimer's disease. The risk of developing Alzheimer's disease doubles for every five years of life beyond age 65, making older age one of the most significant and predictable risk factors.
Familial Alzheimer's disease
In terms of risk for family members, it is important to know that there are two types of Alzheimer's disease. A very rare form of the illness, referred to as "Familial Alzheimer's disease" occurs in only about two per cent of individuals with the illness, and has been linked with three genetic mutations involving chromosomes 21, 1 and 14.
In this form of the illness, there is a 50 per cent chance of developing the disease if you have a parent with the illness who has a confirmed genetic mutation. The other disturbing aspect of this illness is that -- unlike the more common form of Alzheimer's disease that typically begin in a person's 70s and 80s -- this form of the illness can begin as early as in a person's 40s and 50s. Genetic testing is available for this, and I will discuss the topic of genetic testing in a future blog.
Sporadic Alzheimer's disease
Most people who develop Alzheimer's disease have what is called "Sporadic Alzheimer's disease," to distinguish it from Familial Alzheimer's Disease. But even with this form of the disease, genetics appear to play a role.
If you have a first-degree relative with Alzheimer's disease (e.g. mother, father, sibling), your risk of developing the illness is about two to three times higher than someone else your age who doesn't have a family member with the illness. If you have two first-degree relatives with Alzheimer's disease, your risk is probably closer to five to six times higher. While families often worry and focus on these risks, I try to get them to consider the other risk factors for the disease. After all, there is very little we can do about our genetic make-up!
Besides aging and genetics, numerous other Alzheimer's risk factors have been proposed, though admittedly, many of these are not supported by similar kinds of excellent, consistent data. Better educational attainment and lifelong participation in mentally stimulating work and leisure activities appears to be protective. Head injuries likely increase the risk. Physical exercise may decrease the risk of developing dementia, and possibly slow the decline of the illness once diagnosed.
A Mediterranean-type diet (low in saturated fats and red meats, more fish, vegetables and nuts, legumes and olive oil) appears to be protective. Mid-life vascular risk factors such as smoking, obesity, high blood pressure, high cholesterol and blood sugar, all increase the risk of developing Alzheimer's disease and other forms of dementia.
As you will appreciate -- unlike aging and genetics -- many of these risk factors are potentially under our control. In future blogs, I will explain how these can be the basis for living a brain-healthy lifestyle to reduce the risk of developing Alzheimer's disease and other dementias.
For 25 years, Dr. Nathan Herrmann has been a memory disorders specialist. He has done research in the fields of mental health in the aging, including dementia, Alzheimer's disease, depression, and suicide. Read his blog series: The Memory Doctor.
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