Alzheimer's Risk Factors

What Causes Alzheimer's Disease and Who Gets It
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Quick summary

Short-term memory loss is one of the most noticeable signs of Alzheimer's disease. But the disease process usually begins before symptoms are noticed. To assess someone's risk of becoming one of the more than 5 million Americans with Alzheimer's, it's helpful to understand the risk factors that increase the odds of developing the condition.

What is Alzheimer's, and who's at risk?

Although certain basic lifestyle changes can help delay the onset of the disease in some people, the exact cause of Alzheimer's disease isn't yet understood. Alzheimer's is a progressive neurodegenerative brain disorder: Normal brain cell function is gradually destroyed, leading to irreversible declines in memory, cognition, and behavior. But what causes things to go awry remains unknown. It may be that Alzheimer's has several causes or that the interplay between genetic makeup and certain risk factors determines who's affected.

The following questions are based on the known risk factors for Alzheimer's. See how many apply to your family (or to you, to assess your risk of eventually developing the disease).

1. How old is he or she?

  • At lower risk: Under age 70
  • At higher risk: Over age 85

Why age matters: Age is the most significant established risk factor for Alzheimer's disease. One in 7 people over age 71 has some form of dementia, and 2.4 million of these have Alzheimer's, according to the latest National Institutes of Health data. The percentage of people with Alzheimer's rises from just 2.3 percent of those ages 71 to 79 to 18 percent of those ages 80 to 89, and 29.7 percent of those 90 or older. Some estimates say as many as half of all people over age 85 have Alzheimer's disease.

The total number of people with the disease doubles with every five-year age jump after age 65.

2. Is it a he or a she?

  • At lower risk: Men
  • At higher risk: Women

Why gender matters: Because women live longer than men, on average, and Alzheimer's disease risk rises with age, more women than men develop it. In addition, some research indicates that a lack of estrogen after menopause may contribute to the fact that, overall, slightly more women are affected. Taking hormone-replacement therapy has not been shown to protect against Alzheimer's.

Vascular dementia is more common in men than women, probably because more men develop contributing factors such as hypertension and vascular problems.

3. Have any of his or her parents or siblings had Alzheimer's?

  • At lower risk: No family history or known genetic predisposition
  • At higher risk: A family history or known genetic predisposition

Why family history matters: People with a family history of Alzheimer's are more likely to develop the disease. The risk is thought to rise with each relative who had it.

It's unknown, though, exactly how much of this association is due to genetic factors and how much is due to shared lifestyle factors. Most experts believe that some combination of the two is responsible. Even when an immediate family member has the disease, however, your increased risk is only slightly higher than if your family had no history of dementia.

Up to 80 percent of Alzheimer's risk may have a genetic component, according to a 2006 study of more than 12,000 Swedish twin sets -- a greater influence than was previously thought. But having a relative with the disease does not doom a person to a similar fate; even among identical twins, when one male twin had it, almost half of the time the other twin did not. (Among female twins, the other twin developed Alzheimer's 60 percent of the time, a difference researchers attributed to the fact that women generally live longer than men.) If Alzheimer's were solely genetic, both twins would have developed the disease, and at about the same time.

So far, only two types of genetic tests for Alzheimer's exist, and neither of these blood tests is currently recommended for routine use.

  • One kind of genetic test identifies a person's risk of developing Alzheimer's disease but doesn't guarantee whether or not he'll develop the condition. Everyone inherits a form of the apolipoprotein (APOE) gene from each parent. Apolipoprotein helps carry cholesterol in the blood. Its three most common forms are APOE-e2, APOE-e3, and APOE-e4. Those who have two copies of APOE-e4 seem to be at the highest risk of getting Alzheimer's and of developing symptoms earlier in life. Having one copy of APOE-e4 also elevates the risk. Only about 15 percent of people carry the APOE-e4 form.

It's thought that APOE is only one of many genes involved in the disease process. For instance, while it's considered a strong risk factor, the APOE-e4 gene shows up in only about 40 percent of all people with Alzheimer's disease. Identifying other genes that may be involved is a focus of ongoing research. The National Institute on Aging is conducting an Alzheimer's Disease Genetics Study, which is currently recruiting sibling pairs. These pairs must both have developed Alzheimer's after age 60 and must have a third family member with or without the disease who's willing to undergo cognitive tests and blood sampling.

  • A second type of existing genetic test for Alzheimer's disease can predict with certainty who develops one rare form of the disease. This is early-onset familial Alzheimer's disease, which strikes between the ages of 30 and 65 and stretches through multiple generations. It accounts for less than 5 percent of all cases.

Does he or she smoke?

  • At lower risk: Nonsmokers, former smokers
  • At higher risk: Current smokers

Why smoking matters: Evidence is growing that smoking raises the risk of developing Alzheimer's disease by as much as 50 percent. In late 2007, Dutch researchers who tracked almost 7,000 people age 55 or older for 7 years reported that current smokers were more likely to develop dementia than people who had never smoked or had quit. Interestingly, the effect was more pronounced for people who did not have the APOE-e4 gene (the type known to be most vulnerable to the disease). Smoking didn't raise the already elevated risk of Alzheimer's in those who had the APOE-e4 gene.

It's thought that smoking damages the cardiovascular system and causes oxidative stress, both conditions that are associated with Alzheimer's.

You may have heard that smoking protects against dementia -- which is a myth. This persistent idea grew out of flawed studies and because fewer people with Alzheimer's were smokers. But in fact smokers, tend to have shorter life spans and are less likely to live to the advanced ages at which Alzheimer's most often strikes.

5. Does he or she have diabetes?

  • At lower risk: No history of diabetes
  • At higher risk: Those with type 2 diabetes

Why diabetes matters: People with type 2 diabetes have at least double the risk of developing Alzheimer's compared with people without diabetes. The risk was 65 percent higher for diabetics in 2006 data from the ongoing Religious Orders Study of priests and nuns. Some studies have found that the higher the blood sugar levels, the higher the dementia risk.

The mechanics behind the Alzheimer's-diabetes link aren't certain, but this is an area of intensive research. The leading explanations:

  • High blood sugar may cause vascular problems. It's known that diabetes can cause cardiovascular problems and strokes; reduced blood flow to the brain may cause small-vessel damage there that leads to vascular dementia (a type of dementia that can appear with Alzheimer's).

  • Insulin resistance leads to inflammation that can damage the brain. Insulin resistance occurs in diabetics when their cells can't use insulin properly to move glucose from the blood to be used for cell energy. The pancreas then makes extra insulin to compensate, which builds up in the blood and creates inflammation, which damages brain cells.

  • Insulin resistance in the brain disrupts the proper formation of neuron connections. The autopsied brains of people with Alzheimer's always show amyloid plaques, clumps of the protein beta amyloid, which ruin brain cell connections. It's been discovered that this substance destroys the brain cells' receptors for insulin, which is used by the brain to make new memories. This results in dementia and memory loss.

As evidence of a clear biochemical link between the two conditions grows more compelling, some are calling Alzheimer's disease "type 3 diabetes."

There's also a likely genetic link between diabetes and Alzheimer's. People with diabetes who also have the APOE-e4 gene (the type that places a carrier at highest risk for Alzheimer's) were two-and-a-half times more likely to develop the disease, according to a 2008 National Institute on Aging study.

6. Does he or she have a history of being overweight?

  • At lower risk: Low BMI in midlife
  • At higher risk: Overweight or obese in midlife

Why weight matters: Being overweight or obese as measured by body mass index is well associated with an increased risk of developing dementia. Men with the leanest body mass index (BMI) in their late 40s and mid-50s were the least likely to develop Alzheimer's in a 20-year study of more than 7,000 Swedes; those who were heaviest were most likely. This same study also later found that women who were overweight at 70 were more likely to develop Alzheimer's in the next 10 to 18 years.

People who are overweight are more likely to have related health problems that are also linked to Alzheimer's, such as hypertension, high blood pressure, cardiovascular disease, and diabetes.

A related risk factor is if someone was previously overweight but has had unexplained weight loss recently. Weight loss associated with dementia may begin six to ten years before other symptoms become obvious. Research isn't clear whether this is because of declining ability to prepare meals or is a function of the disease process.

What Causes Alzheimer's Disease and Who Gets It

At lower risk: No injury At higher risk: Prior head injury, especially after age 50

Why head injury matters: Prior head injury -- even years earlier -- is linked with a greater risk of developing Alzheimer's, though it's not clear why. That's not to say that any youthful bump will lead to Alzheimer's. The injury itself isn't thought to directly cause the disease, although it may hasten the process. But the more severe the trauma, the greater the risk of developing Alzheimer's, according to a large study of World War II veterans. The most concerning are thought to be falls with head injuries that occur later in life.

8. Was he or she a college graduate?

  • At lower risk: Higher education level
  • At higher risk: Lower education level

Why education matters: People with lower education levels are more often affected by Alzheimer's disease. Researchers theorize that longer education helps the brain develop stronger, denser, more complex connections between brain cells, creating more cognitive reserve. This positions the brain to be better able to withstand the abnormal stresses associated with Alzheimer's disease and compensate for the changes that occur.

9. Does he or she consume a balanced, low-fat, vitamin-rich diet?

  • At lower risk: Heart-healthy diet rich in antioxidants
  • At higher risk: Eating high-fat foods and an unbalanced diet

Why diet matters: Although there's no "Alzheimer's-prevention diet," a growing body of research indicates that nutrition influences brain health and may protect against or postpone cognitive decline. Specifically, your overall risk of Alzheimer's may be lower if you consume:

  • B vitamins: People who are folate (B-9) deficient may run triple the risk of developing dementia, according to recent South Korean data. Previous research showed vitamin B-12 to be protective.

  • Vitamin E: Those who consume the highest dietary amounts of this antioxidant have a lower incidence of Alzheimer's. Vitamin E supplements have not been shown to have the same protective effect.

  • Vitamin C: Another antioxidant, vitamin C, seems to have a protective effect in certain people, though possibly only in dietary form. Antioxidants counter the effects of oxidative stress, which is linked to nerve cell damage and death. Over-the-counter vitamin C supplements did not reduce Alzheimer's risk in a recent study of 2,969 people 65 and older.

  • A heart-healthy diet: People who consume a generally balanced diet that avoids too much fat and includes complex carbohydrates are less likely to develop conditions that are Alzheimer's risks, including obesity, diabetes, and cardiovascular disease.

10. Does he or she exercise regularly?

  • At lower risk: Active lifestyle
  • At higher risk: Sedentary lifestyle

Why exercise matters: Regular exercise reduced the risk of dementia by as much as 40 percent in a 2006 study of nearly 2,000 people age 65 and older. This was the first study to factor in one's pre-existing physical condition. And those most frail at the start of the study showed the greatest protection against dementia if they exercised. The threshold that made a difference: physical activity for at least 15 minutes, three times a week. Exercise both lowers the risk of obesity and cardiovascular conditions linked to Alzheimer's and reduces the risk of developing dementia.

Previous research has shown that the variety of activity engaged in is more important than the intensity of a workout, when it comes to providing brain benefits. (Variety of workouts had no benefit, though, to those with the APOE-e4 gene variation most commonly associated with Alzheimer's.)

11. Does he or she engage in mentally stimulating activities?

  • At lower risk: Varied, frequent "brain workouts"
  • At higher risk: Lack of mental stimulation

Why mental stimulation matters: Just as physical activity exercises the body, "cognitive activity" exercises the brain. Numerous studies now support the "use it or lose it" idea that mental workouts lower the risk of dementia. For example, participants in the Religious Orders study who attended museums, worked puzzles, and read newspapers were 47 percent less likely to develop Alzheimer's after four years than those who did such activities less frequently.

Brain-stretching activities can't prevent Alzheimer's, but they help the brain better withstand the physical changes associated with it. What's key: The stimulation should be ongoing.

12. Is he or she socially stimulated?

  • At lower risk: Social engagement
  • At higher risk: Social isolation and loneliness

Why social stimulation matters: Isolation is a risk factor for developing dementia, probably because there's less opportunity for mental stimulation. But a surprising 2007 study also found that people who were around others but felt lonely (emotional isolation) were also at higher risk for Alzheimer's. This sense of loneliness wasn't a result of the disease (as is often the case with depression) but a clear precursor.

Paula Spencer Scott

Paula Spencer Scott is the author of Surviving Alzheimer's: Practical Tips and Soul-Saving Wisdom for Caregivers and much of the Alzheimer's and caregiving content on Caring. See full bio

about 3 years, said...

Reassured me that I am low risk despite being 87.

about 3 years, said... gives very varied read-ups on many medical conditions reg. which most of us wory sometime or other ; Paula Scots' regular notes FOR FREE help very much to take therapeutic steps / be worry free . Thanx Paula and hope u aply al to self to remain hapy and healthy till 125 ---- usb National Awardee from India

about 3 years, said...

Straight forward understandable and detailed information supported by research. Thank you.

over 3 years, said...

want more info emailed to me

over 3 years, said...

Thank you...will formed and easy to understand.

over 3 years, said...

I am sharing my experiences as my wife having DEMENTIA since 2008, i am her caretaker, morning to night for toilet, bath, feeding, exercise with " Morning Walker", oil massaging on both the leg, medication etc. She can'nt talk, neither stand/ walk, using Wheel chair. Her main food is Cow milk, cornflakes, Oats, Pulses & wheat bread ( Roti ).I am 66 & she is 59. I am first stage diabetic, well in control with medication & using Neurobion tab twice in a day to keep myself healthy & fit. please advise me , how tokeep myself healthy & protective from Dementia.

over 3 years, said...

All four pages that I read revealed lots of information about Alzheimer's. My great aunt had diabetes.She was overweight, and had high blood pressure. She lived to be 99 years old ,even after having part of her leg amputated. Her memory was intact during her whole lifetime. She was involved in her church, and had a beautiful singing voice. I found her quite amazing.

over 3 years, said...

I am so frustrated, my mom seems so unlike herself, she is suspicious of everything I do yet is letting a guy I used to date stay here and keeps giving him money, even though I am not with him nor do I get along with him. He has been here 4 mo and hasn't paid a dime, she says she likes his company yet he terrorists me about how easy he can get me kicked out, thrown in jail, etc. he has even threatened to hit me in front of her and she takes his side. What is that?

over 3 years, said...

Great article, well written and informative. Explains alot of things

over 3 years, said...

An excellent article

over 3 years, said...

I live in Canada and, since most of the information pertaining to care facilities seems to relate to USA localities ( irrelevant to me), had decided to unsubscribe from your site. When I investigated a few more of your pages and articles regarding the effects of the disease on both patient and caregiver(s), I reversed my decision. I found some very helpful information. Thank you so much.

almost 4 years, said...

Interesting that all the caregivers note that skinny intellectual women are what are prevalent in the nursing homes. Maybe this has to do with financial means and not a good indicator. I think the tips are good tips for anyone for any disease, but clearly no one knows how you get it.

almost 4 years, said...

The most helpful part is knowing that we dont' really know the why? We have to ask family members' on both sides' to see if this has happened with another loved one and just how it came about. "Yes" there are meds' out there that help, however not all meds' work for each person.

almost 4 years, said...

I am in good physical condition, am active with wood sculpturing, and water color painting. Short term memory is significant, ( from table to sink).

almost 4 years, said...

pls more info pleas

almost 4 years, said...

my mother had Dementia I was unhappy but understood why she did not want to come live with me. I am Scottish Highlander, my mother was very independent. I used to travel to Scotland to be with her for a wee while.. When she was herself she was the funniest person and loved all children and animals. Mother was always worried and could not understand why she lived alone. I wanted so much to take her with me but she would not give in. To her she was a Highlander, she was a very proud person and independent Highland independent that is what she would say. My mother was lost , mammy all her life was a very busy person. Now she was lost everyone had their life and it did not include her, but she did not want to be a burden to any of her family.I tried to tell her that it was my turn to take care of her but she would not come with me. I wonder if when a person is busy and always the brain is working fast all those years and now now nothing. Many time she thought I was the mother and she the child, I would sing songs to her and we would dance. When it was time to leave it broke my heart. We had this very close connection and when I got the call to come home fast I knew she was dying, I missed her by 1 hour. I was told by my sisters that she knew everyone and could not wait any longer, said I would be late for my own funeral and sang For I am no awoe tae bide awoe Ill aye come back an see yea. I know that there is a chance I may get it . I would like please if you know of what you may do that might help by chance to prolong the chance. I write poetry, stories for children and working on my second novel which I hope will be published. I leave that for my grandchildren. Thank you

almost 4 years, said...

Alzheimer's is one of the most common form of dementia and one of the leading cause of death among Americans, sadly, the programs and organizations for Alzheimer support is also one of the least funded. A lot of people in long term care facilities are affected by this illness. I just would like to share this infographic about long term care alzheimer's dependents

almost 4 years, said...

It really don,t tell you much at all. They don,t know how it gets started. Who will get it nothing.

almost 4 years, said...

Paula, thank you for this wonderful article. You made me feel encouraged today.

about 4 years, said...

I have heard that the same chemical in the brain that keeps our thoughts organized is the same chemical that we use to move our large muscle groups. apparently Tia Chi helps a lot in preventing and lessening the symptoms of Alzheimer's Disease. There is also some concern that cloistral medication causes memory problems. There is some worry about the E.M.F. and other electricity in the air that causes problems with brain function. A Faraday cage may help.

about 4 years, said...

I work in a nursing facility. I have done this kind of work for 30+ years. I have noticed that very thin,school teacher are our main one with Alzheimers. So no this did not help

about 4 years, said...

This is a very well set out article, and I found it very helpful

about 4 years, said...

Reduced my concern (I'm 84).

about 4 years, said...

Just fascinating how many different things in our lifestyle may influence prevention from getting Dementia...

about 4 years, said...

I meant that my father's doctors had asked us to remove car keys and weapons.

about 4 years, said...

Any advice for a caregiver who faces not only aging father's memory loss daily, but relatives that are in denial of memory loss diseases happening in their family. My father's brothers and sisters and my siblings do not speak to me. They want to make all decisions after my father's complained of my husband and I taking away his car keys and weapons from my father's doctors. They feel he should drive to the store and short errands even though he has no license anymore. They feel that he should have his guns and various sharp weapons for protection. Meanwhile I am the one doing all the daily work tending to him. He no longer is able to cook, shop, rake leaves, take out the trash or do light house cleaning. I am it. Feeling rather stunnded at the family's turning against me when I am the one doing the caregiving.