What do all these terms even mean? Every other day, it seems there are media reports associating Alzheimer’s with some seemingly harmless, daily activity. Can risk factors be controlled? Why are they so often numerical, like how can what I eat make me “50 percent less likely” to have a disease? Does an unhealthy diet, or decades of bad habits, cause Alzheimer’s, or not?
Saying something is a “cause” requires a case-control study. To show smoking causes lung cancer, for instance, scientists isolated lung-cancer sufferers (the case) from people with other deadly illnesses (the control) and found out how many people in each group smoked. The numbers were so overwhelming, such a high percentage of lung cancer patients smoked compared to the control group, that experts agreed smoking could be considered a cause of lung cancer.
Yet you could still argue we don’t know the cause, because some people who smoke don’t get lung cancer. Determining causes is rarely definitive, which is why we have “risk factors.”
In the above example, scientists showed causation between an act, smoking, and a disease, lung cancer. There is no such act that leads to Alzheimer’s. Instead, the disease grows out of multiple risk factors including genetics, lifestyle habits, and the environment.
Think of “risk factors” as a higher percentage. If two people are the same, except one of them has a family history of dementia, then that person has a higher percentage likelihood of getting the disease. If two people are the same, except one of them has had concussions, then that person has a higher percentage likelihood of developing Alzheimer’s. Genetics and head injuries are risk factors, because risk factors increase the potential for dementia.
“Linked to” or “associated with” is similar to saying something is a risk factor, except it’s much weaker (and often meaningless). Another difference is that these terms can imply positive associations.
Think of it as hedging. For example: Recent findings in a study led by the Boston University School of Medicine showed that regular consumption of artificial sweeteners in diet soda increases a person’s risk of Alzheimer’s. Other sources have disputed this, and even the authors of the study said their results “only show a trend among one group of people.” So no one would call being a diet soda drinker a “risk factor” for developing dementia. That language would be too strong. But articles can (and do) say consumption of artificial sweeteners has been “linked to” an “increased risk of” dementia.
“Linked to” is also different because it can be positive. A healthy diet has been “linked to” decreased risk of dementia: The Mayo Clinic has said the right diet can cut a person’s risk of dementia by 53 percent. Which brings us to the percentages.
You hear all the time that something increases or decreases risk by a certain percentage. Eating healthy lowers your odds for dementia by 53 percent. … Every five years after 65, the chances of developing Alzheimer’s doubles. … Someone with diabetes is 65 percent likelier to get Alzheimer’s. … These numbers need context, because (on the negative end) they’re not as scary as they seem.
Think of yourself as one in a group of 100 people. Ten percent of the population, on average, develops Alzheimer’s between 65 and 75, so 10 out of the 100 will get it. How likely you are to be among those 10 is where the percentage increases and decreases come in. If you eat healthy, there are about 50 people who are more likely to be among the 10 than you.
If you have diabetes, you move closer to the 10, but if someone with diabetes is 65 percent likelier to get Alzheimer’s, that doesn’t mean 65 out of 100 people with diabetes gets Alzheimer’s, it means that within the group of 100, those with diabetes are 65 percent more likely than those without diabetes to be among the 10 with Alzheimer’s. It provides a relative understanding of where you are, compared with everyone else. But of course even that can’t be exact, because other factors like diet skew the percentage.
An epidemiologist (a scientist studying diseases in populations) would say that calculating risk is complicated and error-prone. Use these numbers as basic guidelines, and focus on risk factors you can control.
Being over 65 is a risk factor, and every five years the risk of developing Alzheimer’s doubles. (About 10 percent of people between ages 65 and 75 have Alzheimer’s, but more than 40 percent have developed it by 85.) Age, obviously, is something we cannot control. We also can’t control family history or genetics, and though family history is not as closely tied to increased rates of Alzheimer’s as to other less-common kinds of dementia (like young-onset Alzheimer’s and Huntington’s disease) experts advise that someone with a familial history of the disease is at slightly higher percentage risk because of genetics.
Smoking has been linked to – or shown to increase – the risk of Alzheimer’s, because it can decrease the circulation of blood to the brain. Bad fitness – not exercising enough – is also a risk factor for the same reason. Maintaining a healthy cardiovascular system decreases the risk of Alzheimer’s, and your personal actions (Stop smoking, and go outside and sweat!) increase or decrease the risk or likelihood of developing the disease. The percentage increase or decrease in likelihood is small, but, again, each of us is one in a population that may as well be a control group (without the snooping scientists).
Head injuries have been linked to developing dementia later in life, because an impact on the brain can cause plaques to form, so protect your head by wearing a helmet when it’s appropriate, like while bike riding, and buckle your car seat belt every time.
Bad diet is an increased risk factor, so you increase your odds of avoiding dementia by eating brain foods including leafy greens and other colorful vegetables, nuts, berries, beans, whole grains, fish, chicken and olive oil.