What Really Causes Dementia

by Carole Jackson, Bottom Line Health

What really causes dementia? What a relief it would be to know the answer, since practically everyone I know worries about whether the occasional “senior moment” or “brain fog” is a sign that something more serious is going on. With the incidence of dementia rising worldwide, scientists are studying this issue from every possible angle, trying to learn what illnesses, lifestyle habits and environmental factors are at play — but, to be honest, as yet no one knows for sure.

Making this particular challenge even more difficult (or rewarding, I suppose, depending on your perspective) is that dementia researchers seem to find new associations with every rock they turn over. Having a big head? Exposure to bright lights? Both may be protective. Living a sedentary lifestyle, smoking and having high cholesterol at midlife? Trouble lies ahead.

What We Do Know…

Let’s take a quick trip through some of the more recent research findings so that you can see what I mean:

Healthy habits that seem to protect against dementia…

Using your brain, living a full life. A study of 951 older, dementia-free patients found that those who reported having a purpose in life at the study’s start were half as likely to have Alzheimer’s disease seven years later… while numerous studies showed that engaging in mentally stimulating activities, such as doing crossword puzzles, playing cards and attending movies and plays, holds back development of dementia.

Good nutrition — including taking tea. A four-year study of 2,258 dementia-free New Yorkers found 40% lower risk for Alzheimer’s among those who followed the Mediterranean diet (lots of fruit, vegetables, fish, olive oil, legumes and cereals and moderate alcohol intake) than for those whose diets weren’t as healthy. Studies have also found that drinking tea regularly is protective — for instance, one 14-year study found that tea drinkers were 37% less likely to develop dementia than those who don’t drink tea.

Exercise. A vast body of research finds regular exercise is protective. For instance, one study found that those who engage in active exercise, such as doing yard work or biking, had a 29% lower risk for dementia than people who got little or no exercise.

Meanwhile, signs that point to increased risk for other health problems are also associated with a higher risk for dementia…

Vitamin D deficiency. An international group that assessed cognitive decline of 858 seniors over six years found that people deficient in vitamin D were more than 60% more likely to have experienced significant cognitive decline and 31% more likely to have problems with executive function (which includes thinking, learning and memory) than those with healthy levels of vitamin D.

Cardiovascular risk factors. One large study that followed almost 10,000 people over age 40 found that even marginally high cholesterol (200 mg/dL to 239 mg/dL) at middle age increased risk for late-life dementia by about 50%, while other studies have correlated high blood pressure with dementia.

First- and secondhand smoking. Beyond the countless studies linking smoking and cognitive impairment, a six-year study of almost 5,000 nonsmoking adults by researchers from the Universities of Cambridge and Michigan found that those who reported long-term exposure (30 years or more) to secondhand tobacco smoke were about 30% more likely to develop dementia than those who reported no regular exposure.

And if you already have certain diseases, odds are higher that you’ll get dementia, too…

Diabetes. Substantial research has found diabetes is a risk factor for dementia. For example, a new study by London’s Institute of Psychiatry found that participants with diabetes were nearly three times as likely as nondiabetics to develop dementia.

Depression. Several studies find depression increases dementia risk. Of nearly 1,000 elderly participants from the 62-year Framingham Heart Study, those who were depressed when first examined had almost double the risk for dementia 17 years later.

Is There a Theme Here?

I called Peter Rabins, MD, MPH, Richman Family Professor for Alzheimer’s and Related Diseases at the Johns Hopkins University School of Medicine, to ask his opinion. He told me that it makes sense, in practical terms, to summarize risk factors for dementia as being pretty much inclusive of everything that we already know is bad for your heart. But when it comes to prevention, he added — frustratingly — the massive amount of research has so far produced “no strong evidence that we can ‘prevent’ dementia by doing anything in particular.”

A major problem is that most of the studies have some basic limitation or flaw in research design, Dr. Rabins told me. For instance, most of the existing research compares people who develop dementia with those who don’t… but new research indicates that dementia may be present decades before symptoms are noticeable enough to make a diagnosis, so it may be that some of those patients weren’t actually dementia-free. Another flaw: Healthier people tend to take better care of themselves, so it’s hard to tease out which factors or habits are responsible for cognitive health.

In the Meantime…

What scientific advice can we offer, based on what we know at this point? I asked Dr. Rabins this question. He pointed out that when it comes to preventing dementia, the odds clearly favor those who live a healthy lifestyle. For instance, since 10% to 20% of dementia in the US is known to have vascular causes, we can infer that eating a healthy diet, exercising and managing stress are beneficial. The fact that only 30% to 60% of dementia risk is thought to be genetic means that there is plenty of reason to do all you can to reduce environmental risk — another argument for health-promoting habits and choices.

The search for the cause or cure will certainly continue, but reviewing what we already do know says quite a lot. Living well and with joy seems to boost the odds that you will remain cognitively intact, whereas all those things that are bad for you… are bad for you.

Peter V. Rabins, MD, MPH, Richman Family Professor for Alzheimer’s and Related Diseases, vice-chair for academic affairs, department of psychiatry and behavioral sciences, Johns Hopkins University School of Medicine, Baltimore, and coauthor of The 36 Hour Day (The Johns Hopkins University Press).