Yesterday, we looked at three factors that researchers have found to correlate with dementia: poor oral health, hearing loss, and vision loss. But there are others.

A study sponsored by the University of Exeter, published last February in the Journal of the American Medical Association – Neurology followed over 350,000 people in the U.K. (Britain) who were younger than 65 — correlated with lifestyle factors — to see which ones would develop young-onset dementia (YOD).

The researchers found 15 such factors. Their main conclusion was that “a wide range of risk factors were associated with YOD, and targeted interventions may prove effective for dementia prevention in middle-aged adults… ”

Here are the ones that were “robustly associated” with YOD:

We investigated the association of 39 risk factors with the incidence of YOD. We identified 15 factors robustly associated with YOD. Higher formal education, lower physical frailty (handgrip strength), and alcohol use (relative to abstinence) were associated with lower incidence of YOD, whereas having 2 APOE ε4 alleles, lower socioeconomic status, high CRP levels, orthostatic hypotension, stroke, diabetes, heart disease, depression, hearing impairment, vitamin D deficiency, alcohol use disorder, and social isolation were associated with an increased risk. The paper is open access.

Correlation? Causation?

Evidence is assessed in studies like this based on correlation. We need to keep in mind the oft-cited difference between causation and correlation.

Causation means that we can show a direct causal link. Suppose, for example, that researchers can demonstrate conclusively that a specific aspect of poor oral health causes a specific dementia symptom. That’s causation. But that level of evidence is rarely available because both poor oral health and dementia are complex and how they affect different individuals may vary widely.

Correlation just means that two things are found together more often than chance would lead us to expect. It is a much less certain form of evidence. But that does not mean that it should be ignored. If, for example, seniors with poor oral health are significantly more likely to be diagnosed with symptoms of dementia than others are, it would be unwise to ignore the loud signal — even if we cannot show definitive cause and effect for each case.

Most of the time, most of us settle for correlation. For example, if living in town A correlates with a greater likelihood of finding work than living in town B does, most people who need to work will choose Town A. Researchers may come up with useful findings about why exactly that is so and what might change it. Some researchers may even claim that the employment difference is merely a statistical artifact. But that’s for experts. Most of the time, most of us are safe enough with a reasonable correlation.

Some significant risk factors

In that spirit, here are some of the factors that the researchers found to be significantly associated with early dementia (YOD):

● Heredity played some role. Having two of the ApoE4 ε4 gene variants was linked to a higher risk of YOD.

But lifestyle factors played a big role too, especially these three:

● Vitamin D deficiency: “We found both vitamin D deficiency and high CRP levels were associated with increased risk of YOD. It has been suggested that vitamin D acts as a neurosteroid that protects against neurodegenerative processes. Notably, CRP was only significantly associated with YOD when vitamin D was included in the model.”

CRP is C-reactive protein, which rises with inflammation. But the more significant factor here, vitamin D — which is essential for bone health — can largely be got from sunlight.

It’s worth asking whether Vitamin D deficiency may be related in many cases to not getting outside much. If so, that likely promotes a second factor in YOD…

● Social isolation: “For social isolation, participants who visited friends or family once a month or less had a higher association with YOD than persons visiting friends or family more often.”

Rarely interacting with others may correlate with the onset of dementia but may also promote it, in the same way that vision and hearing loss could do. When there is little outside input, we might expect the mind to suffer.

● Alcohol use disorder (alcoholism): “Our results showed alcohol use disorder is associated with higher risk of YOD, which aligns with results from previous studies, although in our sensitivity analysis investigating reverse causation, the association ceased to be significant, indicating that impeding YOD might also cause alcohol use disorder due to excessive drinking. Our findings regarding heavy alcohol use are complex and should be interpreted with caution.”

As we can see, this is a more complex issue…

Why is alcohol use a “more complex” issue?

Clearly, the relationship between alcohol use and YOD is not a simple, graduated one. That is often the way with correlation, as opposed to causation. The researchers offer a suggestion: “For moderate alcohol use, this may be due to the healthy drinker effect, in which people who drink are healthier, while abstainers are more likely to not consume alcohol because of poor health or use of medication.”

Or, one might add, if a person’s cognitive issues have already come to the attention of others, that person may not be left alone near alcohol any more, regardless of personal intentions. One thing stands out though; heavy alcohol use is not associated with any cognitive health benefit.

Something else we don’t know for sure

We can’t know in any given case whether avoiding risk factors prevents dementia or simply puts it off. But how much that even matters depends on individual longevity. Delaying the onset of dementia until, say 85, means that it never happens to a person who only lives to be 83.

In health matters, correlations can provide valuable information but they need to be assessed carefully if we want to ferret out the true, often complex relationships.

You may also wish to read: Fallout from Alzheimer research failures: Does anything work? Other research suggests that treating poor oral health, vision loss, and hearing loss might delay or reduce the effects of cognitive decline. Perhaps, instead of seeking a single cause-effect pattern, we should look at overall cognitive decline and health neglect. Many elements are treatable.