Why is it so hard to figure out what diet and lifestyle factors affect Alzheimer's?

I noticed a great writeup by Michael Simpson, CEO of Skeptical Raptor, on this topic. Simpson does a great job of addressing the primary issues that come up when scientists attempt to do research in this area:

First of all, the studies rely on self-reported measures. The scientists don’t follow people around 24/7. They just ask them “how much do you smoke,” “what do you eat,” etc. The problem with this is that someone who has poor health outcomes will assume they did something wrong and focus on what it is they did wrong. They will be ungenerous about their past “I smoked too much,” “ate too much,” “slept to little,” etc. So it’s a lot of speculation. Someone with the same diet and behavior who had good health outcomes will likely react in the opposite way, speculating why they’ve done so well. In either case it does become sort of speculative and not super informative.

Secondly, the studies are correlational, meaning they don’t know what causes what. Did you stay married because you’re religious, or are you religious because you stayed married? It’s hard to know. Also, it could be a third variable that we haven’t thought about that causes both the religiosity and the commitment to marriage. It can be very hard to parse out.

Here is a quick example more closely related to nutrition: In the U.S. we’ve been told for decades that eggs are bad for us. Now we notice that healthy people eat fewer eggs. Are they healthy *because* they eat fewer eggs? Or do they eat fewer eggs because they want to be healthy and they’re generally told that’s what they need to do? Gets confusing, right?

In the case of the actual study that Simpson looks at, there are six healthy habits that can stave off mental decline. They are listed in order from the largest effect to the smallest. This may be true but consider the study limitations:

1. Healthy diet, β =0.016

2. Active cognitive activity, β=0.010

3. Regular physical exercise, β=.007

4. Active social contact, β=0.004

5. Never/former smoker, β=0.004

6. Never alcohol, β=0.002.

The good thing is that we have nothing to lose by adopting these habits since they can help in whole host of areas.

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Article is written for Neurology Associates Neuroscience Center.