You may have seen the headlines: “Psoriasis tied to higher Alzheimer’s disease risk.”

Great. Just another thing to worry about thanks to psoriasis, right?

But when you dig into the research, you realize it’s mostly just the usual media hype: there’s no need to panic the next time you misplace your car keys. There’s even some good news to report.

The background

Alzheimer’s disease is the most common cause of dementia. Still poorly understood, this terrible disease appears to strike through a combination of factors: some of the genes some people are born with appear to make those people more likely to develop Alzheimer’s than others; brain inflammation and other factors also appear to play a role. Studies of the human genome have found genetic overlap between the genes associated with Alzheimer’s and those associated with psoriasis, which also is believed to be driven by a combination of our genes and other elements.

In addition, evidence is increasing that some of the same cells (“Th1/Th17 cells”) are involved in the processes of both psoriasis and Alzheimer’s disease.

The latest study

A recent study examined the medical records of more than three million people in South Korea, including more than half a million psoriasis patients. They broke the people into three groups: subjects with psoriasis who had been treated with pills, injections, or infusions (known as “systemic” treatments); subjects with psoriasis who had not been treated with those drugs; and subjects without psoriasis who were matched with the other groups by age and sex, to try to make the groups comparable.

The systemic psoriasis treatments used by subjects in this study were acitretin (used commonly as a treatment in South Korea), methotrexate, cyclosporine, and biologic agents (like Enbrel, Humira, etc.).

Here are the key findings:

As compared to people without psoriasis, those with psoriasis who had not been treated with pills, injections, or infusions had a higher risk of developing Alzheimer’s disease; while those with psoriasis who had been treated with systemic treatments had the lowest risk of developing Alzheimer’s among the three groups studied.

The study was not designed to determine why these associations were present, but the authors theorize that systemic psoriasis treatments reduce inflammation that aids not just the skin but also whatever triggers Alzheimer’s disease.

It should be noted that both the increased risk and the decreased risk were “statistically significant,” but small. In America, about 10% of people age 65 or older have Alzheimer’s, and as many as one-third of people 85 or older may have the disease. Your psoriasis status, with or without systemic treatments, won’t change that risk much.

The study had several shortcomings. First is that it did not have information on the subjects’ family history of Alzheimer’s disease, one of the factors believed (along with age) to be a significant risk factor for Alzheimer’s. It also did not track other factors theorized by some to have an association with Alzheimer’s risk, including education status, smoking, and alcohol consumption.

The study had other interesting twists. Most notably, perhaps, it found that those with high blood pressure had a statistically lower risk of Alzheimer’s disease than those with normal blood pressure. Again, as with systemic psoriasis treatments, there could be some mechanism of blood pressure medicines that somehow reduces Alzheimer’s risk.

Another possibility, which we must always keep in mind with studies like this that compare large groups of people looking for associations among various factors, is that it could simply be random chance. No study requires 100% certainty; optimists suggest 1 in 20 study results is due to random chance; others have shown that far more than that turn out to be false. That is why it is safer to trust a result found in multiple studies done by different scientists, to reduce random chance (or sloppy work) from leading you astray.

Ultimately, the take-away from this study is probably that despite the risks we hear about in TV ads of psoriasis treatments, they may also, beyond clearer or clear skin, provide some other benefits still to be confirmed through additional studies.

[For more information on Alzheimer’s disease, consider visiting the U.S. National Institutes of Health Alzheimer’s disease web portal at www.alzheimers.gov. We also found this article fascinating on the possible role being played in Alzheimer’s by a bacterium involved in gum disease.]

[Last updated 5/3/2020]