Which Countries Have the Most Psoriasis?

Which Countries Have the Most Psoriasis?

I live in the land of poutine, hockey, maple syrup, moose, and “eh!” That is to say, I live in Canada. I remembered being told when I was younger that the incidence of psoriasis here in Canada was about 1%, but I started thinking the other day, what about the rest of the world? I was curious if the percentage of people with psoriasis was more or less even between countries, or if some global populations were more likely than others to have it?

I’ve got the whole world, in my hands

Let’s break it down globally. There are about 7.4 billion people in the world, and an estimated 125 million of them have psoriasis. That means about 1.7% of the population has psoriasis, which works out to 1 in 59 people. While psoriasis can feel very isolating, you are certainly not alone! Global trends indicate that countries further from the equator have a higher prevalence of psoriasis, that there’s a higher incidence in certain age brackets, and that there’s a fairly even distribution of psoriasis between men and women.1 For consistency, we’ll look mostly at the prevalence rates in adults.

North America

Do you ever hear a fact or statistic, and you just assume that it will always be true? I mentioned above that I had once heard that 1.0% of Canadians have psoriasis, because that used to be the figure. Turns out, we now sit closer to 2.75% of the population!1 (In a similar vein, I used to hear that 10-25% of people with psoriasis would get psoriatic arthritis, but I now commonly hear this figure reported as 20-40%. The times they are a-changing!). Whether that’s because incidence has gone up vs. there are simply more correct diagnoses now, I don’t know. An estimated 3% of American adults have psoriasis, which means we pretty much fall in line with our neighbors to the south.1

South America

Not as many studies looking at psoriasis prevalence have been done in South America, but we do have some data. Brazil has an estimated incidence of 1.3-2.0% and Mexico of 2.4%. Argentina, Colombia, Venezuela, and Chile all have an estimated prevalence of 2.0%.1,2 Keep in mind that it’s not clear whether these studies looked only at adults or psoriasis patients of all ages (when you include children into these cohorts the percentages tend to be lower because adults are more likely than children to have psoriasis).

Europe

Although Europe is one continent, the incidence of psoriasis is not uniform among European countries. In the UK, psoriasis incidence is estimated to be about 1.3%, which is among the lowest. Croatia sits closely, at 1.2%, but Denmark and Norway may have incidences as high as 3.7% and 4.8%, respectively. Italy is estimated at 3.1%, and France at a whopping 5.2%.1 Poland, Portugal, and Sweden are lower, at 1.4%, 1.9%, and 1.35%, respectively. Bear in mind that these statistics are to be taken with a grain of salt. They come from different studies that used different methodologies, and it stands to reason that if they were repeated with a different cohort those percentages would vary.1

Australia

Australia’s incidence of psoriasis is 2.3%. Pretty much in-line with North America, mate! (I suspect, perhaps cheekily, that at least half of these cases must be due to the stress of living with giant spiders).1

Africa and Asia

Africa and Asia have some of the lowest psoriasis rates in the world, but few studies exist that have looked only at the adult population. For prevalence in all ages, Sri Lanka and Japan sit at only 0.44%, Tunisia at 0.57%, Egypt at 0.19%, and Tanzania at 0.09%. One of the largest studies looked at 23 million people in China and Taiwan and found a combined incidence of only 0.2%.1,3

One unfortunate global trend is that the incidence of psoriasis is rising, but is there something we can learn from countries where the incidence is below 1%? Why might psoriasis sometimes be 5-10 times more common in Europeans than in Asians? In part, genetics plays a big role. There are up to 60 gene variations that have been identified as predisposing Caucasian populations to psoriasis, and some of these variations simply do not exist in Asian populations (for example). However, psoriasis is on the rise everywhere, and these increases cannot be entirely explained by genetics. Environmental factors like diet and daily stress are two of the most suspicious culprits. If those closer to the equator have less psoriasis, could sunshine or climate play a role as well? A great study to tease out these factors would be one that compared the incidence of psoriasis in a native population to the incidence of psoriasis in a group of genetically similar individuals who had immigrated to a different continent.1

What about you? Where do you think researchers should look to find these answers?

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