Why do indigenous populations of South American Andes and indigenous Australian Aboriginals have little to no psoriasis in their populations yet their climates and terrain are vastly different?

We investigate the worldwide prevalence and incidence of psoriasis and psoriatic arthritis to try and understand how genetics and lifestyle play a role.

Psoriasis is worldwide although its prevalence varies, being generally more common in the colder north than in the tropics. In this article we share the population prevalence, shown as percentage of population that has psoriasis or psoriatic arthritis. The information on psoriasis per population is an estimate as only a handful of clinical population-based studies have been done. However, the facts remain the same; psoriasis and psoriatic prevalence is highest among Northern Europeans, and is almost entirely absent in aboriginal populations of South America and Australia.

Norway 4.2%

A prevalence of 4.2% were reported in a population-based health survey of 8045 Norwegian twins aged 19-31 years based on self-reporting. However, among the indigenous Sami of Norway, the prevalence has been estimated to 0.6 -1.4%.

Denmark 2.5 to 3.2%

In neighbouring Denmark, the prevalence was estimated to be 3.2% for men and 2.5% for women in a study of 3892 Danes interviewed by non-medical, professional interviewers.

Sweden 1.4%

In Sweden, the population prevalence was estimated to be 1.4%.

UK 2.8%

In the United Kingdom, the most recent study from reported that 633 people in a combined general practice database of 22,500 had one of the psoriasis diagnostic labels indicated, thus equating to a prevalence of 2.8%.

Croatia 1.55%

In other parts of Europe, a study from Croatia where a representative sample of 8416 was evaluated, 131 had psoriasis, giving a prevalence of 1.55%.

Germany 2.5 to 3.5%

Two surveys from Germany where adult patients were clinically examined revealed a prevalence of 2.5 in Hamburg (Northern Germany) and 3.5% in Augsberg (Southern Germany).

Italy 3.1%

A study in Italy using random sampling and a computer-assisted interview by trained interviewers of about 3660 subjects gave a prevalence weighted according to distribution of Italian population of 3.1% . The lowest prevalence was in Sardinia and the highest in Abruzzo.

France 3.58%

In France, based on a self-reported questionnaire-based survey, the prevalence of psoriasis in the French population over a 24 month period prior to the survey was estimated to be 3.58%.

Spain 1.43%

The prevalence in Spain, based on self-report of a random sample representative of the general population, was estimated to be 1.43%, with a higher prevalence in the central dry region of the country.

North America 2.5 to 3.15%

In North America, the prevalence of psoriasis was determined by patient interview as well as examination of standardised clinical photographs by two dermatologists; the estimated prevalence of diagnosed psoriasis was 3.15%.

Canada 2-3%

In Newfoundland, Canada the prevalence was estimated to be 2-3%.

Mexico 4.7%

Clinic-based studies from Mexico have reported a prevalence of 4.7%.

North America (African Americans) 1.3 to 2.5%

The prevalence of psoriasis among African Americans has been reported to be low. A recent study based on patient report of physician diagnosed psoriasis showed prevalence of 1.3% in African Americans, which was significantly lower than that in Caucasian Americans (2.5%). This reflects the data obtained from Europe and reflects the European ethnic origins of most North Americans.

Most African -Americans trace their origins from West Africa where the prevalence of psoriasis is lower than elsewhere in Africa.

West Africa

The prevalence of psoriasis in patients attending skin clinics in West Africa is reported to be:

• 0.08 -0.9% in Nigeria
• 0.4% in Ghana
• 0.05% in Mali
• 0.3% in Angola

East Africa

In East Africa as well as in ethnically mixed populations of Egypt and South Africa the reported prevalence is higher than West Africa with:

• 3.5% in Kenya
• 2.8% in Uganda
• 3% in Tanzania
• 3% in Egypt 3% 

South America among the lowest at 0.7%

The most striking study from South America reported that no case of psoriasis was seen during a comprehensive dermatological survey in 25,915 natives of the Andean region. The study examined inhabitants in various Central and South American regions of White, Black and Native ancestry and found that in an overall study population of 3140 subjects with skin diseases, psoriasis was seen in only:

• 0.7% in Guatemala
• 0.7% in Honduras
• 0.9-0.2% in different sites of Nicaragua

Prevalence reported from other South American countries is higher:

• 1.3% in Brazil
• 2% in Venezuela
• 4.2% in Paraguay

Caribbean

In the Caribbean, a clinic-based survey reported a high prevalence:

• 6% in Trinidad and Tobago
• 1.3% in Jamaica

Psoriasis was more common in persons of East Indian descent compared to those of African origin.

Australia nil to 2.57%

Similar to data from South America, no psoriasis was found among ‘full-blood’ Indigenous Australians after examination of some 3000 subjects in central, northern, and southern Australia.
The prevalence is higher in Caucasian Australians; a prevalence of 2.57% was reported among 25,296 patients seen in a private specialist practice in Melbourne, and 2.3% among 1037 subjects clinically evaluated in a population survey in Busselton.

South Pacific 0%

No psoriasis was seen in a population-based survey of 12,569 subjects in American Samoa in the south Pacific.

Asian Regions

Estimates from regions in Asia show that psoriasis is probably less prevalent in China and Japan than among those populations with European ethnicity. The reported prevalence in dermatology clinics in other countries are:

• 5.5% in Malaysia
• 3.1% in Kuwait
• 1.51 to 5.3% in Saudi Arabia

China 1.23%

Population-based surveys from China have given prevalence estimates ranging from 0.05 to 1.23%.

Taiwan 0.16 to 0.23%

A recent study from Taiwan reported a mean one-year prevalence of psoriasis was 0.23% for men and 0.16% for women, respectively in a nationally representative cohort of 1,000,000 individuals from the National Health Insurance database followed up for the years 2000 e2006.

Japan 0.29 to 1.18%

Clinic based studies from Japan have shown a similar low prevalence ranging from 0.29 to 1.18.

India 0.5 to 2.3%

The prevalence of psoriasis in patients seen in dermatology clinics in India ranges from 0.5% to 2.3%.

Summing it up

We can draw all sorts of conclusions and speculations from this information about genetic predisposition and environmental triggers. The article that is the source of this information gives more detail about historical information. What we can be sure of is that psoriasis and psoriatic arthritis occurs around the world, and is increasing in prevalence. This is all the motivation I need to keep looking for solutions to psoriasis among you, the psoriatic community.

References

Chandran V, Raychaudhuri SP. Geoepidemiology and environmental factors of psoriasis and psoriatic arthritis. J Autoimmun. 2010 May;34(3):J314-21. doi: 10.1016/j.jaut.2009.12.001.