Patients residing closer to equator develop rheumatoid arthritis earlier
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Key takeaways:
- People living in countries closer to the equator develop RA at an earlier age.
- The latitude gradient appears to be associated with socioeconomic status, according to researchers.
Individuals who live closer to the equator develop rheumatoid arthritis at a younger age, a link that is likely explained by socioeconomic status, according to data published in the Annals of the Rheumatic Diseases.
“In the international METEOR registry, we combine data from rheumatoid arthritis and spondyloarthritis patients from many different countries worldwide,” Sytske Anne Bergstra, PhD, of Leiden University Medical Center, in the Netherlands, told Healio. “When comparing this data, we noticed a large difference in age at onset of rheumatoid arthritis patients in different countries. Since we could not explain this difference, we decided to dive into the data.”
To investigate the correlation between latitude and the risk for developing RA, Bergstra and colleagues analyzed the METEOR registry, which includes information from patients with RA from North America, South America, Europe, Asia and Africa.
The primary outcome was the age of onset for RA, while the date of symptom onset acted as the secondary outcome. On the patient level, the researchers collected and analyzed data on patients’ gender, rheumatoid factor status and smoking status, as well as the presence of anti-citrullinated protein antibodies. In addition, Bergstra and colleagues collected information on health expenditure per capita, life expectancy, gross domestic product (GDP) and income levels for all represented countries.
The analysis included a total of 37,981 patients from 93 hospitals in 17 countries. For each per-degree increase in countries’ latitude, the average age at RA diagnosis increased by 0.23 years (95% CI, 0.095-0.38), according to the researchers. This resulted in a difference of more than 10 years, on average, at the age of disease onset. When the researchers accounted for socioeconomic factors, the average increase in the average age at RA diagnosis changed from 0.23 years to 0.051 (95% CI, -0.37 to 0.38) for every per-degree increase in latitude.
“RA starts at a younger age in people living at lower latitudes — ie, closer to the equator,” Bergstra said. “We showed that this could not be explained by differences in patients — eg, genes — but instead observed a direct link between the level of socioeconomic welfare of the countries people were living in and the time of onset of RA.
“Our study is an example of how mutually reinforcing factors work towards inequity,” she added. “People in low-income countries will not only get RA at a younger age, with an inherently longer disease course and a worse prognosis, but they also face poorer health care conditions and social support, which will further deteriorate their prognosis.”
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