A new study suggested that worsening air pollution aggravates the symptoms of rheumatoid arthritis, according to The Economic Times.

The study, which was conducted by the All India Institute of Medical Sciences (AIIMS), looked at 500 rheumatoid arthritis patients who have been living in New Delhi, India, for more than 10 years. The researchers found that the patients' symptoms, such as swelling of and pain at the joints, worsened during November and December, the months when there was an increase in suspended particulate matter (SPM) 2.5 in the atmosphere.

"We collected data on air quality from the Indian Meteorological Department in New Delhi for the past few years and then tracked patients undergoing treatment for rheumatoid arthritis here at AIIMS," said Uma Kumar, department head and professor of Rheumatology Medicine at AIIMS, according to The Hindu. "It was found that when the particulate matter in air was high, more disease activity was found in the patients."

AIIMS's report was released before the celebration of #WorldArthritisDay on Oct. 12.

Arthritis or other types of rheumatic disease affect 12 to 18 percent of the population in India. The increasing number of arthritis patients could be attributed to urbanization and lifestyle changes in recent years. Many people who are unaware of the condition tend to delay treatment and suffer from complications or even death, according to The Hindu.