Your love for grilling meat may increase the risk of rheumatoid arthritis -- a chronic autoimmune disease where the immune system mistakenly attacks the cells lining the joints, warned a study.

It is due to the release of polycyclic aromatic hydrocarbons (PAHs) during the procedure.

These particles, which are environmental pollutants, form during the burning of coal, oil, gas, and wood, as well as during the flame grilling of meat and other foods, revealed the study, published in the journal BMJ Open. PAHs also originate from smoking tobacco.

"While PAH levels tend to be higher in adults who smoke, other sources of PAH exposure include indoor environments, motor vehicle exhaust, natural gas, smoke from wood or coal burning fires, fumes from asphalt roads, and consuming grilled or charred foods," researchers from the University of Maryland wrote in the paper.

"This is pertinent as households of lower socioeconomic status generally experience poorer indoor air quality and may reside in urban areas next to major roadways or in high traffic areas." These people may therefore be particularly vulnerable, they suggest.

The team studied a variety of toxicants, including PAHs, PHTHTEs (chemicals used in manufacturing plastics and consumer products), and volatile organic compounds (VOCs) derived from paints, cleaning agents, and pesticides.

They included nearly 22,000 adults, 1,418 of whom had rheumatoid arthritis, while the remaining 20,569 did not. The team gathered blood and urine samples to measure the total amount of PAH, PHTHTEs, and VOCs in the body.

They discovered that 7,090 participants had PAH in their system, 7,024 had PHTHTEs, and 7,129 had VOCs.

Regardless of their smoking status, the highest risk of developing rheumatoid arthritis was found among people with the top 25 per cent of bodily PAH levels. In particular, people with the PAH 1-hydroxy naphthalene in their bodies were 80 per cent more likely to have rheumatoid arthritis.

However, people with high levels of PHTHTEs and VOCs did not show an increased risk of rheumatoid arthritis.

Further analysis showed that bodily PAH levels accounted for 90 per cent of the total effect of smoking on rheumatoid arthritis risk.

The researchers noted that "this is an observational study, and as such, can't determine cause". And they also acknowledged limitations including that measurements of environmental toxicants in fat (adipose) tissue weren't available.

However, they said "To our knowledge, this is the first study to demonstrate that PAH not only underlies the majority of the relationship between smoking and (rheumatoid arthritis) but also independently contributes to (it). This is important as PAH are ubiquitous in the environment, derived from various sources, and are mechanistically linked by the aryl hydrocarbon receptor to the underlying pathophysiology of (rheumatoid arthritis)."