Parental Smoking and RA in Children

By Jane Farrell

Rheumatoid arthritis (RA) is a chronic disease that causes pain and swelling in the joints. It’s an autoimmune disorder, in which the immune system mistakenly attacks your own healthy joint tissues. Experts don’t know what causes the disease, but genes, environmental factors, and sex hormones are thought to play a role.

Smoking cigarettes is a well-established risk factor for developing RA. However, it’s unclear whether secondhand smoke, sometimes called passive smoking, also raises risk of the disease. The National Institute of Health (NIH) reports that a research team led by Drs. Kazuki Yoshida and Jeffrey A. Sparks of Brigham and Women’s Hospital and Harvard Medical School set out to investigate the link between secondhand smoke exposure over the lifespan and RA in adulthood.

The researchers looked at different categories of secondhand smoke exposure and RA risk. They examined the effects of maternal smoking during pregnancy, parental smoking during childhood, and living with a smoker as an adult. The study was supported by several NIH institutes, led by NIH’s National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) and National Cancer Institute (NCI). Findings were published in Arthritis and Rheumatology, on August 18, 2021.

The team analyzed data from nearly 91,000 women in a study of registered nurses, the NIH said in a news release. Participants completed health questionnaires every two years from 1989 to 2017. Researchers collected information about secondhand smoke exposure when the women were 35 to 52 years of age. Medical records were used to confirm RA diagnoses.

Over the almost three decades, 532 women developed RA, the NIH release reported. Of those, about two-thirds were “seropositive,” meaning that blood samples tested positive for certain types of antibodies directed against the body’s own proteins.

The researchers used statistical modeling to estimate the effect of secondhand smoke on seropositive RA risk. They were able to control for other factors like becoming a smoker as an adult. Parental smoking during childhood was associated with a 75% increase in risk of seropositive RA. This risk was even greater among those who smoked as adults.

No link was found between maternal smoking during pregnancy and adult RA risk after accounting for later smoking exposure. Similarly, the researchers found no evidence that living with a smoker as an adult directly increased RA risk, although a firm conclusion wasn’t possible because of the close correlation between living with a smoker and smoking as an adult.

“Our findings give more depth and gravity to the negative health consequences of smoking in relation to RA, one of the most common autoimmune diseases,” Yoshida says.

In infants and children, secondhand smoke is already associated with numerous health effects, including increased risk of respiratory infections, more frequent and severe asthma attacks, ear infections and SIDS. This study is among the first to suggest a direct influence of parental smoking on the development of RA. The team is planning to expand the study in the future to include both men and women.