Secondhand Smoke May Raise Kids’ Rheumatoid Arthritis Risk

Aug. 23, 2021 — Did your parents light up when you were a kid? If so, you may have a higher risk of having rheumatoid arthritis as an adult, a new study suggests. Researchers found evidence that women whose parents smoked had a 75% higher risk of having the disorder.

In people with rheumatoid arthritis (RA), the immune system attacks and damages joints, causing pain. The disease is fairly uncommon, affecting 1% or less of people, and most won’t develop it regardless of whether their parents smoked. Still, experts say the study matters because it provides more evidence of how being around secondhand smoke in childhood can have a lifelong impact on the immune system.

“The findings drive home the importance of reducing cigarette smoke exposure to reduce risk of disease,” said Milena A. Gianfrancesco, PhD, an epidemiologist at the University of California, San Francisco. “They highlight the need to not only focus on one’s personal smoking habits, but also other sources of secondhand smoke exposure.”

The researchers, whose study appeared Aug. 18 in the journal Arthritis & Rheumatology, tracked more than 90,000 women who joined the Nurses’ Health Study II in 1989 when they were between the ages of 25 and 42. At the study’s start, the average age of the participants was 35, and 93% were white. Almost two-thirds had never smoked themselves, and 65% said their parents had smoked during their childhoods.

The researchers discovered that about 350 of the women had developed RA over the next 3 decades. The researchers then tried to figure out if these women were more likely to have had parents who smoked.

The study authors estimated that childhood exposure to parental smoking boosted their risk of RA by 41%. The researchers also tried another statistical strategy, this one designed to account for the fact that many kids whose parents smoke go on to smoke themselves. This analysis suggested that having parents who smoked might raise the risk of RA by 75%.

So does this mean that women whose parents smoked are doomed to develop arthritis? Not at all. The overall rate of RA in the women in the study was around half of 1%, says Kazuki Yoshida, MD, the study’s lead author and an epidemiologist at Brigham and Women’s Hospital. And most of these women had parents who smoked when they were kids.

Why Might Exposure to Secondhand Smoke Boost the Risk of RA?

Exposure to secondhand smoke may irritate the lungs and cause abnormal proteins to form, Yoshida says. “The immune system produces antibodies in an attempt to attack such abnormal proteins. This immune reaction can spread to other body sites and attack normal tissues, including the joints.”

In addition, “smoking increases the risk of infections, which could in turn increase the risk of RA,” says Gianfrancesco, who wrote a commentary that went with the study. “Smoking is also known to result in changes surrounding the genome, which could trigger RA in susceptible people.”

Other studies have linked smoking exposure to autoimmune disorders. Earlier this year, researchers who tracked almost 80,000 French women reported that they found a link between exposure to smoking during childhood or adulthood and higher rates of RA.

The new study has limits. It says nothing about whether a similar risk exists for males. And the nurse subjects are overwhelmingly white, which means the results may not apply to women of other ethnicities.

Still, Gianfrancesco praised the study and says it relies on extensive data and strong statistical methods.

How can the findings be useful? According to Gianfrancesco, it’s important to understand that children with a family history of RA or other autoimmune disorders are especially vulnerable to the effects of secondhand smoke, because they already may be more susceptible to developing the diseases.

“Parents should keep their children away from secondhand smoke in the home or other environments in which smoke is prevalent, such as the home of another caregiver or a workplace if the child accompanies their parent to work,” she says.