Men who smoke are more susceptible to rheumatoid arthritis but there is no such link in women. Researchers at Stanford University investigated the impact of smoking on RA risk by studying a group of patients with the condition and comparing them with healthy controls. Smoking turned out to be a risk factor only in men. This may be because smoking increases the levels of a rogue antibody called rheumatoid factor, which is linked with RA. The study suggests that women are able to block production of RA, perhaps with female sex hormones. The link between gender, smoking and RA should be further investigated, the researchers say.