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New research from Stanford University, published in the latest issue of Arthritis Research & Therapy, investigates the complex interactions between smoking and rheumatoid arthritis in men and women.
The controlled study of 2625 people showed a past history of smoking increased the risk of developing rheumatoid arthritis in men. However, female smokers did not have a greater risk of developing arthritis.
More common in women
Rheumatoid arthritis (RA) occurs when the body's immune system attacks the joints leaving sufferers in severe pain and with reduced mobility. It affects about two million people in the USA alone and is two to three times more common in women than in men. The causes of RA are poorly understood; but a number of factors are associated with an increased risk of developing the disease, such as obesity, diet, age and a history of smoking.
Read: Lifestyle factors linked to arthritis
Women's increased risk of developing RA is partly due to them outliving men, but this does not fully explain the differences in susceptibility to the disease. Previous studies have suggested that female sex hormones play a role in developing RA and factors such as taking the contraceptive pill and terminating pregnancies are also thought to increase the risk.
Given the gender-specific risks, Eswar Krishnan from Stanford University and his colleagues devised a survey to analyse men and women to see what effect smoking had on their chances of developing rheumatoid arthritis.
Rogue antibody
The researchers' study was case controlled, which means patients with RA were compared to healthy subjects. Data on age, height and education were collected, as well as details of gender and smoking habits to allow the researchers to discount other factors that may affect the risk of developing arthritis.
Read: Arthritis and travelling
Initial analysis of their data revealed smoking was only a risk factor for developing RA in men. To further investigate these differences the researchers examined the levels of rheumatoid factor found in their patients. Rheumatoid factor is a rogue antibody found in 80% of RA sufferers and is thought to stimulate the body's immune system to attack the membranes around the joints.
Smoking is associated with the production of rheumatoid factor, so it is not surprising that it should increase the risk of developing RA. However this study suggests that pre-menopausal women block this pathway, effectively knocking out the effect of smoking.
The results of this study uncover interesting differences between the susceptibility of men and women to the disease. The authors recognise the need for further research on the interactions between smoking, rheumatoid arthritis and gender if we are to reduce the number of people suffering from this debilitating disease.
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