Experts do not understand exactly why some people get rheumatoid arthritis, but years of research suggest that the people most susceptible have:
- A genetic predisposition to RA
- Have been exposed to a harmful environmental factor (e.g. smoking)
- Experienced significant disruptions in hormonal balance
- An imbalance of intestinal microbes, which may be naturally ingrained or occur as the result of an infection or other event
Many researchers believe that RA is most likely to develop in people who have a genetic predisposition to RA and are exposed to certain environmental factors, experience hormone changes, and/or undergo intestinal microbial changes.
The specific gene associated with rheumatoid arthritis, HLA-DR4, is found in 60% to 70% of Caucasians with the disease. In contrast, it is only found in 20% of the general population.1
While presence of this specific genetic marker increases the likelihood of developing rheumatoid arthritis, it is by no means an accurate diagnostic tool. In fact, most physicians do not order this genetic test when diagnosing rheumatoid arthritis.
Environment and Lifestyle Factors
Day-to-day habits seem to have some influence over people’s risk of getting rheumatoid arthritis. The most established research in this area focuses on smoking, diet, and body weight.
Smoking and nicotine exposure
One of the greatest environmental risk factors for rheumatoid arthritis is exposure to nicotine, particularly smoking.
While the direct effect of smoking is not fully understood, it is believed that prolonged smoking plays a role in increasing the concentration of rheumatoid factor, which is an antibody (protein). The presence of rheumatoid factor in the blood is a sign that the immune system might be malfunctioning.
It is unclear exactly how diet affects the risk of rheumatoid arthritis. A large clinical study that followed 121,000 women for decades suggests that:
- Regularly drinking sugary sodas is associated with an increased risk of developing rheumatoid arthritis.2
- Eating a Mediterranean diet—which encourages eating vegetables, fruits, beans, and whole grains, does not affect women’s risk of developing rheumatoid arthritis.3
- Drinking coffee or tea (both caffeinated and uncaffeinated) is not correlated with developing rheumatoid arthritis.4
- Moderate consumption of alcohol does not seem to increase women’s risk, and may even lower it.5
People who are overweight or obese seem to have a greater risk of developing rheumatoid arthritis.6,7 (The results of one study suggest that being overweight increases the risk of RA for women but actually decreases the risk for men.8 More research is needed in this area.) In addition, people who are overweight seem to have worse symptoms than healthy-weight patients.9
Although smoking, diet, and weight influence a person’s overall risk of getting RA, there is not a direct link—the majority of people who are overweight and smoke will not get rheumatoid arthritis.
Disruption in Hormone Balance
The fact that women are more likely to get rheumatoid arthritis suggests hormones are a factor. This idea is further supported by the fact that the RA symptoms improve during pregnancy, only to flare up again after the birth. There is also evidence that women with irregular menses or who go through early menopause have an increased risk of RA.10,11
In addition to natural fluctuations in hormones, hormone medications and birth control seem to play a role. Oral contraceptives, which may contain doses of the hormone progestin or a combination of progestin and estrogen, have been correlated with a woman’s likelihood of developing rheumatoid arthritis.
Infection History and the Microbiome
Some scientists are researching the link between bacterial and viral infections and the development of rheumatoid arthritis. Clinical research suggests there may be associations between RA and certain infections, such as gingivitis, the Epstein-Barr virus, and chronic hepatitis C.12-15
In addition, some scientists have suggested that a person’s microbiome can influence the development of RA.10,11,16,17 A person’s microbiome is the collection of microorganisms, such as bacteria and fungi, living in the mouth, gut, airway and elsewhere on the body. These microorganisms have many roles, including influencing metabolism and the immune system.
Although experts have identified possible links between infection and the microbiome and RA, there is not enough evidence to point to clear causes and effects. More research is needed.