Diet may determine your risk for rheumatoid arthritis

Rheumatoid arthritis is the most common chronic autoimmune disease that affects the joints. RA has the potential for joint damage and deformity, with loss of function. The cause of RA is unknown. It affects people of all ages, and women more commonly than men. RA causes pain, stiffness and swelling, generally in multiple joints. RA may affect any joint, but the small joints in the hands and feet are most frequently involved. Rheumatoid inflammation may also develop in other organs such as the lungs.

The first study found that typical Western diets high in red meat, processed meat, refined grains, fried food, high-fat dairy, and sweets can increase a person's risk of developing RA in comparison to Prudent diets made mostly of fruit, vegetables, legumes, whole grains, poultry and fish.

"The evidence for diet having a role in the etiology of RA is inconsistent, sometimes conflicting. The prior studies based on individual nutrients and food groups may not have enough power to detect small effects," explains lead investigator in the study, Bing Lu, MD, DrPH; assistant professor of medicine; Brigham and Women's Hospital and Harvard Medical School. "Instead, overall dietary pattern analysis examines the cumulative effects of multiple nutrients and foods, and may be more predictive of disease risk than individual foods or nutrients. The single-nutrient approach may be inadequate for taking into account complicated interactions among nutrients, and high levels of inter-correlation makes it difficult to examine their separate effects. Therefore, we proposed a prospective study examining the overall effect of dietary patterns to furnish novel information about diet and etiology of RA."

Through the Nurses' Health Study II, -- a study of 116,460 female registered nurses ranging in age from 25 to 42 -- Dr. Lu's team followed 93,859 women without RA who filled out dietary questionnaires every four years between 1991 and 2011. From these questionnaires, the researchers discovered two dietary patterns among the women: Western and Prudent.

Throughout the course of the study, 347 women developed RA at an average age of 49. After taking into consideration their age, smoking status, body mass index, total calories consumed each day, alcohol consumption, level of physical activity, and socioeconomic factors, the women on Prudent diets had less of a chance of developing RA, while those on the Western diet were at increased risk, but BMI weakened these findings. "This indicates that the effects of the two dietary patterns on RA risk may be partially through BMI, and the clear mechanism is still unknown. Therefore, adherence to a healthy diet may be a way to prevent this debilitating disease, especially for high risk population," explains Dr. Lu of the findings.

The second study, showed that following the Dietary Guidelines for Americans can also lower one's chances of developing the disease. According to the United States Department of Agriculture, "the Dietary Guidelines for Americans … provide authoritative advice about consuming fewer calories, making informed food choices, and being physically active to attain and maintain a healthy weight, reduce risk of chronic disease, and promote overall health."

Little has been reported on how following these guidelines can impact one's risk of developing RA, so Dr. Lu's team again utilized the Nurses' Health Study II and food frequency questionnaires to determine if following these guidelines could lessen one's chance of developing RA.

In this study -- based on dietary intakes of various foods provided in the food frequency questionnaires, -- the Alternate Healthy Eating Index 2010 was created to measure how well the participants followed the Dietary Guidelines for Americans (2010), and the researchers observed associations of the diets of study participants and the likelihood of developing RA.

Looking at data from 1991 to 2011, 347 study participants self-reported a diagnosis of RA, which was later confirmed through their medical records. The researchers noted those who best adhered to the Dietary Guidelines for Americans (based on the Alternate Healthy Eating Index 2010) had a 33 percent reduced risk of developing RA when compared to those who did not follow the guidelines as closely. And, just as in the first study, the researchers noted that body mass index may be a modest intermediate factor linking diet and risk of RA.

Of those who developed RA, 215 had seropositive RA (diagnosed due to the presence of anti-cyclic citrullinated peptides or rheumatoid factor in blood work) and 132 had seronegative RA (an RA diagnosis, but one that is lacking definitive bloodwork). This led the researchers to further look into the difference between these two groups, and they found the association between following the dietary guidelines and the risk of developing RA was stronger among those with seronegative RA than those with seropositive.

"As we found with the first study, it is clear that a healthy diet may prevent RA development, and our team is interested in conducting further studies to look at why diet is associated with this risk," Dr. Lu concludes.