“These chemicals can influence the development of OA,” explains Jeffrey N. Katz, MD, a professor of medicine and orthopaedic surgery at Harvard Medical School and Brigham and Women’s Hospital in Boston.

This effect can be seen in the numerous studies that have linked extra weight to hand OA. “Obviously, you don’t walk on your hands, so there may be something that is produced by fat cells in the body that causes the joint to break down more rapidly than it might otherwise,” says David Felson, MD, a professor of medicine and epidemiology at Boston University School of Medicine.

For both reasons – excess joint stress and inflammatory chemicals – fat should be kept in check among all people, especially those who already have OA.

Fat and Rheumatoid Arthritis

What It Is

Rheumatoid arthritis, RA, affecting 1.5 million Americans, is an autoimmune disease in which the body’s immune system attacks its own joint tissue. This creates inflammation throughout the body, and can lead to joint erosion and pain.

Why Obesity Matters

The inflammatory chemicals from fat that may play a role in OA are also culprits in RA. Some of these chemicals, called cytokines, can impact different body systems, including musculoskeletal and cardiovascular systems. Many types of cytokines are released by fat tissue, and researchers are working to identify them and understand the specific effects of each kind.

One important group is called adipokines, and most types of adipokines promote inflammation – “not a good thing in RA,” says Jon Giles, MD, an assistant professor of medicine in the division of rheumatology at Columbia University College of Physicians and Surgeons, in New York City.

Other cytokines released by fat include tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1). Both are overactive in RA and cause inflammation. You may be familiar with the biologic drugs that suppress them, including etanercept, brand name Enbrel, and infliximab, brand name Remicade, which target TNF-alpha, and anakinra, brand name Kineret, which targets IL-1.

One type of adipokine, called adiponectin, is good for the heart, because it has an anti-inflammatory effect on blood vessels – but it causes inflammation in joints. When people gain weight, they make less adiponectin, which may be one reason overweight RA patients can have less joint damage than those who are not overweight. But don’t think that means being overweight has a protective effect, says Dr. Matteson of the Mayo Clinic. “In fact, you are still at risk for your arthritis to advance more rapidly in your weight-bearing joints simply because of the biomechanical forces that come into play.”