How Overweight and Obesity Affect Psoriatic Arthritis
Excess weight plus PsA equals increased health complications. Excess weight plus PsA equals increased health complications.
Obesity and psoriatic arthritis (PsA) are an unhealthy mix. Research shows that people who have both conditions have a harder time controlling their PsA, which also tends to be more severe than in those who weigh less. Excess weight also adds to the risks of heart disease, stroke, diabetes and other metabolic conditions, which already increase with PsA.
In a 2015 study published in the Annals of Rheumatic Disease, for example, obese people with PsA were 48% less likely than their normal-weight counterparts to reach, after a year, a point of “minimal disease activity,” determined by measuring pain, tender or swollen joints, skin involvement and other factors. Being overweight rather than obese caused problems as well, lowering the odds of the desired response by 35%. (Study investigators defined normal as a body mass index [BMI] <25 kg/m2, overweight as a BMI >25 kg/m2 and obesity as BMI >30 kg/m2.)
The Fat-Inflammation Link
Exactly how fat affects PsA – and vice versa – is still unknown, says Dafna Gladman, MD, professor of medicine at the University of Toronto in Canada and co-author of the Annals of Rheumatic Disease study. She notes that fat tissue is metabolically active, releasing such inflammation-causing proteins as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and leptin.
These proteins, called cytokines, are already overactive in PsA, says Jon T. Giles, MD, MPH, assistant professor of medicine at Columbia University in New York City. “Fat tissue is a source of many of the same inflammatory cytokines that are produced by inflamed joint tissue in people with inflammatory arthritis,” he says.
Fat tissue may also be a second factor – along with PsA itself – contributing to autoimmunity. The immune system misfires in PsA and related conditions cause the body to turn its biochemical defenses against itself, Dr. Giles says.
Excess Weight Curbs Drug Response
In Dr. Gladman’s recent study, the heavier people were, the less likely they were to respond to either biologic drugs or traditional disease modifying anti-rheumatic drugs (DMARDs), a result found in a number of earlier studies. Higher weights were also linked to more severe skin problems, worse pain and a higher number of tender joints.
“When you are overweight, it’s difficult to figure out the dose of medication you might need,” Dr. Gladman says. “[Dosing of] Remicade is weight-related, but other drugs don’t have that, so obese patients may be undertreated because we don’t know the precise dose we should be using.”
Etanercept [Enbrel] and adalimumab [Humira], for example, are formulated to be given at a single, fixed dose regardless of a patient’s weight. Two studies of etanercept and adalimumab published in the Journal of the American Academy of Dermatology in 2006 and 2010, respectively, showed that obese people with psoriasis and PsA do not get as much relief from symptoms with the drugs as lighter-weight patients.
Weight Loss Benefits
Extra weight weighs down joints, causing biomechanical stress and damage. “Because you carry around more weight, especially in the lower extremities and back [common locations for PsA-related joint damage], there are additional forces at play,” Dr. Gladman says. Losing modest amounts of weight can make a big difference, as each pound lost takes four pounds of pressure off knees.
People with PsA are likely to have better outcomes with both DMARDs and biologics when they lose weight. Researchers for a 2014 trial published in Expert Opinion on Biological Therapy randomized people with psoriasis who were treated with a TNF-αblocker to either a low-calorie diet or to their regular diet. The low-calorie group, who lost at least 5–10% of their starting weight over 24 weeks, was 30% more likely to have a 75% reduction in involved skin area than those who maintained or gained weight. Trials with some DMARDs show similar results.
“Weight loss may improve the overall health of patients with PsA in the long-term, as well as increasing their chances of achieving remission of their disease,” Dr. Gladman says.