People who are overweight or obese when diagnosed with rheumatoid arthritis (RA) may be less likely than those of a normal weight to improve with medication, according to research from Sweden.
The link between a person’s weight and their RA symptoms is not simple. We know that having excess body fat can affect how the body’s immune system works, which may have implications for conditions like RA (where the immune system attacks the body rather than just protecting it). But we’re not really sure what those implications might be.
We also know that excess body fat can cause inflammation in some of the body’s tissues. But some people with excess body fat produce higher-than-normal amounts of cortisol, a substance with a strong antiinflammatory effect. So just how does body weight affect RA?
Previous research has suggested that people with RA who are overweight or very overweight (obese) are less likely to improve in the long term than people of a normal weight. Studies have also found that people with RA who are overweight don’t do as well when treated with anti-TNF drugs such as infliximab. But these studies didn’t look closely at people in the early stages of RA, and they couldn’t tell us clearly about how well people who were overweight did when treated with methotrexate, one of the most common medicines for RA.
WHAT DID THE RESEARCHERS HOPE TO LEARN?
In this new study the researchers wanted to know whether people who were overweight when first diagnosed with RA were less likely to respond well to treatment than people of a normal weight.
WHO WAS STUDIED?
This study included just under 500 people in Sweden who were recently diagnosed with RA. At diagnosis most people began treatment with DMARDs (disease-modifying anti-rheumatic drugs), usually methotrexate.
HOW WAS THE STUDY CONDUCTED?
At the start of the study the researchers measured the participants’ disease activity score (their DAS-28). They also weighed and measured them to work out their body mass index (BMI). A person’s BMI is a single number that relates their weight to their height. A BMI of 18.5 to 24.9 suggests a person is at a normal weight. A BMI of 25.0 to 29.9 suggests they are overweight, and a BMI of 30 or more
suggests they are obese.
The participants completed questionnaires about their background and lifestyle so that the researchers could adjust their findings to take into account things that can affect someone’s DAS-28, including their sex, whether they smoked, their social and economic status, and how much exercise they took. The researchers then measured everyone’s DAS-28 again after three and six months. They looked to see whether the people who were overweight at diagnosis had responded better or worse to treatment with
DMARDs than those of a normal weight.
WHAT DOES THE NEW STUDY SAY?
After six months, people who were overweight at diagnosis were less likely to have responded well to treatment than people of a normal weight. People who were overweight were:
- About half as likely to have achieved what the researchers called ‘low disease activity’ (defined as DAS-28 of
no more than 3.2)
- Almost half as likely to have achieved remission (DAS-28 of less than 2.6)
- Almost half as likely to have had a ‘good response’ to treatment (DAS-28 of no more than 3.2, and an improvement of at least 1.2).
HOW RELIABLE ARE THE FINDINGS?
This study used sound methods and its findings should be fairly reliable. One major strength of this research is that it was a population-based study. This means that it looked at how well people responded to treatment in their real lives, outside of the setting of a drug trial, which can be somewhat artificial and not always give the most useful information.
WHAT DOES THIS MEAN FOR ME?
Unlike previous studies that looked at how being overweight might affect RA treatment overall, this research looked mainly at people taking methotrexate. So we now know that there may be a link between being overweight and how well methotrexate works in treating RA.
But this study can’t tell us exactly why people who are overweight at diagnosis don’t do as well on the drug. Is it that being overweight makes RA worse? Or does having excess body fat affect methotrexate’s ability to relieve symptoms and reduce disease activity? Either way, the next step is to find out whether losing weight could improve treatment response for people who are overweight. If future studies find that it can, it could mean the possibility of a better prognosis for many people. Of course, losing weight isn’t easy. But a possible reduction in disease activity, pain and swelling could be a powerful motivator.
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Date summary prepared: November 2014
Summary based on research article published on: 12 May 2012
From: Sandberg, M E C, et al. Overweight decreases the chance of achieving good response and low disease activity in early rheumatoid arthritis. Ann Rheum Dis 2014;73:2029-2033 doi:10.1136/annrheumdis-2013-205094
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