The Many Impacts of Obesity on Arthritis
A collection of studies show that excess weight makes various forms of the disease more likely and worse.
A special theme section in the January issue of Arthritis Care & Research examines the role of obesity on various forms of arthritis. Marian T. Hannan, editor of the journal, says there is a renewed focus on studying the role of excess fat on rheumatic diseases not only because of its significant impact, but also because of the potential to reverse some of the negative outcomes.
“As scientists and people who look to the future, we should be thinking: What are we going to do about that?” says Hannan. “What these articles do is describe and investigate pathways we should continue to follow, so we can untangle our knowledge and have a clearer picture of what to do next.”
Hannan notes that the 18 articles in the theme section touch on a cross section of rheumatic diseases, including osteoarthritis (OA), rheumatoid arthritis (RA) and psoriatic arthritis. Here’s a look at six of the studies and their findings.
Excess weight and racial differences
A study of more than 3,000 men and women, ages 45 to 79, who had knee OA or were at an increased risk of developing it, found that African-American women with a “high” BMI (25 or higher) or a “large” waist circumference (34 inches or larger) had worse disease outcomes over a four-year period than white women with the same characteristics.
“[The outcomes were] not just some global function score but really practical things – like, can you walk 20 feet, and how are you doing getting up and down from a chair – which is a really good measurement of your ability to use your lower extremities,” says Hannan, who was not involved in the research.
The study authors say the poor outcomes in African-American women may be due in part to additional factors – including other health conditions, depression and worse knee pain – and that by targeting these factors, the disparity can be reduced, but they say further studies are needed.
These findings dovetail with another recent study that found African-American women, compared with Hispanic and Caucasian women, have the highest lifetime risk of developing knee OA and needing joint replacement surgery.
What constitutes “obesity” in RA
Many patients with RA experience a shift in body composition that results in a higher fat-to-muscle ratio. Researchers tried to establish how this “overfat” state should be measured, especially when the patients are not all overweight or obese according to BMI or waist circumference (WC) measurements.
The researchers used three different measures – BMI, WC and dual X-ray absorptiometry (DXA), a technology that more accurately measures body composition – to classify 141 RA patients as obese or not obese. Twenty percent of women and 41 percent of men qualified as obese using BMI (30 or greater), while 32 percent of women and 36 percent of men qualified as obese using WC, and 44 percent of women and 80 percent of men qualified as obese using DXA.
To compensate for the discrepancy between obesity as measured by BMI and the more accurate DXA, Katz and her team recommend lowering the BMI cutoff point to qualify as obese among RA patients from 30 to 26.1 for women and 24.7 for men.
The researchers say the high percentage of overfat patients is troubling because there is a correlation between excess fat and worsening disease symptoms – such as increased pain and fatigue – as well as other health complications.
“Excess fat appears to have a relationship both with disease symptoms and also with cardiovascular risk. That’s why it’s important,” explains Patricia Katz, PhD, the lead study author and a professor in residence of medicine and health policy at the University of California, San Francisco. Adjusting the BMI cutoff would heighten practitioners’ awareness of a patient’s true risk of certain problems.
“For patients, I would get back to the message that you should try to increase your physical activity,” says Katz. “You can accumulate those physical activity minutes in shorter sessions, so you don’t have to go lift weights or go to the gym or to an exercise class. Just go for a walk.”
Weight gain and prednisone in early RA patients
A new study out of the Netherlands takes a closer look at the relationship between low-dose corticosteroid use and weight gain. To find out if prednisone is directly responsible for weight gain, the researchers assigned more than 200 adults with early RA (meaning they’ve had it for less than a year) to one of two groups. For two years, both groups had their disease tightly controlled with a methotrexate-based treatment strategy, but one group was also given a low dose of prednisone (10 mg/day) while the other was given a placebo.
After analyzing the results, the researchers found prednisone did not independently affect body weight. But it did suppress disease activity, which they say could lead to weight gain. Active, or uncontrolled, RA can result in weight loss, possibly due to loss of appetite and/or metabolic changes. Researchers also say it is likely the weight patients gained while on prednisone made up for weight loss they experienced when their disease was active and not well controlled.
Researchers say high doses of prednisone over long periods can cause weight gain. But they hope their results dispel concerns about relatively low doses of the drug, especially because the patients taking prednisone were found to have less pain and joint damage at the end of the study than the placebo group.
“Patients’ and doctors’ apprehension to use low-dose prednisone in early rheumatoid arthritis, because of its alleged weight-increasing effect, is largely unfounded, but could impede the start of this useful and cheap symptom-controlling and joint-sparing [drug],” says study author Maud S. Jurgens, a PhD candidate of the Utrecht Arthritis Cohort Study Group at the University Medical Center Utrecht, Netherlands.
Hannan agrees, and adds, “Keep taking the medications because they are your friends if you have early RA. They help you get better. But because you are feeling better you are actually going to regain weight you lost before.” She says a next step could be an intervention study of how patients can regain muscle mass instead of fat.
Gout prevalence and obesity
It’s well documented that obese people have a greater risk of having gout than those who aren’t obese. A new study quantifies that risk using information on more than 28,000 people from the National Center for Health Statistics (a division of the Centers for Disease Control and Prevention). The researchers found that – in an average American who is 5 feet 9 inches tall – for each 1-unit increase in BMI (approximately 6.8 pounds) the risk of gout goes up an additional 5 percent.
“The increased risk doesn’t just begin as you walk through the door of obesity, or step on the scale and find a weight that exceeds the obesity cutoff,” explains study author Allan Gelber, MD, an associate professor of medicine at Johns Hopkins University School of Medicine in Baltimore. “Even at ‘overweight’ levels, there’s a higher risk than those of normal weight.”
In fact, the researchers found those who are overweight (with BMI between 25 and 29.9) have a 50 percent greater risk of gout compared to those of normal weight (with BMI less than 25). That risk is doubled at the first level of obesity (BMI between 30 and 34.9) and three times higher at the second level of obesity (BMI of 35 or more). The elevated risk was seen in men and women as well as across racial/ethnic categories.
What’s more, the researchers say, the risk of gout remained elevated even when uric acid levels were taken into account, suggesting that high uric acid levels are not the only cause of the higher risk.
Dr. Gelber says this is an important reminder that extra pounds can increase your likelihood not just of getting diabetes and heart problems, but also having to deal with this painful condition. “Americans know that excess weight has an adverse health impact, but it also has an adverse impact in the determination of gout,” he says.
Psoriatic arthritis and prediction of minimal disease activity
This study looked at patients with psoriatic arthritis who started treatment with a tumor necrosis factor blocker (anti-TNF), a class of biologic that includes adalimumab (Humira), infliximab (Remicade) and etanercept (Enbrel). At the 12-month follow-up, about a third of the patients achieved minimal disease activity and stayed stable. Those who were obese (with a BMI greater than 30) were almost five times more likely not to achieve minimal disease activity than those of normal weight. Among those who did reach minimal disease activity in 12 months, those who were not obese were twice as likely to have maintained their status at the 24-month follow-up.
“Whether at 12 months or 24 months, it remains true. It’s at least a doubling of risk or protection. If you are obese, you have at least a doubled risk of having your disease flare up, and if you are of normal weight, you are at least two-fold more likely to maintain your minimal disease activity,” Hannan explains. “So, again, obesity has a negative impact across time on whether people’s psoriatic arthritis becomes active.”
Obesity’s link to the efficacy of anti-TNFs
This Italian study found that obese patients with longstanding RA who are put on anti-TNF therapies are less likely to achieve remission than their lighter-weight counterparts.
Hannan says that the next steps are to understand why and figure out which patients to focus on in order to make their lives better and their disease less severe. “We know people can lose weight and affect muscle mass at any age,” she says. “It’s not easy, but we know they can do it. So we know we can have a positive impact on obesity.”