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.