"We showed that the more weight that is lost, the greater the apparent benefit for preventing or delaying degradation of knee joints in osteoarthritis," senior study author Amanda Sainsbury, PhD, professor of obesity research at the University of Western Australia in Perth, says in an interview.
As an example, Sainsbury said a person who weighs 220 pounds and loses 22 “is likely to have double the benefit” of someone who loses 11 pounds.
In the study was published in the journal “Arthritis & Rheumatology.”
With knee osteoarthritis — also called wear-and-tear arthritis — shock-absorbing cartilage cushioning between the joints wears away, and the bones rub against each other more closely, causing stiffness, swelling, and pain that can limit mobility and lead to disability.
According to the CDC, osteoarthritis is the most common type of arthritis, usually occurring in the hands, hips, and knees. The disease affects more than 32.5 million adults in the United States, usually those over 50, but can occur in young people, too. Osteoarthritis has no cure, so doctors treat its symptoms with physical therapy, drugs, crutches or canes, surgery – and by prescribing a healthy diet and weight loss to reduce pressure on the joints, improve function, relieve pain, and slow joint damage
To study how changes in BMI may affect knee osteoarthritis, Sainsbury's research team analyzed X-rays of the knees of adult patients who took part in three independent studies in the United States and the Netherlands.
They divided the knee images into two groups: the "incidence cohort" of 9,683 knees from 5,774 people who, at the start of the study, did not have osteoarthritis structural defects; and the "progression cohort" of 6,075 knees from 3,988 people did.
The average age in both groups was around 60, around 60% of participants were female, and over 80% were white. But obesity between the groups differed: around 1/3 of the incidence group members were obese (defined as a BMI 30 or higher) vs. almost half of those in the progression group.
The researchers looked at data from the three studies and found that change in BMI over the 4 to 5 years was positively linked with both developing and worsening knee osteoarthritis structural defects, especially of the inner joints.
People With Normal Weight Saw Benefits, Too
People who lost 1 BMI unit lowered their odds of developing the structural defects of knee osteoarthritis by 4.76%. Those who lost 5 BMI units – a number that can take a person into a different category, such as from overweight to normal — reduced their odds by 21.65%.
"Weight loss is emerging as a suitable strategy for potentially preventing and delaying osteoarthritic degeneration of knee joints," lead study author Zübeyir Salis, BEng, a PhD student in Public Health at the University of New South Wales in Kensington, says.
Two Experts Not Involved in the Study Welcome Its Results
Eduardo Grunvald, MD, FACP, professor of medicine and medical director of the Weight Management Program at UC San Diego, calls the large sample size from three databases, long follow-up duration, and statistical analysis strengths of the study.
He would like to know, though, whether the BMI changes contributed to the knee changes or vice versa. "An individual’s worsening knee pain could lead to less physical activity and possible increased BMI.
"Long-term weight-loss maintenance is extremely challenging, and for optimal outcomes, medical professionals who treat joint disease should partner with clinicians trained to treat obesity," he says.
For Caroline M. Apovian, MD, co-director of the Center for Weight Management and Wellness at Brigham and Women's Hospital in Boston, this study is important because it refutes the notion that once you have “bone on bone,” a knee replacement is the only option.
"Providers can now safely recommend weight loss as a way to avoid knee replacement in certain cases," she says. "Weight loss will help at any stage."
Apovian would like to see similar studies in minority groups, to expand the usefulness of the results.
The authors are planning further related research. Because this study was not a randomized controlled trial, it showed a link between decreased BMI and improved outcomes, but not cause and effect. To show that, they need to conduct a randomized controlled trial.