Unhealthy Mix: Obesity and Osteoarthritis
Mingling excess weight and osteoarthritis increases risk for health problems.
The link between being overweight or obese and having osteoarthritis (OA) in weight-bearing joints is fairly easy to understand, though it may be underestimated. Being just 10 pounds overweight puts an extra 30 to 60 pounds of pressure on the knees, for example.
“If you think about all the steps you take in a day, you can see why [being overweight or obese] would lead to premature damage in weight-bearing joints,” says Eric Matteson, MD, chair of the rheumatology division at the Mayo Clinic in Rochester, Minn.
But carrying extra bodyweight in OA does more than create a harmful load on joints. Excess fat also acts in non-mechanical ways to speed the destruction of cartilage and joints, says Peter van der Kraan, PhD, head of experimental rheumatology at Radboud University Medical Center in Nijmegen, the Netherlands. Fat is chemically active and constantly releases inflammation-causing proteins and other biochemicals, such as tumor necrosis factor-α and interleukin-1.
Inflammation and OA
“These proteins travel through your whole body and make it a little inflamed everywhere, including in your joints,” he says. “This constant, low-grade inflammation in your body makes your joints more vulnerable to developing OA, not only in those that are directly loaded by your weight, but also in joints that are not loaded by weight, like the joints in your hands.”
Hand OA is about twice as common among obese people as it is in leaner individuals, he says. Being obese also increases the chances that, once you have OA in a joint or joints, you will develop more OA elsewhere. Obese people with OA in one knee, for example, are five times more likely than healthy-weight people to develop OA in the other knee.
Excess fat tissue not only creates a constant state of low-grade inflammation throughout the body, but, by placing a mechanical load on cartilage and bone, it “activates” those structures, prompting them to release inflammatory protiens and other factors that cause joint destruction, says van der Kraan.
Obesity-related damage in OA is not limited to joints. In a 2015 Rheumatology review, van der Kraan detailed the links among obesity, OA and metabolic syndrome. People with OA are almost three times more likely than those in the general population to have metabolic syndrome – a group of conditions, including high blood pressure, high blood sugar, abnormal cholesterol levels, and excess fat around the waist – which is linked to increased risks of heart disease, stroke and diabetes. This association remained strong (though not as high) when the scientists controlled for obesity.
Some researchers, in fact, call the combination of obesity and metabolic syndrome “metabolic OA,” a distinct and dangerous subtype of OA. When these combine, it is a warning sign that should prompt a close look for heart disease, says Francis Berenbaum, MD, head of the department of rheumatology at the Pierre and Maries Curie University in Paris, France, who is studying age-related joint diseases and metabolism.
“When OA is linked to the metabolic syndrome it aggravates cardiovascular diseases linked to metabolism, such as atherosclerosis, probably through an increase in obesity-related inflammation,” he says. “Additionally, the risk for pain, worsening of OA and the need for [total joint replacement surgery] increase with each component of the metabolic syndrome a patient has.”
Fat is Disabling
Being overweight or obese makes the effects of OA more disabling, says John Batsis, MD, associate professor of medicine at the Dartmouth-Hitchcock Medical Center in Lebanon, N.H.
In a 2015 Scandinavian Journal of Rheumatology study, Dr. Batsis and his colleagues analyzed data from the Osteoarthritis Initiative, a study of about 5,000 people with knee OA. Compared with healthy-weight people with OA, they found that people with OA who were obese needed to take more medications, walked more slowly, were much less likely to be physically active and were at significantly higher risk after six years of developing disabilities that interfere with daily life.
“People who were overweight rather than obese had declines compared to those with a normal BMI [body mass index]; however, they were less than those observed in the group with obesity,” he says. “What this tells us is that we should encourage lifestyle modification to patients under the guidance of their clinician so they can safely and effectively lose weight to prevent long-term decline in physical function and risk of disability in the future.”