Mingling excess weight and osteoarthritis increases risk for
health problems.
By Emily Delzell
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.
Beyond Joints
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.”
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