Obesity and Osteoarthritis Pain Linked

By: Seth Hays for Shoulder1

Individuals suffering from obesity tend to have low thresholds for pain tolerance, a new study by Ohio State University professor of psychology Charles Emery suggests. The study included 62 people aged 50 to 76 years old who suffer from osteoarthritis, the most common form of arthritis. Approximately one third of the study’s participants were overweight.

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Quick Obesity and Arthritis Facts 21 million Americans suffer from osteoarthritis. According to the Arthritis Foundation, one cause for osteoarthritis is obesity 60 million US adults – or 30 percent – are obese. Among six to 19 year olds, 16 percent are considered overweight. The American Chronic Pain Association estimates one in three Americans suffers from chronic pain.

Emery’s research group wanted to pay close attention to weight and pain tolerance because only a few conflicting research studies exist that examine the link between pain and obesity. “Some studies say that obese people are more tolerant of pain, while other studies say they are less tolerant,” said Emery, who worked with on the research with colleagues from Ohio and Duke Universities.

How to Measure Pain

Participants in the study received small electric shocks to their left ankle at the sural nerve that extends into the calf. This type of electric stimulation causes mild tingling and pain. As the brain begins to perceive pain, it activates the muscles around the nerve, a response that moves the leg away from the cause of the pain. “This kind of evaluation is in some ways a more objective way of measuring the body’s response to pain,” said Emery, “as opposed to simply asking someone if they feel pain.”

Determined by body mass index (BMI) scores of 30 to 35 – a measurement to indicate a healthy weight by relating height to weight – obese participants had stronger reactions to the electric shocks than did non-obese participants.

After looking at these objective pain measurements, researchers then asked participants to fill out a questionnaire to determine the amount of pain each person felt subjectively. Interestingly, obese and non-obese participants perceived the same amount of pain, a finding that can have significant impact on the wellbeing of those who are overweight.

"This is important because if an obese person begins an exercise program, he may not cognitively experience pain when in fact it is hurting the body on some level," Emery said. Since the pain signals are not being reacted to, damage can ensue. “That could lead to severe pain down the road.”

These findings could be significant to a substantial portion of the population, since according to the Centers for Disease Control, 30 percent of all Americans age 20 and older suffer from obesity.

But the physical reaction to pain can be lessened with a little muscle relaxation training. After Emery’s group performed the first shock treatments, participants took a 45-minute coping skills lesson that included training in progressive muscle relaxation.

Afterwards, the participants received the same electric shocks and all had greater pain thresholds. But still, obese participants did not have as high a threshold as non-obese participants even though pain perception was the same.

“Our findings show the importance of looking at objective as well as subjective measurements of how the body responds to pain stimuli," Emery concluded.

Emery presented his findings in March at the American Psychosomatic Society conference in Denver.

Last updated: 07-Apr-06