A doctor examines a patient in a file photo. Sharma said doctors should routinely ask about pain when treating obese patients. Photograph by: Justin Sullivan , Getty Images

Obesity can cause not only mental anguish, but also physical pain, according to a survey of more than one million people in the U.S.

Appearing this month in the journal Obesity, the study found that overweight people reported 20 per cent higher rates of pain than "normal" weight, and the higher the body weight, the greater the pain.

The obese group reported 68 per cent higher rates of pain; those with extreme, or "class III obesity" — meaning a body mass index of 40 or more, one of the fastest-growing weight classes in Canada — reported 254 per cent more pain.

"People who are obese are considerably more prone to having daily pain," the authors write — and the association held after the team controlled for back, neck or other painful conditions.

According to the researchers, one plausible explanation is that excess fat is biologically active. It secretes leptin and other hormones that can cause inflammation throughout the body "that ultimately create states that result in pain."

Fibromyalgia, for example, is common in people with obesity; so are chronic headaches and migraines.

Chronic, daily pain affects every dimension of a person's life, says Dr. Arya Sharma, scientific director of the Canadian Obesity Network. "It affects your sleep, it affects your quality of life, your energy levels, your professional life.

"It's a major barrier for someone trying to manage their weight — and a major driver of weight gain in a lot of patients."

The study was based on a Gallup poll of 1,062,271 randomly selected adults interviewed between 2008 and 2010. People were asked to report their height and weight. They were also asked — among other questions related to stress, happiness and their emotional lives — "were you experiencing a lot of pain yesterday, yes or no?" Twenty-five per cent of the respondents were obese.

Overall, the team found that the odds of having pain escalated with each category of obesity.

The association between weight and pain held for both genders, but it was more pronounced in women, said co-author Dr. Arthur Stone, distinguished professor of psychiatry and vice-chair of psychiatry at Stony Brook University in New York, and a senior scientist with the Gallup Organization.

One of the study's main weaknesses is that it was a one-day assessment about what happened the day before, Stone said. But it was intended to reduce reporting problems that can occur when people are asked to report over longer periods of times, "Because they simply can't remember."

The survey's strength is its sheer size, said Sharma.

The study wasn't designed to answer what comes first: weight or pain. "But now we know there is a reliable relationship between weight and pain, and that wasn't nailed down before," Stone said.

"It suggests that people take this more seriously."

Sharma said doctors should routinely ask about pain when treating obese patients.

Currently, 62 per cent of the nation's adult population is either overweight or obese. The proportion of adults falling into "class III" obesity has increased tripled over the past three decades, from 0.9 per cent of the population in 1978-79, to three per cent in 2009.

skirkey@postmedia.com

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