—By David Holzman

Two new studies published this spring have powerfully linked obesity and prescription opioid use. While previous research has connected the two conditions, back and joint pain may be the connecting force tying the two, according to the new research.

“While the obesity epidemic has been previously viewed as being disconnected from the opioid epidemic, it is clear that this is not the case,” said Andrew Stokes, PhD, an assistant professor in the Department of Global Health at Boston University School of Public Health.

Obesity and, more importantly, living in an environment that is not conducive to maintaining a healthy weight are a pathway into chronic pain and prescription opioid use, said Dr. Stokes, who is also the first author on the study published in American Journal of Preventive Medicine (AJPM 2020;58[6]:766-775). The other study was published in JAMA Network Open (2020;3[4]:e202012. doi: 10.1001/jamanetworkopen.2020.2012).

In the AJPM study, the investigators used data from the Medical Expenditure Panel Survey to examine the incidence of long-term prescription opioid use by obesity status.

Analyzing a data set of opioid-naive adults (N=89,629), the researchers found obesity was strongly associated with incident long-term prescription opioid use. That association skyrocketed from 24% (95% CI, 7%-44%) in overweight individuals to 158% (95% CI, 106%-224%) in those with class III obesity (body mass index [BMI], 40.0-49.9 kg/m²).

The team also found that about one-fourth (27%; 95% CI, 19.0%-34.8%) of all incident long-term opioid use in the United States was connected with a BMI above normal, posing the question whether long-term use could be averted if all overweight and obese individuals reduced their weight to normal levels.

The JAMA study is a cross-sectional study of a national sample of electronic health records for nearly 566,000 people ranging in age from 35 to 64 years. At baseline, 31.4% were overweight and 48.2% were obese.

All were examined by primary care physicians in the multipayor athenahealth network, between Jan. 1, 2015, and Dec. 31, 2017. Their BMIs were determined during 2016. The investigators also identified prescriptions for opioids occurring in the 365 days before and after the BMI measurements were taken. During those two-year periods, 16.6% of the patients were prescribed opioids.

The investigators found an association between obesity and prescription opioids that rose with BMI, according to the report. Overweight patients (BMI, 25.0-29.9 kg/m²) were 8% more likely to be prescribed opioids than normal-weight patients. Obese I (BMI, 30-34.9 kg/m²), obese II (BMI, 35.0-39.9 kg/m²), and obese III patients (BMI, 40.0-49.9 kg/m²) were 24%, 33% and 48% more likely to be prescribed opioids, respectively. Obese IV patients (BMI, 50-80 kg/m²) were 71% more likely to receive opioids.

The Back–Joint Pain Connection

In both studies, common pain diagnoses for patients prescribed opioids were similar. In the AJPM study, the researchers listed joint pain, back pain, injury, and muscle and/or nerve pain as the most commonly observed types of pain among adults with obesity and higher levels of opioid prescriptions. In the JAMA research, three pain diagnoses—osteoarthritis, “other joint disorders” and “other back disorders”—were the most prevalent among the 25 pain diagnoses, accounting for a combined total prevalence of 7%. Osteoarthritis and other joint disorders were the two indications for prescription opioids with the strongest associations with obesity.

Also in the JAMA study, the relative risk of being prescribed opioids to manage osteoarthritis was 1.90 (95% CI, 1.77-2.05), whereas it was 1.63 for other joint disorders. Both had stronger associations with obesity than the mean for any pain diagnosis.

“Joint and back disorders appear to be the most important diagnoses in explaining the increased receipt of opioid prescriptions among patients with obesity,” according to the researchers.

“The most important take-home point from these papers for clinicians is that obesity is a driving factor in the development of chronic pain conditions,” said Andrea L. Nicol, MD, MSc, FASA, an associate professor in the Department of Anesthesiology at the University of Kansas School of Medicine, in Kansas City, who was not involved in the research.

“I really was intrigued by the sensitivity analyses performed in the AJPM article, which showed that even when controlling for factors we know influence chronic pain, such as mental health disorders and smoking, the associations between obesity and opioid prescriptions held strong,” Dr. Nicol said.

“These are both very important papers,” agreed Peter S. Staats, MD, MBA, FIPP, ABIPP, the chief medical officer at the National Spine and Pain Centers, in Baltimore. “We have long since noted that the United States has a higher incidence of obesity as well as a higher incidence of addiction and opioid misuse compared to other industrialized countries.” Dr. Staats, also the president-elect of the World Institute of Pain, was not involved in the research.

What Physicians Can Do for Their Patients

For Dr. Stokes, the impetus for the research was the “lack of attention to the drivers of demand [for opioids].

“As this study demonstrates, obesity through its connections with chronic joint and back pain are driving demand for prescription opioid use, which may, in turn, lead to opioid misuse. Rather than thinking about how we can limit access to treatments for current pain patients, we as a society should be thinking deeply about how we can reduce demand for pain treatments in the future, through eliminating risk factors such as obesity.”

Physicians might change how they talk about obesity, particularly to younger people, including chronic pain as one possible associated outcome, Dr. Stokes explained. “It is important to respect and affirm all body types,” he said. “However, we also see that many youths are gaining obesity without choosing it, as a result of their environments, which presents a health inequity—since this will likely cause chronic pain.”

Focusing on treating the pain condition does not address the contributing factors to chronic pain, such as anxiety, depression, smoking status or obesity, Dr. Nicol said. “Ultimately, education, advocacy and intervention for obesity through nutrition, wellness and activity is a conversation that all clinicians need to have with their patients who have pain and are overweight or obese.”

The sources reported that both studies were funded by the Robert Wood Johnson Foundation.