Fat Mass, But not Lean Mass, Linked to Intense Back Pain

Patients with a higher body mass index (BMI) and more fat mass—but not lean mass—have a significantly greater risk of high intensity low back pain and disability, according to new research.

“Low back pain is the largest contributor to disability worldwide. The role of body composition as a risk factor for back pain remains unclear,” wrote the study authors, reporting in Arthritis Research & Therapy. “Our aim was to examine the relationship between fat mass and fat distribution on back pain intensity and disability using validated tools over 3 years.”

Patients were recruited through local media and public, private, and community weight loss clinics; they were not selected based on pain status. Those who had a past diagnosis of any arthropathy, previous knee surgery, and previous significant knee injury that required non-weight bearing therapy, analgesia, malignancy, or contraindication to MRI were excluded. Patients were eligible if they underwent DXA scan within one year of completing the Chronic Pain Grade Scale in 2008–2009; of 150 eligible patients, 123 repeated the same questionnaire three years later. Obesity and mental health were measured at the same time baseline back pain was assessed; mental health was evaluated using the Short Form 36 (SF-36) mental component summary (MCS). Patients also responded to the question, “On how many days during the last 14 days did you spend at least 20 minutes doing strenuous exercise such as bicycling, brisk walking, that was severe enough to raise your pulse rate or cause you to breathe faster?” Response options were “no days,” “1 to 2 days,” “3 to 5 days,” “6 to 8 days,” or “9 or more days.” The researchers defined “strenuous physical activity” as “undertaking strenuous physical activity for at least 20 min, on at least 1 or more days over the previous 14 days.”

Back Pain Risk Depends on Body Composition

Of the 123 patients who completed the study, mean age was 48.6 years, 78% of the cohort was female, and the mean BMI was 32.0 kg/m²—classified as obese. Overall, 31.7% of the study population reported high intensity back pain at baseline, follow-up, or both; 12.2% said they had persistent levels of high intensity back pain, 8.9% were developing high intensity back pain, and 10.6% had resolving back pain during the course of the study. Patients with high intensity back pain at any point during the study, compared to those who did not experience high intensity back pain, had a higher mean BMI [mean BMI (SD) for resolving pain 36.5 (7.5), developing pain 37.0 (9.5), persistent pain 36.4 (7.9), no high intensity back pain 29.7 (7.5); P < 0.001] and poorer mental health status [mean MCS (SD) for resolving pain 42.1 (15.6), developing pain 42.0 (16.9), persisting pain 40.5 (15.0), no high intensity back pain 48.9 (11.7); P = 0.003].

The researchers further observed that body composition—not just BMI—played a role in back pain: “In relation to body composition measures, those who had experienced any high intensity back pain during the study had higher mean total, truncal, upper limb, lower limb, android, and gynoid fat mass at baseline, than those without any high intensity back pain during the study [mean total body fat mass (SD) 46.4 (16.4) for resolving pain, 45.7 (14.6) for developing pain, 43.1 (14.6) for persisting pain, and 31.6 (16.1) for no high intensity back pain] (all p < 0.001). Similarly, those with any high intensity back pain had a higher fat to lean mass ratio than those without any high intensity back pain [mean (SD) total fat to lean mass ratio 0.9 (0.3) for resolving pain, 0.9 (0.2) for developing pain, 0.9 (0.3) for persisting pain, and 0.7 (0.3) for no high intensity back pain] (p = 0.0001).” Additionally, compared to patients who did not experience high intensity back pain, those who did report it had a greater risk for high disability back pain. The authors found no connection between baseline lean tissue mass and high intensity back pain.

The researcher wrote in their conclusion, “This longitudinal study shows that all DXA measures of fat mass across several different body regions (total, upper limb, lower limb, truncal, android, and gynoid) were associated with a significantly higher risk of high intensity back pain and disability over 3 years, whereas there was no significant relationship for lean tissue mass. The results of this study suggest targeting specifically a reduction in fat mass (not just simply weight loss) to prevent back pain, particularly in those who carry excess fat in the android distribution.”