Increased fat mass linked to high-intensity back pain

Increased back pain among people who are overweight or obese is specifically related to increased body fat content, reports a study in the September 15 issue of Spine. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

With further research, interventions to prevent increased fat mass may help to reduce the risks of back pain and related disability, according to the new study, led by Donna M. Urquhart, Ph.D., of Monash University, Melbourne, Australia. For her research, Dr. Urquhart was named winner of Spine's 2011 Young Investigator Award.

Increased Fat Mass Linked to Back Pain—But Which Comes First?

The study included 135 participants, ranging from normal weight to obese. All completed a standard questionnaire to measure low back pain intensity and related disability. They also underwent a test called dual-energy x-ray absorptiometry for detailed assessment of body composition, including measurement of fat and lean body mass.

The results showed that heavier people had higher levels of back pain intensity. For each five-unit increase in body mass index (BMI)—equivalent to the difference between being classified as overweight or obese—the odds of high-intensity back pain increased by 35 percent. For back pain disability, the association was even stronger: 66 percent per five-unit increase in BMI.

However, the increase in back pain at higher BMIs was specifically related to increased fat mass. For each five-kilogram (eleven pounds) increase in body fat mass, the odds of high-intensity back pain increased by 19 percent. For increased fat mass in the lower limbs, the increase was 51 percent.

In contrast, lean body mass was unrelated to back pain. Thus the increase in back pain intensity among people with higher BMIs was wholly related to their higher body fat content—not just the fact that they were heavier. People with higher body fat also had increased disability from back pain.

Back pain and disability were also related to specific patterns of body fat—including increased fat in the trunk area, around the abdomen (android fat mass), and around the hips, thighs, and buttocks (gynoid fat mass). On adjustment for possible confounding factors, "[N]o measures of lean tissue mass were associated with higher pain intensity or disability," Dr. Urquhart and colleagues write.

Low back pain is an extremely common problem that is usually "nonspecific"—unrelated to any spinal abnormality. Particularly with the rising obesity rate, it has been suggested that increased body weight may contribute to back pain. However, previous studies found only a weak relationship. The new study is the first to look at how back pain is related to more detailed measures of body fat—including specific patterns of fat and lean mass distribution.

The results show that greater fat mass is specifically associated with increased back pain and disability, while lean tissue mass is not. Several factors probably contribute to the link between fat mass and back pain, including greater mechanical demands on the spine. Metabolic factors related to higher fat mass—such as increased inflammatory activity—may also play a role.

Because of its cross-sectional design (participants studied once), the study can't determine which comes first: increased fat mass or back pain. Longitudinal studies (participants studied repeatedly over time) would be needed to determine whether higher fat mass predicts the later development of low back pain. If so, then measures to control body fat might be effective in preventing back pain and related and disability.

Spine's annual Young Investigator Research Award is open to all clinical and scientific researchers who are within 8 years of completion of their M.D., D.O., D.C., or Ph.D. The goal of the award program is to promote and recognize excellence in research on the spine, contributed by emerging investigators in any relevant discipline.