Magnetic resonance imaging (MRI) data show that obesity is associated with increased lumbar disc degeneration, according to a study published online January 30 in Arthritis & Rheumatism.

Low back pain (LBP) is a widespread and important cause of lost work time, diminished quality of life, and psychological distress. Lumbar disc degeneration, which can be readily observed by MRI, is known to be associated with LBP.

To address whether lumbar disc generation is associated with overweight and obesity, senior researcher Kenneth M.C. Cheung, MBBS, MD, from the Department of Orthopedics and Traumatology, University of Hong Kong, and colleagues conducted a population-based cross-sectional study in a southern Chinese population of 2599 individuals (1040 men, 1559 women; mean age, 41.9 years).

Participants were assigned to Asian-modified body mass index (BMI) categories and assessed by using sagittal T2-weighed MRI examinations of the lumbar spine.

MRI revealed disc degeneration in 1890 (72.7%) participants. Those with lumbar disc degeneration had significantly higher BMIs than those without degeneration (23.3 kg/m2 vs 21.7 kg/m2; P < .001).

The researchers noted an increase in degeneration with elevated BMI. Degeneration scores were defined as: no signal changes (0), slight decrease in signal intensity of the nucleus pulposus (1), hypointense nucleus pulposus with normal disc height (2), and hypointense nucleus pulposus with disc space narrowing (3).

Underweight individuals had an average score of 1.4, normal-weight individuals had an average score of 2.5, overweight individuals had an average score of 3.3, and obese individuals had an average score of 3.8. The differences between each group were statistically significant, with the exception of overweight-obese (underweight-normal weight, P < .001; normal weight-overweight, P < .001; and overweight-obese, P = .092).

In each category, the mean number of vertebrae with end-stage disc degeneration and disc space narrowing of the lumbar spine were, for underweight patients, 0.2 (range, 0 - 2; standard deviation [SD], 0.5); normal-weight patients, 0.3 (range, 0 - 4; SD, 0.6); overweight patients, 0.4 (range, 0 - 4; SD, 0.7); and obese patients, 0.5 (range, 0 - 4; SD, 0.9). The difference was not statistically significant between underweight and normal (P = .322), but it was statistically significant for normal-overweight (P < .001) and overweight-obese (P = .012).

In a multivariate logistic regression analysis, adjusted for age, workload, Schmorl's nodes, previous lumbar injury, and vertebral marrow changes, the researchers found a positive linear trend (r2=0.99) between BMI categories and disc degeneration (normal weight: reference; underweight: odds ratio [OR], 0.59 [95% confidence interval (CI), 0.41 - 0.84]; overweight: OR, 1.30 [95% CI, 1.03 - 1.62]; obese: OR, 1.79 [95% CI, 1.17 - 2.74]).

Obese individuals were more likely to suffer from end-stage disc degeneration with disc space narrowing (normal weight, reference; adjusted odds ratio, 1.72; 95% CI, 1.23 - 2.41).

Limitations to the study included that it was based on a southern Chinese population and may not be generalizable to other populations. The study was also cross-sectional, and further prospective studies will be needed to demonstrate that overweight and obesity cause disc degeneration. "[O]ur study is the first to the author's knowledge to note that elevated BMI values are significantly greater in individuals with disc degeneration compared to individuals with non-degenerated discs," conclude the authors. "[A]s this study is population-based, it is of tremendous public health importance."

The authors have disclosed no relevant financial relationships.

Arthritis Rheum. Published online January 30, 2012.

Jim Kling • Medscape Medical News © 2012 WebMD, LLC