According to one of the world’s largest studies (Arthritis & Rheumatism, published online) assessing lumbar disc degeneration on MRI, investigators have noted that elevated body mass index (BMI), in particular overweight and obese individuals, is significantly associated with a greater number of levels with disc degeneration, global severity of disc degeneration, and end-stage disc degeneration with disc space narrowing.
In the study, the lumbar spine of 2,599 Southern Chinese volunteers (1,040 males and 1,559 females; mean age 41.9 years) was assessed with T2-weighted MRI for the presence of disc degeneration. Objective weight and height data were also recorded for each individual as were various demographic, lifestyle and environmental factors. To allow for ethnic variations in body fat distribution and disease risk between Caucasians and Asians, lead author Dino Samartzis (Department of Orthopaedics & Traumatology, University of Hong Kong , SAR, China) and his fellow authors used Asian-modified BMI categories to define BMI scores for being “underweight” (<18.5kg/m2), “normal weight“ (18.5–23kg/m2), “overweight” (23–27.5kg/m2), and “obese” (>27kg/m2). In their analysis, adjusting for various factors associated with disc changes, the authors noted a linear dose-response between weight categories (ie. underweight, normal weight, overweight, obese) and disc degeneration.
According to Samartzis et al, the link between elevated BMI and lumbar disc degeneration has been contentious. They wrote: “Some studies have suggested that elevated BMI, in particular being overweight and obese, may be related with disc degeneration, but such an association remains to date largely speculative with several studies adamantly opposing such a link.” They added that uncertainty over the link has been attributed to various factors, including lack of large epidemiological studies and improper study designs. Another reason why some studies have not found a link is the lack of advanced imaging, such as MRI to assess subtle disc changes.
At present, the exact mechanism behind the association between being overweight or obese and disc degeneration is speculative. Samartzis et al reported: “For numerous years, it has been postulated that overweight and obesity contribute to the compressive loading of the disc leading to disc degeneration. However, recent studies have noted that degenerative changes can also occur in non-weight bearing regions of the body.” They added that such findings are independent of increased loading effects and possibly contradict the idea that increased body weight contributes to degenerative changes due to altered biomechanics. The authors noted that elevated BMI, or overweight and obesity, may affect the loading on the disc, but one should not discount other potential mechanisms, such as low-grade inflammation from fat cells and altered metabolism that could affect disc health. The authors hope that their current study will motivate clinicians and researchers to address the effects of weight gain upon the spine more thoroughly.
Of further interest, based on their population-based study, the authors have noted that disc degeneration, more importantly its severity, is significantly associated with the development of low back pain. As such, Samartzis noted that “Since overweight and obesity are worldwide concerns whose prevalence continues to rise, our study’s findings have considerable public health implications. If these issues continue to plague society, they can further affect spine health leading to low back pain and its consequences.” Fellow investigator Kenneth Cheung, Department of Orthopaedics & Traumatology, University of Hong Kong, SAR, China, further added that “a deeper understanding of how elevated BMI contributes to disc degeneration and low back pain could potentially aid in the development of novel interventions that can improve quality of life for those with these disabling conditions.”