Body mass index is associated with lumbar disc degeneration in young Finnish males: subsample of Northern Finland birth cohort study 1986

BACKGROUND The role of environmental factors in lumbar intervertebral disc degeneration (DD) in young adults is largely unknown. Therefore, we investigated whether body mass index (BMI), smoking, and physical activity are associated with lumbar DD among young adults. METHODS The Oulu Back Study (OBS) is a subpopulation of the 1986 Northern Finland Birth Cohort (NFBC 1986) and it originally included 2,969 children. The OBS subjects received a postal questionnaire, and those who responded (N = 1,987) were invited to the physical examination. The participants (N = 874) were invited to lumbar MRI study. A total of 558 young adults (325 females and 233 males) underwent MRI that used a 1.5-T scanner at the mean age of 21. Each lumbar intervertebral disc was graded as normal (0), mildly (1), moderately (2), or severely (3) degenerated. We calculated a sum score of the lumbar DD, and analyzed the associations between environmental risk factors (smoking, physical activity and weight-related factors assessed at 16 and 19 years) and DD using ordinal logistic regression, the results being expressed as cumulative odds ratios (COR). All analyses were stratified by gender. RESULTS Of the 558 subjects, 256 (46%) had no DD, 117 (21%) had sum score of one, 93 (17%) sum score of two, and 92 (17%) sum score of three or higher. In the multivariate ordinal logistic regression model, BMI at 16 years (highest vs. lowest quartile) was associated with DD sum score among males (COR 2.35; 95% CI 1.19-4.65) but not among females (COR 1.29; 95% CI 0.72-2.32). Smoking of at least four pack-years was associated with DD among males, but not among females (COR 2.41; 95% CI 0.99-5.86 and 1.59; 95% 0.67-3.76, respectively). Self-reported physical activity was not associated with DD. CONCLUSIONS High BMI at 16 years was associated with lumbar DD at 21 years among young males but not among females. High pack-years of smoking showed a comparable association in males, while physical activity had no association with DD in either gender. These results suggest that environmental factors are associated with DD among young males.