Sleeping habit and other life styles in the prime of life and risk for ossification of the posterior longitudinal ligament of the spine (OPLL): a case-control study in Japan

BACKGROUND: Although the average age of onset of ossification of the posterior longitudinal ligament of the spine (OPLL) is at around 50 years, the onset of the symptoms is insidious and the progression is very slow. The etiology of OPLL has not been elucidated in detail. Previous studies have suggested that a high-salt diet and low consumption of animal protein, glucose intolerance and high body mass are risk factors for OPLL. However, there is little information about the relationship between OPLL and life styles in the prime of life (between 30 and 50 years). METHODS: To facilitate early prediction and prevention of OPLL, we analyzed life styles such as sleeping habit, physical exercise, smoking, alcohol drinking and hangover in subjects in the prime of life. Self-administered questionnaires were obtained from patients with OPLL and their sex- and age-matched controls. Sixty-nine patients diagnosed with OPLL within 3 years previously and 138 sex- and age-matched controls without backbone diseases, randomly selected from participants in a health checkup in a local town, were enrolled. RESULT: Moderate amount of sleep (6-8 hours vs. 5 hours or shorter and 9 hours or longer; odds ratio [OR] = 0.18, 95% confidence interval [CI] = 0.06, 0.54) and a regular sleeping habit (i.e., going to bed and getting up at regular time) (OR = 0.44, 95% CI = 0.22, 0.90) were associated with a decreased risk of OPLL even after adjusting for other factors. On the other hand, moderate physical exercise (once a week or more v.s. less than once a week: OR = 0.97, 95% CI = 0.42, 2.26), smoking (OR = 1.41, 95% CI = 0.67, 2.97), drinking (OR = 1.08, 95% CI = 0.53, 2.20) and hangover (OR = 1.12, 95% CI = 0.43, 2.94) in the prime of life showed no correlation with risk of OPLL. CONCLUSION: Good sleeping habits in the prime of life may decrease the risk of OPLL.