Background: There are limited data examining the relationship between serum vitamin B12 levels and sleep.

Objectives: To assess vitamin B12 levels in unselected patients from primary care and to investigate possible correlations with sleep quality, insomnia and daytime sleepiness.

Methods: In this cross-sectional study, 512 consecutive patients were included.  Anthropometric, socio-demographic, clinical history was collected. Epworth Sleepiness Scale (ESS), Athens Insomnia Scale (AIS), Pitsuburg Sleep Quality Index (PSQI) scores were measured for assessment of daytime sleepiness, insomnia symptoms and sleep quality respectively.  

Results: Median Vitamin B12 was 342 (266, 446) pg/mL. Excessive daytime sleepiness (ESS>10) was reported in 27% of the participants, insomnia symptoms (AIS ?6) in 40% and poor sleep quality (PSQI > 5) in 37%. After multiparametric adjustments (for age, gender, obesity, co-morbidities, smoking, marital, educational status), B12 levels [OR (95% CI) 0.99 (0.98?1.0), p=0.04], showed significant independent associations with insomnia symptoms, but not with poor sleep quality [OR 0.99, (95% CI) 0.99-1.0, p=0.22) or sleepiness [OR = 0.99, (95% CI) 0.99-1.0, p=0.017)]. Subgroup analysis within the quartiles of vitamin B12 levels showed that participants with higher vitamin B12 in the third [OR (95% CI) 0.31 (0.13?0.75), p=0.009] and fourth quartiles [OR (95% CI) 0.42 (0.19?0.96), p=0.04] reported lower (better) scores for insomnia after adjustments.

Conclusion: Our results show that higher vitamin B12 were associated with insomnia symptoms. However, further research is needed in order to determine the relationship between sleep and vitamin B12.