Association between night-shift work and level of melatonin: systematic review and meta-analysis

• Published in: Sleep medicine Vol. 75; pp. 502 - 509
• Main Authors: Wei, Tao, Li, Cancan, Heng, Yuanyuan, Gao, Xiang, Zhang, Guimei, Wang, Huachen, Zhao, Xuan, Meng, Zixiu, Zhang, Yanbo, Hou, Haifeng
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.11.2020
• Subjects: 6-sulfatoxymelatonin (aMT6s); Melatonin; Night-shift work; Night-shift work; Melatonin; 6-sulfatoxymelatonin (aMT6s)
• ISSN: 1389-9457; 1878-5506
• DOI: 10.1016/j.sleep.2020.09.018

Night-shift workers are exposed to nocturnal light and are more prone to circadian rhythm disorders. Although night-shift work is thought to be associated with the decrease in melatonin secretion, studies have shown inconsistent results. This systematic review and meta-analysis studied the association between night-shift work and melatonin levels. Pubmed and Embase databases were used for literature searching. The pooled standardized mean differences (SMDs) and 95% confidence intervals (CIs) were used to compare the differences between night-shift workers and the controls. Thirty-three studies reported in 25 articles (1845 night-shift workers and 3414 controls, mean age 45.12 years) were included after a systematic literature review. Data of circulating melatonin levels and its metabolites, 6-sulfatoxymelatonin (aMT6s) in urine were collected for meta-analysis. The results showed that the first morning-void aMT6s level in night-shift workers was significantly lower than in day workers (SMD = −0.101, 95% CI = −0.179 to −0.022, P = 0.012). The level of mean 24-h urinary aMT6s was lower in night-shift workers than day workers (SMD: −0.264, 95% CI: −0.473 to −0.056, P = 0.013). Among fixed night-shift workers, the level of circulating melatonin, as well as first morning-void aMT6s was lower than that of day workers. Our findings indicate that experience of night-shift work is associated with suppression of melatonin production, especially among fixed night-shift workers. •Night-shift work is a highly prevalent experience, introducing nocturnal light and circadian rhythm disorder to the workers.•Our study evidences that night-shift work leads to a decrease in melatonin levels measured by urinary 6-sulfatoxymelatonin.•Preventive measures for reduction of long-term night-shift work may prevent disruption of melatonin synthesis.