Reproductive effects of working night and rotating shifts

Recent studies suggest that shift workers who experience exposure to light at night could be at increased risk for adverse reproductive outcomes. Several occupational groups, including health care workers, law enforcement, firefighters, and manufacturing workers are required to work night shifts. Worldwide, millions work at least one night per month. Research will be reviewed on shift work and reproductive outcomes, including menstrual cycle patterns, fertility, pregnancy loss, preterm delivery, and birth weight. Defined by cyclical patterns of circulating hormones, the reproductive system is vulnerable to shifts in circadian rhythms, either through sleep disturbances, altered melatonin production, exposure to light at night, or some other mechanism. The limitations of current research will also be discussed: is there a dose response effect from the number of years of shift work, or can the effects be reversed once shift work stops? Are there different effects from permanent night shift versus rotating shift involving nights? Future research needs will be identified, including the need for validation of self-reported shift work data, the influence of body mass index on the association between shift work and reproductive outcomes, and how working at night changes appetite, diet, and the opportunity for physical exercise. The mechanisms by which shift work affects reproductive health also need to be clarified: lack of sleep, melatonin or other hormone production, and circadian disruption have all been proposed. Recommendations for shift workers will be explored, such as improved sleep hygiene and the importance of weight maintenance through diet and exercise.