Against the grain

We humans are diurnal animals, as much as bats are nocturnal. Our eyesight is good, but our hearing and sense of smell are weak — the dark is a dangerous place for us. Fear of the dark, so common among children, is likely a primal memory of our kind’s vulnerability at night, living among hungry creatures that are better suited to being active after the sun goes down.

Hospital workers, police and bakers are needed at night to serve their special functions. And in the 24/7 world of 21st-century commerce, much work goes on around the clock. The customers demand it. The bosses demand it. The shareholders demand it. Costly equipment and buildings give the best return when kept constantly employed, and as long as the human element is still needed, workers must be found to go against the grain of custom and biology and work the night shift.

The body has its ways, however, and they do not necessarily yield to the requirements of business. The production of melatonin, the division of cells, the secretion of hormones and the repair of damaged DNA, among other bodily functions, do not take place steadily, but fluctuate in the course of 24 hours. Life on earth evolved with a 24-hour rotation of the planet, and even prokaryotic organisms carry a molecular clock keyed to that day length. The human circadian rhythm, however, is slightly off kilter — running slightly over 24 hours when experimental subjects are denied access to time cues. To keep in synch, our internal clock must be reset by those cues, particularly daylight.

Most sleep experts say adjusting fully to being active at night and asleep during the day is not entirely possible, and night shift work is correlated with certain cancers and with depression and other mental illness, as well as with sleep disorders. Most Americans are now sleep-deprived, but night workers are more so, by an hour and a half on average, as they are often unable to sleep more than a few hours at a time when they are off duty. That sleep deprivation piles up over the course of a string of night shifts, with increasing cumulative effect on mood, attention and stress level. Some people are better able to cope with an upside-down schedule than others. And some people prefer to work at night, citing the typically lower level of supervision and formality. But for most people, the night shift is a struggle against their nature, a bargain made with necessity. The hours of the day are not alike and interchangable; night, research suggests, cannot be traded with day without a cost.