Who hasn’t heard about the ravages of night shift work? Countless studies document a whole array of physiological effects ranging from the gastrointestinal tract  (irregularity) to cardiac (increase in the incidence of hypertension, irregular heartbeat, myocardial infarction, and stroke) to metabolic (increased craving for carbohydrates and high calorie foods) to increased susceptibility to infection because of reduction in the immune response. And let’s not forget the psychological effects: irritability, reduced capacity to focus, increased drug use, reduced reasoning and impaired judgment, increase in the rate of depression and suicide.

These effects are not limited to night shift work. Adolescents tend to stay up late and get less than 7-8 hours of sleep at night. Their minds are sluggish in the morning and go downhill from there. Many simply fall asleep in class. In fact, inadequate sleep has been documented in the society at large.

Or what about jet lag? Who hasn’t experienced the mental fog after a long flight crossing several time zones? Road warriors brag about doing business after a long trip and a couple of hours of sleep. Has anybody looked at the decision-making capacity of their coffee-addled foggy brains? It would be a wonderful study to perform and could be enormously useful to business.

The total cost of biological clock disruption to society must be massive.  If there is a study that attempted to quantify it –I am not aware of it.

We are not alone

Remember the scene from Romeo and Juliet (act 3, scene 5)?

“Wilt thou be gone? it is not yet near day:
It was the nightingale and not the lark,
That pierced the fearful hollow of thine ear;
Nightly she sings on yon pomegranate-tree:
Believe me, love, it was the nightingale.”

I am always reminded of it whenever an American Robin in our neighborhood starts singing his heart out around midnight. Poor guy, he is supposed to sing at dawn; he got totally screwed up, or more specifically, his biological clock got out of whack. But why? It was a mystery to me until I came across an article published today in Current Biology titled “Artificial Night Lighting Affects Dawn Song, Extra-pair Siring, and Lay Date in Songbirds.”

The researchers, from the Max-Planck Institute of Ornithology in Germany investigated effects of artificial night lighting on dawn song in five common forest-breeding songbirds. In four species, males near street lights started singing significantly earlier at dawn than males elsewhere in the forest, and this effect was stronger in naturally earlier-singing species. Just an amusing anecdote? The implications are far more interesting.

Females of these species (and many other species, including primates) like to have extra-marital liaisons early in the morning. First, it must be a lot of more fun even for the birds. Second, it increases their chances of mating with the choice males, because the early risers are more fit; “The early bird gets the worm”, as the saying goes. Well, the young yearlings yearn to get a female, any female. But the older, more mature and fitter males always get there first. But with anthropogenic (human-generated) light, more of them wake up early and have a better chance at getting to the female first. Indeed, the study shows that in birds living in areas with street lights the yearling rate of success in getting to mate early in the morning is double that of yearling in the forest. Hooray! Except that the original intent of these early morning trysts was to ensure that only the fittest get to mate. Now the wimpy young ones who can barely perform a credible job (evolutionarily speaking, of course) get to mate and have offspring.  And this, of course, results in the gradual degradation of the fitness of the population. What a profound consequence of seemingly inconsequential street light. By the way, in case you wondered, “Lay Date” in the title of the article has nothing to do with what you think; it means that the date of egg-laying is earlier as a consequence of these early morning trysts.

Moral of the story: the biological clock is deeply embedded in our genome, hard-wired in our brain, all important to our physiology and well-being. We mess with it at our own peril.

Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.