When I set out to write my book about insomnia, I asked dozens of insomniacs what they thought had caused their insomnia. Several mentioned constitutional factors.
There are certainly grounds for thinking that a genetic component is involved. People who have a first-degree relative with insomnia are 7 times as likely to suffer insomnia as people without insomnia in the immediate family.
Other people I interviewed attributed their insomnia to stress at work or to family problems. Still others blamed their insomnia on an inability to quiet their mind at night.
The causes of insomnia are still unknown, but many factors can make people more and less vulnerable to it. A prospective study of Norwegian nurses offers new evidence of several factors, some well known and others that have gotten less attention in the past.
Anxiety and Depression
There’s plenty of evidence pointing to a relationship between insomnia and mood disorders. In the nurses’ study, where investigators reviewed data on 799 nurses collected at 2 time points 2 years apart, nurses higher on anxiety and depression measures in 2009 were significantly more likely to report insomnia symptoms in 2011.
The reverse relationship also held for insomnia and anxiety: nurses reporting insomnia in 2009 were more likely to have developed anxiety 2 years later. Surprisingly, although insomnia is widely understood to be a causal factor in depression, the nurses’ study found no evidence of this.
Morningness and Eveningness
The nurses in this study were all shift workers. Other research has suggested that people who dislike getting up early in the morning have an easier time adapting to shift work, where work at night is required.
In the current study, though, the nurses who disliked getting up early in the morning were actually more inclined to develop insomnia than the early risers. Other research has shown that people who like to get up early tend to have better lifestyle regularity and more regular sleep habits. Both these things tend to protect people from developing insomnia.
Some people function quite well despite sleep loss while others feel drowsy and lethargic. (This is largely determined by genetic factors and is thus a stable trait.) Languidity—the tendency to experience drowsiness and lethargy after losing sleep—was found in the nurses’ study to predict an increase in insomnia symptoms over the 2-year period. No surprises here. Impairments in daytime functioning are classic symptoms of insomnia.
Another personality trait—flexibility, or the ability to sleep or stay awake at odd hours—has generally been known to protect against the development of insomnia. Among shift workers, this would be an especially useful trait. But in this study, a high score on flexibility had no positive or negative relationship with insomnia.
Smoking, Drinking, and Caffeine
The overall harmful effects of tobacco, alcohol, and caffeine on sleep are now well known. For many years insomnia was attributed to people drinking too much scotch or too much coffee.
More recently, studies have shown that people with insomnia do not typically drink more alcohol or caffeinated drinks than people who sleep well, and the nurses’ study supports this finding. None of these lifestyle factors predicted an increase in insomnia over time. In fact, nurses reporting insomnia symptoms in 2009 actually reported drinking less caffeine in 2011.
Bullying at Work
Several work-related stressors are known to increase the risk of poor quality sleep, and bullying—persistent exposure to negative actions from others—is one. Day-to-day contact with tyrannical bosses and manipulative supervisors often leads to psychological distress.
Nurses subjected to bullying at work reported more insomnia symptoms over time than the nurses working under better conditions. No surprises here: the worry and stress that result from bullying are two of the leading causes of sleep problems among workers.
Spillover Between Work and Family
Stress in one domain can affect another. In the nurses’ study, negative spillover from work to family and from family to work predicted an increase in insomnia symptoms over time. Conversely, insomnia led to reports of more work-to-family conflicts over time.
Finally, shift work, involving night work and rotating shifts, is known to precipitate insomnia. But in this group of nurses, the association did not hold. This unexpected result might be due to the young age of the nurses (average age 33) and their overall good health compared with shift-working nurses overall, many of whom likely self-selected out of the study.
What factors do you think led to your insomnia?