New Under the Sun:
Volume 7, Issue 1
Letís get real. Humans are higher primates (anthropoids). The only higher primate active at night is the Aotus or owl monkey of South America. The other 200+ species of anthropoids are active during the day. This should be a pretty strong hint that humans are also adapted to be active during the day and to sleep during the night hours. After all, how much do you think we have in common with a 3 pound monkey that spends its entire life in the forest canopy? When we choose to ignore our biological adaptations, we should not be surprised if there are negative consequences to our health.
In the tropics, the sun rises at about 6 am and sets at about 6 pm. There is no variation between summer and winter in this cycle. This is not the case for the temperate zones where the sun may rise around 6 am during the summer and set at 9 pm, but rise at 8 am during the winter and set at 4 pm. Nevertheless, it is in the tropics that humans have their origins, and a tropical lifestyle to which humans are originally adapted. To understand sleep we must examine the impact the day/night cycle had on our hominid ancestors.
Our Ancestors and Sleep
Although our earliest adult ancestors were fairly large and could accurately throw stones as weapons, they were still vulnerable to large predators, particularly cats who hunt at night. There is no evidence of use of fire prior to about one million years ago; and the evidence for controlled use of fire dates to about 500,000 years ago. For our ancestors, particularly the vulnerable young, night was a time of potential danger best met by finding a secure place to sleep and going to sleep soon after sunset. When the sun rose again in the morning, it was time to begin a new dayís activities. Prior to 500,000 years ago, our ancestors probably slept for ten to eleven hours each night. Once they were able to create fire at will, humans would have been able to extend some activities into the night time hours. However, the main benefits of controlled use of fire were: to cook foods; to stay warmer on chilly nights; and to ward off predators while sleeping out in the open. These benefits allowed our ancestors to move into environments that previously had been closed to them. Although campfires may have permitted our ancestors to extend their activities, it is probable that most still slept around ten hours each night simply because their active lifestyle would have resulted in them being too tired to remain awake longer.
Once humans had the ability to control fire, they began to move into the temperate zones. In the temperate zones, the day is longer in the summer and shorter in the winter than is the case in tropical zones. The longer summer days meant that our ancestors probably slept less in the summer, but may have slept more in the winter. It is possible that during the summer, our ancestors in the temperate zones slept for only eight hours each night, but closer to eleven hours each night during the winter months.
This pattern would have changed very little for most individuals until quite recently. Those who managed to stay up far into the night with the aid of artificial light sources probably slept far into the day to make up for this. We can conclude, based on archaeological evidence and the study of less technologically advanced groups, that humans are adapted to and need between eight and ten hours of sleep each night. Unfortunately, our modern 24/7 culture plays havoc with our sleep needs, adversely affecting our mental and physical health and well-being.
The 24/7 Culture and Sleep
In our fast-paced culture where working more than 40 hours per week is considered the norm by many, it may appear that an easy way to gain more time for additional activities is by cutting back on hours slept. This, in fact, seems to be what we are doing. In 1910, Americans averaged nine hours of sleep. But today, around seven hours of sleep is the norm. This reduction in hours slept is true not only of adults, but of children and teens whose growing bodies require ten to twelve hours of sleep each night.
During sleep, our bodies not only rest, but actually build, rebuild, and maintain themselves. When we shortchange our sleep, we short circuit these maintenance activities with detrimental effects to our health. Research has found that a peptide in the stomach (that prevents ulcerations by protecting the cells lining the stomach) is at peak production during sleep, but at very low levels while eating. Sleep deprivation may lead to ulcers and other stomach problems due to inadequate production of effective levels of this peptide.
The immune system functions best in a well-rested body. Those who continue to press forward on their work schedule despite an illness may be pressing forward to death. The death in 1990 of Jim Henson, of Muppet fame, due to an untreated bacterial infection, should be a cautionary tale to all those who think they cannot take the time from work to rest and regain their health. Even the loss of sleep of one hour per night for a week can weaken the immune system to the point where a cold virus can take hold. The best cure for a cold is plenty of rest. So, one way or another, the body will strive to get the rest and sleep it demands. During the lighter sleep stages, particularly during REM sleep, there is an increase in the circulating levels of interleukin-6, part of the immune system. Inadequate sleep of this type (which is associated with dreaming) disrupts the effectiveness of the immune system.
Cancer prevention appears to be associated with adequate levels of sleep in a darkened room. Research shows that melatonin, a hormone produced by the pineal gland during sleep, suppresses tumor growth. Since the pineal gland is affected by light, individuals who stay up into the night under artificial light have reduced production of melatonin. Research comparing breast cancer risk among sighted and visually-impaired women found that those with visual impairments, who would be less affected by ambient light, had a significantly lower risk of developing breast cancer compared to normally-sighted women. Melatoninís tumor-suppressant effects have been examined in breast, prostate, colon, and uterine cancers. It seems probable that melatonin also has a beneficial effect on other cancers. While we sleep, our body heals.
Although everyone needs adequate sleep, it is especially important for children and teens. Learning is enhanced when you have adequate sleep. A study done on cats found that those who were allowed six hours of sleep after a learning challenge had twice the brain development as did those who continued to be exposed to that challenge for an additional six hours. Sleep evidently provides the brain with the time it needs to firmly embed learning and experiences into usable memory. For teens and young adults, pulling all-nighters and cramming for exams are probably counter productive efforts since the information does not have a chance to become embedded in brain circuitry and can vanish into the ether when the student is confronted with a blank test page. Students who are not well-rested not only do poorly on exams, they are less able to concentrate during class, are more disruptive, and are more prone to illness. If parents really desire educational success for their children, they should make sure that their children and teens get at least ten hours of sleep each night, especially before an exam.
Another action that parents could take to help their teens do well in school is to pressure their school districts to change the start time for high school. While teens do still need at least ten hours of sleep to do well, their body clock is slightly shifted compared to children and adults. This means that they have great difficulty being ready to learn at 7:20 am. Schools that have shifted the start time for high school students to 8:30 or 9:00 am have found that students are more alert, get better grades, and have fewer behavior problems. On the other hand, elementary students are ready to learn at 7:20 am. School districts that simply flip the start times for elementary and high schools have achieved great success at little or no cost. When we persist in ignoring our biological adaptations, it should come as no surprise that problems also persist.
Adult workers lacking sufficient sleep are also more irritable, error-prone, and subject to illness than are their well-rested colleagues. This is particularly true for shift workers who work on cycles that conflict with the individualís internal clock and biological rhythms. An individual who works on a day shift during one two-week period and the night shift the next two-week period does violence to his emotional and physical health primarily through disruptions of the natural sleep cycle. Shift workers older than 40 will find that their health steadily and significantly worsens when compared to those who work only during the day. They are also far more likely to suffer from cardiovascular disease and gastro-intestinal problems due to sleep disturbances. Stress levels are exacerbated by inadequate sleep. Since stress is associated with an increased risk of contracting an infectious illness, we have yet another reason to make sure we obtain adequate hours of sleep. Unfortunately, individuals from the lower socio-economic levels who tend to live with the highest levels of stress also have the most difficulties getting adequate levels of sleep. This is reflected in their poorer overall health profiles. Chronic sleep deprivation could be a factor in type 2 diabetes, hypertension, obesity, and memory loss since sleep deprivation affects insulin response and cortisol secretion.
If you are not sleeping long enough, you are more likely to be in an accident. There is an especially clear association between sleepiness and car accidents. An individual who drives while sleepy can be just as impaired as someone who drives while under the influence of alcohol. A worker who did not have enough hours of sleep the night before, who works an eight hour day, and then goes out to a bar for a few drinks after work could be a double driving threat later that evening. But even without drinking, the tired worker without adequate sleep is more likely to be in an accident than is a well-rested worker.
For most of the 20th century, women averaged a longer life span than men, although the gap has been steadily closing in the last few decades. It has been proposed that part of the reason for the better health of women is that they have stronger immune systems. Research examining the thymus and T-cell production, a component of the immune system, found that women have improved thymic function relative to men and that this better functioning extends longer into old age in women than in men. It is only in the last few decades that women have been participating in the work force in large numbers and have been employed in shift work. These changes in the employment profile of women and the resulting disruption to sleep cycles that occurs with shift work may lead to a further narrowing of the gap between male and female life expectancies as women suffer more from a depleted immune system.
Ben Franklin said it best all those centuries ago: Early to bed and early to rise makes a [person] healthy, wealthy, and wise. If you have the option, jettison the shift work. The extra pay is unlikely to offset the increased costs to your health and well-being. Record your late night TV shows and watch them later. Sleeping and dreaming are better for your health than are Dave and Jay, et al.
While a few individuals may function better at night than during the day, humanity is not a nocturnal species. This means that the vast majority of us function best during the daylight hours after a full nightís sleep. While it may be difficult in our 24/7 culture to find the time for an adequate nightís sleep, if we want to maintain our immune systems at peak efficiency and to provide our children and ourselves with an optimal opportunity for learning, we must find the time to sleep. Letís get real and get our beauty (and brain) sleep.
Next issue: Natural Parenting: Part 1
© 2001-2009 Kathleen E. Fuller, PhD. All rights reserved.