THE BENEFITS OF SLEEP

The best way to stay in tune with the body’s circadian cycles is to sleep when it is dark outside and wake up with the sun.

Sleeping at night, while it is dark, and being awake during the day, while the sun is up, is an example of a light-related circadian rhythm. High-quality sleep is linked to a multitude of health benefits, including better cognitive function, more efficient metabolism, and a more robust immune system. Conversely, there is increasing evidence that skimping on sleep can increase the risk of many serious diseases and conditions, including cancer, cardiovascular disease, type 2 diabetes, obesity, and dementia.

Most people have experienced how even one night of poor sleep can make them feel bad—and not just tired, but mentally slow and irritable. Sleep rejuvenates the body and mind and helps us be alert, retain information, and think clearly. Sleep is even important for helping regulate our emotions, and there is evidence that sleep-deprived people tend to focus more on negative memories than positive ones.

There are three main categories of compromised sleep: not getting enough sleep; disrupted sleep; and conditions like sleep apnea that affect the quality of sleep. Sleep deprivation is also cumulative and can exact a toll on alertness and performance over time. The body and brain are busy as we slumber. Cellular repair, hormone synthesis, and the consolidation of memories and information all happen while we sleep. Newer research suggests that the continuity and timing of sleep may be as important as the total number of hours spent sleeping.

While we sleep, the body cycles through REM (short for rapid eye movement) and non-REM, or deep sleep. Through the night, the non-REM periods get shorter while the REM periods extend. Physiological changes occur between these stages. For example, breathing rate and blood pressure lower during non-REM sleep and rise during REM sleep. The fluctuations may be critical for maintaining a healthy heart. Consequently, one continuous “sleeping session” might be more beneficial than multiple short periods of sleep for acquiring these benefits.

Also, sleeping when it is dark outside may be just as or even more important than simply getting eight hours of sleep. While this may not be possible for shift workers, there are simple things most people can do to promote higher quality sleep. These include strategies such as limiting screen time, going to bed earlier, and using blackout shades on windows, especially if light pollution is an issue.

SHINING LIGHT ON THE BENEFITS OF DAYLIGHTING

Photo: 22 Waves Creative

Access to fresh air, sunlight, and views of nature has proven health benefits.

In a now-famous study from 1984, researchers found that post-surgical patients recovered more quickly if their rooms included views of green space compared to those whose rooms faced out onto a wall.¹¹

Since then, many studies have focused on the benefits of daylight in health-care settings. In one more recent study of heart attack victims, female patients who were treated in sunny rooms left a day earlier than patients in “dull” rooms.¹²

Studies also show that daylight can affect patients through the circadian system, helping reduce depression and improve sleep patterns. Daylight may also lessen agitation, ease the perception of pain, help night shift workers adjust, and improve the general well-being of staff. As we will see in a later section, artificial lighting is being used to mimic the shifting pattern of light throughout the day, to the benefit of patients.

Even infants benefit from more natural patterns of dark and light. In one study, 41 pre-term infants in critical care units were provided with either constant levels of light or light that cycled from dark and light. Infants exposed to the “cycled” lighting enjoyed greater weight gain; they were also able to feed orally sooner, spent fewer days on the ventilator, and showed better motor coordination.¹³

Daylighting can boost productivity and elevate moods in healthy people too. One large-scale survey of office workers in Sweden showed that mood and vitality were enhanced in healthy people when they were exposed to higher levels of bright daylight.

People spend most of their time at work, and many studies have linked daylighting and views of nature to reduced absenteeism and boosted productivity.¹⁴ In one poll of 1,614 North American employees, respondents named access to natural light and views of the outdoors as the most prized feature of the workplace environment.¹⁵

THE CIRCADIAN SYSTEM AND LIGHT EXPOSURE

Source: Philip Ronan, Gringer/CC BY-SA

Shown here is the electromagnetic spectrum, with a focus on visible light.

Our circadian systems respond to light in several ways. The spectral distribution, or wavelength of the light, the timing and duration of exposure, and a person’s individual lifestyle are all factors. It is important to understand these factors when designing daylighting and artificial lighting.

Light wavelength: The circadian system responds to light differently than the visual system. While the circadian system is most sensitive to short-wavelength (blue) light, the visual system is most sensitive to light in the yellow wavelengths, which are longer.

Timing and duration of exposure: Light in the morning resets our circadian system and synchronizes our circadian rhythm to the local time of the day. On the other hand, light exposure at night can suppress melatonin production and cause us to become more alert, making it harder to go to sleep. Also, while the visual system responds to a light stimulus in a second or less, the circadian system may not respond for several minutes.

A person’s individual history: If a person is exposed to more light during the day, the circadian system is less sensitive to light at night. In other words, more time spent outdoors or in spaces with good daylighting may promote better sleep at night, even in light-polluted spaces.