[This article originally appeared in Catalan in Espai Salut, a bulletin published by the Diputació de Barcelona]
Midwinter is the time of year with the fewest daylight hours and the greatest exposure to artificial light. Throughout the evolution of our species, humans lived with stable and regular cycles of light and darkness until the beginning of the 20th century. At that time, the pattern started to change, first with the advent of widespread artificial lighting at night and, more recently, due to our increased exposure to white light emitting diode (LED) light—used outdoors to illuminate streets, monuments, etc. and inside our houses to illuminate the screens of our electronic devices (tablets, mobile phones, and so on).
There is no question that artificial light opened the door to immense progress, allowing us to extend our daily activity into the night hours. Nevertheless, the indiscriminate use of artificial light has a number of other impacts, some with negative effects on human health. In particular, exposure to LED light with a blue peak in its emission spectrum may have a harmful effect on our health because the blue light suppresses the production of melatonin, a hormone the body starts to produce naturally in the afternoon, reaching maximum levels during the hours of darkness.
Exposure to LED light with a blue peak in its emission spectrum may have a harmful effect on our health because the blue light suppresses the production of melatonin
One of the functions of melatonin is to synchronize our biological clock and cue the light-dark cycle. This prepares our body for sleep, triggering a series of physiological responses that regulate various bodily functions at night, including temperature, blood pressure, the secretion of digestive enzymes, and hormone production.
In addition to synchronizing circadian rhythm—the internal clock that guides our biological rhythms—melatonin also has antitumor, neuroprotective, immune modulatory, anti-inflammatory and antioxidant effects. Consequently, inhibition of melatonin synthesis can cause health problems. In fact, in 2007, the International Agency for Research on Cancer (IARC), which forms part of the World Health Organisation (WHO), classified shift work that disrupts the circadian rhythm as a probable carcinogen.
Numerous studies have evaluated the health effects of exposure to artificial light at night, in both experimental animals and humans. Particularly in the case of shift workers, researchers have observed associations with conditions such as diabetes, obesity and heart disease as well as an increased risk of hormone-dependent malignancies like breast and prostate cancer (Schernhammer et al., 2001; Papantoniou et al., 2015).
The International Agency for Research on Cancer (IARC) classified shift work that disrupts the circadian rhythm as a probable carcinogen
There is less scientific evidence available on the effects on the general population of night time exposure to street and indoor lighting, but the findings published to date all point in the same direction.
For example, a recent study in Barcelona and Madrid led by ISGlobal (Garcia-Saenz et al., 2018) found an association between exposure to higher levels of artificial blue light and an increased risk of breast and prostate cancer. The data on artificial light exposure in this study was extrapolated from night time images taken by astronauts on NASA’s International Space Station (ISS).
Barcelona. Image courtesy of the Earth Science and Remote Sensing Unit, NASA Johnson Space Center. http://eol.jsc.nasa.gov
A recent study in Barcelona and Madrid led by ISGlobal found an association between exposure to higher levels of artificial blue light and an increased risk of breast and prostate cancer
Various authors have studied exposure to light emitted by electronic devices during the three-hour period just before sleep (Chang et al., 2014; Akacem et al., 2017). Their results indicate a marked reduction in melatonin levels and quality of sleep in addition to decreased intellectual performance the next day.
It is also interesting to note the importance of exposure to light during the day, ideally from the sun rather than from artificial blue light sources. Such exposure synchronizes our biological clocks, signalling to the body that it is time to be awake and active. Conversely, when darkness falls, the most appropriate kind of illumination is a warm or orange light, which has less effect on melatonin production. We can use screen filters on our electronic devices to obtain this kind of orange light. Today, many cities around the world have chosen to switch to LED street lights, which emit warmer colours with little or no blue component. In this way, they can reduce the light pollution that invades homes while we sleep as well as direct exposure to blue light after nightfall during the hours we spend on the street before going home.
When darkness falls, the most appropriate kind of illumination is a warm or orange light, which has less effect on melatonin production
While the available scientific evidence is still inconclusive, the question of the health effects of LED lighting needs further investigation and, pending more information, great care should be taken.