Night Light Linked to Cancer Risk, With Astronauts' Help

Kristin Jenkins

May 03, 2018

The first study to use nighttime photos of Earth taken by astronauts on the International Space Station found that exposure to high levels of outdoor artificial light at night (ALAN) in the blue spectrum was associated with an increased risk for two cancers.

The findings are from an observational study and therefore are not definitive.

Investigators evaluated exposure to ALAN among individuals who had never worked at night and who were part of a population-based, case-control study known as MCC-Spain.

For the study, the team enrolled 1219 breast cancer patients, 1385 women who did not have cancer to serve as control participants, 623 prostate cancer patients, and 879 men who did not have cancer to serve as control persons from 11 regions in Spain from 2008 to 2013.

The investigators determined exposure to indoor ALAN using questionnaires. Outdoor ALAN exposure was analyzed using images from the International Space Station that were available for Barcelona and Madrid for the period 2012-2013. The analysis included "geocoded" data for each participant's longest place of residence. These data allowed the investigators to determine how much night light, including light in the blue spectrum, there was in each participant's neighborhood.

Light in the blue spectrum is attracting scientists' attention because it is increasingly being used in light-emitting diode technology in urban settings, say the study authors, led by Manolis Kogevinas, MD, PhD, of the Barcelona Institute for Global Health, Spain. The new study was published online April 23 in Environmental Health Perspectives.

The team reports that exposure to outdoor ALAN in the blue spectrum was associated with breast cancer (adjusted odds ratio [OR] for highest vs lowest tertile, OR = 1:47) and prostate cancer (OR = 2:05).

Not all study data indicate that any and all light exposure was harmful.

For example, those exposed to the highest intensity vs the lowest intensity of outdoor ALAN in the visible spectrum were more likely to be control persons than cancer patients, particularly prostate cancer patients.

Men who slept in "quite illuminated" bedrooms were at higher risk for prostate cancer (OR = 2:79) than with those who reported sleeping in total darkness. By contrast, women in "quite illuminated" bedrooms were at slightly lower risk for breast cancer (OR = 0:77).

"Although both cancers were less likely among those in the highest versus lowest tertile of exposure to outdoor ALAN in the visible spectrum, outdoor ALAN in the blue-light spectrum, which is believed to be the most biologically relevant exposure, was positively associated with prostate cancer and, to a lesser extent, with breast cancer," the investigators write.

"Exposure to ALAN is ubiquitous and whether the spread of exposure to ALAN may increase cancer risk and how this could be prevented are public health issues," they add.

"This is where the rubber meets the road," said Richard G. Stevens, PhD, professor of cancer epidemiology at the University of Connecticut Health Center in Farmington, who was was asked for comment. "This is a huge public health problem."

This study "adds to a growing body of evidence about lighting and risk of breast cancer," Stevens said. It also points to nighttime light pollution as "an important environmental issue, as big as poisoning of the water and air," he told Medscape Medical News. "This is the tipping point," he added.

In the study, estimates of exposure to indoor ALAN in the full light spectrum (as opposed to the more limited blue light spectrum), using participant questionnaires and face-to-face interviews, demonstrated an association with an increased risk for prostate cancer but not with an increased breast cancer risk, the investigators say.

Prostate cancer was positively associated with the highest level of indoor illumination in the full light spectrum during bedtime compared with no indoor illumination (OR = 1.80).

Conversely, there was no evidence of an association between indoor ALAN in the full light spectrum and increased risk for breast cancer (OR = 0.94).

This is also the first time that the spectrum of emissions from nighttime lighting has been measured, the researchers note. Prior studies have relied on data from "color-blind" satellite images that detected light but did not measure the spectrum of emissions from nighttime lighting.

Previously, Kogevinas and colleagues demonstrated an overall higher risk for breast and prostate cancer in night shift workers who were exposed to high levels of indoor ALAN from a study population of 4106 participants. For the current analysis, they enrolled persons who had never worked the night shift.

A parallel evaluation of chronotype using the Munich Chronotype Questionnaire provided no clear evidence that being a "morning" vs an "evening" person modified any association between ALAN and prostate or breast cancer. This finding is consistent with their previous study in night shift workers, the authors say.

Clinicians should consider evening and nighttime lighting in patients' homes when assessing health, advised Stevens. Lightbulbs that are relatively dimmer and that emit light of longer wavelength are best, he said. He noted that in his own bathroom, he uses a nighttime plug-in with a dim red light.

"We don't have to go back to living in a cave, but we do need to transition to nighttime physiology," he said. "This is very clear now."

We don't have to go back to living in a cave, but we do need to transition to nighttime physiology. Dr Richard Stevens

In the absence of electric light, the body "gets ready for bed" by increasing the propensity to sleep after sunset. Melatonin levels rise gradually, the metabolism slows, and levels of leptin increase, dulling hunger. In today's fast-paced world, however, many are exposed to too much bright light and to light in the blue spectrum at night. This prevents the transition to nighttime physiology, Stevens said. "That can't be good," he summarized.

Stevens noted that studies of sleep duration in indigenous cultures in South America and Africa show that preindustrial societies do not sleep longer than modern societies. In fact, they average 6.9 to 8.5 hours per night. However, they do tend to fall asleep 3.3 hours after sunset and often awaken just before dawn.

The study authors point out that light emitted by portable electronic devices with self-luminous displays and energy-efficient lighting may contribute to indoor ALAN exposures. "The use of such devices is increasing and has a significant effect on decreasing melatonin production if they are used before bedtime," they say.

This study was funded by the AccionTransversal del Cancer, the Instituto de Salud Carlos III-FEDER, the Fundació n Marqu é s de Valdecilla , the ICGC International Cancer Genome Consortium CLL, the Junta de Castilla y León, the Consejería de Salud of the Junta de Andalucía, the Conselleria de Sanitat of the Generalitat Valenciana, the Regional Government of the Basque Country, the Consejerí a de Sanidad de la Regi ón de Murcia, the European Commission, the Spanish Association Against Cancer (AECC) Scientific Foundation,the Catalan Government-Agency for Management of University and Research Grants (AGAUR), the Fundació n Caja de Ahorros de Asturias, the University of Oviedo, the STARS4ALL project, and the ORISON project, and by the Cities at Night project. The study authors and Dr Stevens have disclosed no relevant financial relationships.

Environ Health Perspect. Published online April 23, 2018. Full text

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