Light & Lighting: Medical & Health Effects


I knew the job was dangerous when I took it ...
Jul 19, 2004
Out of Bounds
I couldn't locate a thread focused on the medical / health effects of light or lighting, so I'm starting one ...
Night-Time Exposure to Blue Light – Including Many Tablet and Phone Screens – Associated With Increased Risk of Cancer

Blue light has become an increasingly common component of urban outdoor lighting. But how does it impact our health? A team led by the Barcelona Institute for Global Health (ISGlobal), a center supported by the “la Caixa” Foundation, has conducted the first study of the association between night-time exposure to outdoor artificial light and colorectal cancer. The findings, published in Epidemiology, show that exposure to the blue light spectrum may increase the risk of this type of cancer.

Previous studies have found associations between night-time exposure to artificial light — especially blue light — and various adverse health effects, including sleep disorders, obesity and increased risk of various types of cancer, especially in night-shift workers. Blue light is a range of the visible light spectrum emitted by most white LEDs and many tablet and phone screens. An earlier study by ISGlobal found a link between exposure to blue light at night and increased risk of breast and prostate cancer.

“Using the same methodology as the previous study, we decided to analyze the relationship between exposure to artificial light and colorectal cancer, the third most common type of cancer worldwide after lung and breast cancer,” explained Manolis Kogevinas, Scientific Director of the Severo Ochoa Distinction at ISGlobal and coordinator of the new study. The World Health Organisation’s International Agency for Research on Cancer (IARC) classifies night-shift work as probably carcinogenic to humans; breast, prostate, and colorectal cancer are associated with the highest risk. ...

This 2018 study indicated light pollution is correlated with insomnia and sleeping pill usage in older people.
First-of-Its-Kind Study Reveals a Shockingly Obvious Reason For Insomnia

Many adults suffer from insomnia, often without any obvious reason why they struggle to fall or stay asleep.

But a first-ever population level study has just given us a big clue.

Scientists have reported a significant link between insomnia in older adults and the levels of light pollution in an area – suggesting there's a relationship between artificial light and how easily we can sleep soundly in our later years. ...

And this study isn't alone in linking light pollution with health issues. While artificial light has no doubt helped us as a civilisation, we're now seeing more evidence of the damage it can do too – it's even been linked with higher breast cancer rates.

We also know that light can cause disruption in our circadian rhythm – that built-in biological clock that helps us know when it's time for some serious rest. Staring at smartphones is thought to be one way light interferes with the body's rest patterns. ...

This 2021 study indicates moonlight affects sleep patterns during the part of the month when there's more moonlight earlier in the evening.
The Full Moon Changes How People Sleep Without Us Ever Realising, Says Study

In modern times, a great deal of research has focused on the way that artificial light sources mess up our sleep and health, due to the unnatural effects of illumination after the Sun goes down.

But just how unnatural is night-time light anyway? After all, humans have always been exposed to variable levels of light at night, due to reflections of sunlight from the waxing and waning Moon – and this shifting radiance stimulates us in ways we aren't fully aware of, new research suggests.

"Moonlight is so bright to the human eye that it is entirely reasonable to imagine that, in the absence of other sources of light, this source of nocturnal light could have had a role in modulating human nocturnal activity and sleep," a team of researchers, led by senior author and neurobiologist Horacio de la Iglesia from the University of Washington, explain in a new study. ...

Tracking the participants' sleep activity over the lunar month cycle, the researchers found the same kind of pattern could be seen in their sleep and waking, regardless of where the volunteers lived.

"We see a clear lunar modulation of sleep, with sleep decreasing and a later onset of sleep in the days preceding a full Moon," de la Iglesia says.

"Although the effect is more robust in communities without access to electricity, the effect is present in communities with electricity ... "

As for what gives rise to these effects, the researchers contend that extended nocturnal activity stimulated by moonlight could be an evolutionary adaptation carried over from the time of pre-industrial human societies – with the ability to stay up and do more under a brilliant full Moon benefitting all kinds of traditional customs still enjoyed by peoples without electricity today. ...

"Although the true adaptive value of human activity during moonlit nights remains to be determined, our data seem to show that humans – in a variety of environments – are more active and sleep less when moonlight is available during the early hours of the night," the researchers explain. ...

This study suggests daily exposure to bright natural light during the day has beneficial effects on mood, sleeping, and reducing risk for depression.
Large-Scale Study Reveals The True Health Benefits of Getting Outdoors More

Getting a daily fix of sunshine could boost your general health, with new research linking time spent outside with better mood, improved sleep and a lower lifetime risk of depression.

"Getting bright light in the day is as important as avoiding light at night," says psychologist and sleep researcher Sean Cain of Monash University in Melbourne, Australia, whose previous experimental studies have shown how artificial light impacts sleep and circadian rhythms. ...

Past research has shown that spending time outdoors and in nature has a host of health benefits, part of which might be related to natural light being the most important environmental time cue for the body's circadian rhythms.

Not getting enough of natural light could be a key factor contributing to low mood and sleep troubles which are also associated with depression, a common mood disorder and one of the leading causes of disability worldwide. ...
Light can affect your body even when you sleep. Even small amounts of ambient light can cause negative somatic effects while you sleep.
Even Moderate Ambient Light During Sleep Is Harmful – Increases Risk for Heart Disease and Diabetes

Close the blinds, draw the curtains and turn off all the lights before bed. Exposure to even moderate ambient lighting during nighttime sleep, compared to sleeping in a dimly lit room, harms your cardiovascular function during sleep and increases your insulin resistance the following morning, reports a new Northwestern Medicine study.

“The results from this study demonstrate that just a single night of exposure to moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, diabetes, and metabolic syndrome,” said senior study author Dr. Phyllis Zee ... “It’s important for people to avoid or minimize the amount of light exposure during sleep.”

There is already evidence that light exposure during daytime increases heart rate via activation of the sympathetic nervous system, which kicks your heart into high gear and heightens alertness ...

“Our results indicate that a similar effect is also present when exposure to light occurs during nighttime sleep,” Zee said. ...

Turkish researchers' results, presented at a recent conference, suggest the notable upsurge in early onset female puberty during the COVID pandemic may not be linked to the disease directly. Instead, it may be linked to the increase in blue light exposure from young girls spending hours online during lockdowns and isolation at home.
Early Puberty in Girls Surged in The Pandemic, And We May Finally Know Why

Among the laundry list of health problems COVID has inflicted on the world's population, one of the more perplexing could be an increase in the number of girls experiencing what is known as idiopathic precocious puberty – abnormally early onset of puberty.

More than one study has spotted the spike in numbers during the early months of the pandemic of what is typically a rare condition, highlighting a potential link between the virus and a trigger for early adolescence.

Now a study presented at the 60th Annual European Society for Paediatric Endocrinology Meeting in Rome suggests it might not have anything to do with the infection at all.

Rather the time spent during lockdowns scrolling through smart devices for hours on end could be to blame.

Researchers from Gazi University and Ankara City Hospital in Turkey exposed 18 immature female rats to a spectrum of light predominantly emitted by our LED screens for relatively short or long periods each day, finding those bathed in the blue-tinged light for longer bouts showed the hallmarks of maturity sooner than the rest.

"We have found that blue light exposure, sufficient to alter melatonin levels, is also able to alter reproductive hormone levels and cause earlier puberty onset in our rat model. In addition, the longer the exposure, the earlier the onset," says endocrinologist and lead author Aylin Kilinç Uğurlu from Gazi University.

Though far from a slam-dunk on the case of why more girls around the world might have hit puberty when they did during the pandemic, it's a finding that should be taken seriously as we become increasingly reliant on personalized digital technology. ...