Over recent years, it has become clear that exposure to light during the night can have a negative impact on health.

Now, a new study released today finds that these negative consequences may even be passed on to our children.

Modern society is bathed in light; a far cry from our evolutionary beginnings in the darkness of the African night.

Today, we rarely move more than 1 or 2 meters from a glowing screen.

Researchers are slowly untangling the effect that this might be having on our minds and bodies.

Studies have shown that dim light exposure during naturally dark hours is linked to various health problems, including some cancers and diabetes. So, should we ditch our computers, televisions, and cell phones after dark?

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Building on past research

The new study, published in Scientific Reports, concludes that exposure to light at nighttime might not just affect us – it might impact our future children’s health, too.

The new findings come from The Ohio State University.

The researchers knew from earlier studies that stressors could cause hormone disruptions in adult mice, altering their physiology and behaviour.

They also knew from their own previous research that animals exposed to light during dark hours showed a reduction in their immune response.

Similarly, they also found that, by disrupting circadian rhythms – which are daily sleep/wake cycles – dim light at night increased the body weight of mice.

The scientists – led by Yasmine Cisse, a graduate student, and Randy Nelson, professor and chair of neuroscience at Ohio State’s Wexner Medical Center – set out to build on these earlier results.

They designed a study to investigate whether parents could pass these deficits on to their offspring via epigenetic changes.

Epigenetics describe genetic changes other than alterations in the actual sequence of the DNA; they are changes in the way that genes are expressed.

For instance, some lifestyle choices, such as smoking, can cause certain sections of DNA to be switched on or off. These changes can then be passed to offspring while maintaining the exact same genetic code.

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The impact of nocturnal light

Investigating how nocturnal light interferes with general health is a difficult task because disturbed sleep can have a negative impact on health, separate from the effects of light exposure at night.

It is necessary to tease apart the effects of nocturnal illumination and sleep disturbance.

To tackle this problem, the team chose to use Siberian hamsters, a naturally nocturnal animal. In this way, they could measure the impact of light exposure during the night without directly affecting their sleep quality.

The team exposed the hamsters (male and female) to two lighting regimes for nine weeks: either a standard light day and dark night cycle, or dim light during the night.

The hamsters were then allowed to mate before being returned to standard light conditions. The next generation of hamsters were all raised in standard light conditions.

Upon examination, the researchers found that the offspring of parents exposed to a dim light at night did indeed have measurable immune and endocrine impairments.

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The importance of light pollution

It appeared that both mothers and fathers independently passed these deficits on to their offspring.

This is important, as Nelson explains: “These weren’t problems that developed in utero. They came from the sperm and the egg. It’s much more common to see epigenetic effects from the mothers, but we saw changes passed on from the fathers as well.”

Cisse says: “This suggests that circadian disruptions can have long-ranging effects in offspring and that’s concerning.”

Specifically, the hamsters whose parents had been exposed to light at night displayed a reduction in immune response when faced with a foreign substance.

They also noticed changes in the genetic activity of the spleen: hormone receptors for melatonin and glucocorticoids were reduced in number.

That such a simple intervention could cause a significant response was quite surprising to the researchers. As the authors note: “These data demonstrate that a seemingly innocuous stimulus – dim light exposure at night – is sufficient to induce transgenerational effects on physiology.”

Nelson believes that “people are beginning to accept that light pollution is serious pollution and it has health consequences that are pretty pronounced – an increase in cancers, depression, cardiovascular disease, diabetes, and anxiety disorders.”

These findings will need to be replicated in humans, but the message is that the technology that we are surrounded by may be negatively impacting our body’s ability to fight disease.