21st-century life sets your internal clock out of sync with nature

Chronobiology looks at how light and other factors disturb sleep patterns and take toll on wellbeing and health

In ancient times, people woke at sunrise, slept after sunset and the rhythms of our lives matched those of nature. Today, our constant exposure to artificial light from mobile and computer screens and LEDs has knocked us out of sync with nature and put us at greater risk of chronic mental and physical ill-health.

Indigenous people, who are closer to nature, have, scientists say, a better quality of sleep than those of us who have been increasingly cut off from the signals that nature tries to tell us, such as when to sleep, rest and eat as a consequence of living in an “always on” society. It’s notable that insomnia – linked to several mental disorders – is unknown to the Aboriginal people.

“They still live a life where they are very locked into the sunrise and sunset because they don’t have electricity,” says Prof Andrew Coogan, a behavioural neuroscientist at Maynooth University researching biological rhythms and the area of chronobiology.

“They don’t have phones and Netflix and all those other attractions,” Coogan says. “They live like we probably used to live. They don’t sleep a whole lot longer, about seven hours, but they do sleep well. If they go to bed, then they are asleep.”


Scientists have known since at least the 1960s, notably through the seminal experiments of German physiologist Jochen Aschoff, that people had an internal body clock. His subjects were medical students who were asked to live inside converted second World War bunkers, where they were exposed only to artificial light. “When you put people in this sort of environment, their 24-hour readings kept going,” Coogan adds. “It’s not just us reacting to what is going on outside, we actually have this self-sustaining biological clock inside.”

He is investigating disruption to the biological clock in shift workers, and people with jet lag, where the internal body clock is at odds with their destination. “Our internal clocks are constantly being tweaked to the world in which we live,” Coogan notes, “Our work looks at what happens when the competing demands of 21st-century life is in conflict with our clock.”

We all born either larks, or owls, when it comes to our chronobiology, and some of us function better in the morning and others in the evening. Our rhythms also vary with age, with teenage chronology often at odds with middle-aged parents.

“Anyone with a teenager, or who has been a teenager, will know that teenagers do not naturally tend to get up at 7am in the morning,” says Coogan. “During school time they have to get up at about that time to make the school start. That introduces a tension between the internal biological time and social time outside; we call that social jet lag.”

Teenage jet lag

It is not just teenagers, who can experience social jet lag, says Coogan. “A very simple indicator of whether we have social jet lag or not is if we use an alarm clock to wake up during the workday. When our bodies are forced to wake up before our biological rhythm or the sleep system is ready to wake up.”

Social jet lag, where we are out of sync with our environment and suffering sleep disruption is a serious consequence of modern life, linked with a greater risk of obesity, depression and anxiety. It exacerbates Type 2 diabetes and is also linked to post-traumatic stress disorder (PTSD). When we binge watch Netflix, or constantly scroll through our phones late at night, it delays sleep onset, and contributes to social jet lag, he points out. Interestingly, the pandemic saw it reduced as people commuted less and spent more time in bed.

Light pollution is also increasing and also disrupting our biological rhythms. “The old yellow sodium bulbs and streetlights are being replaced by LED lights, which are more energy efficient, but a lot brighter,” says Coogan. Birds see this bright light at night and thinking it’s daytime. This is messing with their biology, and we suspect it’s also a problem for people as well.”

About 20 per cent of the adult working population in Ireland engages in at least some shift work, despite the fact that the World Health Organisation has classified it as a probable carcinogen. “Shift work obviously screws with your body clock because we are completely working against our clocks,” says Coogan. “It is associated with increased risk of hormonal-dependent cancers, because hormonal systems are highly driven by the circadian clock.”

“We do a lot of stuff that doesn’t need to be 24/7,” he says. “We don’t need 24-hour call centres. What will happen is that the evidence will get so great about the detrimental effects of shift work that there will be litigation. This already happened in Denmark, where a group of nurses claimed that their breast cancer was an occupational health disease.”

Mental health

It’s not just animals that have an internal clock. The internal clock of many tiny micro-organisms living in our gut plays a big role in maintaining our mental health. John Cryan, UCC professor of anatomy and neuroscience, is an authority on signals that pass between the gut microbiome – the group of microbes that live in the intestine – and the brain, and how it that impacts health.

An area of the brain called the suprachiasmatic nucleus, or SCN, is thought to be the “master clock” regulating how our body responds to the 24-hour cycle. “It is the bridge in the brain that gets signals coming into the visual system,” Cryan adds. “We humans have evolved to have this master clock.”

UCC students were studied at exam time – a time of stress – and given a probiotic (a substance the encourages microbes to grow) to see if it could reduce their stress. It did, Cryan confirms, and it also improved their quality of their sleep. “The take-home message is that the microbes can be playing a key role in regulating the master clock; this might have a knock-on effect in terms of how we deal with stress and mood changes.”

“We’ve known for 40 years that sleep disturbances are a core symptom of bipolar, but we still don’t really know how to do anything about it,” Cryan notes.

Dr Anne Curtis, based at the school of pharmacy and biological sciences at the Royal College of Surgeons in Ireland, has been interested in the link between inflammation and biological rhythms since she started her research career in Prof Luke O’Neill’s lab in Trinity College.

When the biological clock is disrupted, such as occurs with jet lag, Curtis says macrophages – the white blood cells that are one of the immune system’s “first responders” to foreign substances – begin to lose function and start to resemble older cells. “There is an age-related effect and there is more of the production of pro-inflammatory cytokines as well,” she says.

“Another area I’m interested it is how the clock tries to prepare the body for its next meal in a predictable manner,” says Curtis. “We tend to be more insulin-sensitive during the day, when we are likely to have higher glucose levels. This means that the macrophage is primed differently during the day and night.”

Curry chips

The reason why eating curry chips at 2am is bad for you is because it’s negatively impacting your immune cells, “which aren’t supposed to be responding to food at that time”.

“During the day the macrophages are on the alert for danger because you are much more likely to get infected when you are moving around. At night time what your immune cells are trying to do is to strategise for the next day,” Curtis adds – this is akin to an army coming back to HQ after battle.

Curtis says that particular illnesses often flare up more at particular times of the day, and she is interested in exploring how vaccines can be administered at a time that will produce the best effects. “Evidence suggests that mRNA vaccines work better when administered at certain times of the day.”

Animals like horses also have natural biological rhythms which are interrupted by living inside under artificial light indoors – which is also costly to breeders. Barbara Murphy, professor of agriculture and food science at UCD, found a solution. She noted breeders put mares “under lights” in winter to encourage them to go “into foal” earlier the following year. They want foals born in January and the mare going back into foal inside a month. That means a 335-day gestation period – ie the mares are ready to foal again in January the following year.

It cost breeders €1,000 to keep each mare inside under lights each year. Murphy came up with a device that shines light into one eye of the mare, tricks her into foaling early and is worn like blinkers. The light in the eye fools the mare, even in the dark depths of winter, into thinking it’s time to go into foal. This led to the setting-up of a UCD on-campus company, Equilume, in 2013.

“It’s like a little racing blinker that you would see a horse wearing for racing,” said Barbara. “It has a cup over one eye that has a set of blue LEDs. It has pretty sophisticated electronic circuitry. Once you activate it once, it comes on and stays on until 11pm and repeats that cycle.”

Whether it’s horses, micro-organisms or people, all living things are ruled by an internal clock. This is increasingly out of sync with nature, and ticking towards an uncertain and probably unhealthy future.