This is the next article in our ‘Light and health’ series, where we look at how light affects our physical and mental health in sometimes surprising ways. Read other articles in the series.

Exposure to light is crucial for our physical and mental health, as this and future articles in the series will show.

But the timing of that light exposure is also crucial. This tells our body to wake up in the morning, when to poo and the time of day to best focus or be alert. When we’re exposed to light also controls our body temperature, blood pressure and even chemical reactions in our body.

But how does our body know when it’s time to do all this? And what’s light got to do with it?

What is the body clock, actually?

One of the key roles of light is to re-set our body clock, also known as the circadian clock. This works like an internal oscillator, similar to an actual clock, ticking away as you read this article.

But rather than ticking you can hear, the body clock is a network of genes and proteins that regulate each other. This network sends signals to organs via hormones and the nervous system. These complex loops of interactions and communications have a rhythm of about 24 hours.

In fact, we don’t have one clock, we have trillions of body clocks throughout the body. The central clock is in the hypothalamus region of the brain, and each cell in every organ has its own. These clocks work in concert to help us adapt to the daily cycle of light and dark, aligning our body’s functions with the time of day.

However, our body clock is not precise and works to a rhythm of about 24 hours (24 hours 30 minutes on average). So every morning, the central clock needs to be reset, signalling the start of a new day. This is why light is so important.

The central clock is directly connected to light-sensing cells in our retinas (the back of the eye). This daily re-setting of the body clock with morning light is essential for ensuring our body works well, in sync with our environment.

In parallel, when we eat food also plays a role in re-setting the body clock, but this time the clock in organs other than the brain, such as the liver, kidneys or the gut.

So it’s easy to see how our daily routines are closely linked with our body clocks. And in turn, our body clocks shape how our body works at set times of the day.

What time of day?

Let’s take a closer look at sleep

The naturally occurring brain hormone melatonin is linked to our central clock and makes us feel sleepy at certain times of day. When it’s light, our body stops making melatonin (its production is inhibited) and we are alert. Closer to bedtime, the hormone is made, then secreted, making us feel drowsy.

Our sleep is also partly controlled by our genes, which are part of our central clock. These genes influence our chronotype – whether we are a “lark” (early riser), “night owl” (late sleeper) or a “dove” (somewhere in between).

But exposure to light at night when we are supposed to be sleeping can have harmful effects. Even dim light from light pollution can impair our heart rate and how we metabolise sugar (glucose), may lead to psychiatric disorders such as depression, anxiety and bipolar disorder, and increases the overall risk of premature death.

The main reason for these harmful effects is that light “at the wrong time” disturbs the body clock, and these effects are more pronounced for “night owls”.

This “misaligned” exposure to light is also connected to the detrimental health effects we often see in people who work night shifts, such as an increased risk of cancer, diabetes and heart disease.

How about the gut?

Digestion also follows a circadian rhythm. Muscles in the colon that help move waste are more active during the day and slow down at night.

The most significant increase in colon movement starts at 6.30am. This is one of the reasons why most people feel the urge to poo in the early morning rather than at night.

The gut’s day-night rhythm is a direct result of the action of the gut’s own clock and the central clock (which synchronises the gut with the rest of the body). It’s also influenced by when we eat.

How about focusing?

Our body clock also helps control our attention and alertness levels by changing how our brain functions at certain times of day. Attention and alertness levels improve in the afternoon and evening but dip during the night and early morning.

Those fluctuations impact performance and can lead to decreased productivity and an increased risk of errors and accidents during the less-alert hours.

So it’s important to perform certain tasks that require our attention at certain times of day. That includes driving. In fact, disruption of the circadian clock at the start of daylight savings – when our body hasn’t had a chance to adapt to the clocks changing – increases the risk of a car accident, particularly in the morning.

What else does our body clock control?

Our body clock influences many other aspects of our biology, including:

• physical performance by controlling the activity of our muscles
• blood pressure by controlling the system of hormones involved in regulating our blood volume and blood vessels
• body temperature by controlling our metabolism and our level of physical activity
• how our body handles drugs and toxins by controlling enzymes involved in how the liver and kidneys eliminate these substances from the body.

Morning light is important

But what does this all mean for us? Exposure to light, especially in the morning, is crucial for synchronising our circadian clock and bodily functions.

As well as setting us up for a good night’s sleep, increased morning light exposure benefits our mental health and reduces the risk of obesity. So boosting our exposure to morning light – for example, by going for a walk, or having breakfast outside – can directly benefit our mental and metabolic health.

However, there are other aspects about which we have less control, including the genes that control our body clock.

Frederic Gachon, Associate Professor, Physiology of Circadian Rhythms, Institute for Molecular Bioscience, The University of Queensland and Benjamin Weger, NHMRC Emerging Leadership Fellow Institute for Molecular Bioscience, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Anorexia nervosa is a severe mental health disorder where people fear weight gain. Those with the disorder have distorted body image and hold rigid beliefs their body is too big. They typically manage this through restricted eating, leading to the serious medical consequences of malnutrition.

Anorexia has one of the highest death rates of any mental illness. Yet there are currently no effective drug treatments and the outcomes of psychotherapy (talk therapy) are poor. So we’re desperately in need of new and improved treatments.

Psilocybin, commonly known as magic mushrooms, is one such novel treatment. But while it shows early promise, you won’t see it used in clinical practice just yet – more research is needed to test if it’s safe and effective.

What does treatment involve?

The treatment involves the patient taking a dose of psilocybin in a safe environment, which is usually a specifically set up clinic. The patient undergoes preparation therapy before the dosing session and integration therapy after.

Psilocybin, extracted from mushrooms, is a psychedelic, which means it can produce altered thinking, sense of time and emotions, and can often result in hallucinations. It also has the potential to shift patients out of their rigid thinking patterns.

Psilocybin is not administered alone but instead with combined structured psychotherapy sessions to help the patient make sense of their experiences and the changes to their thinking. This is an important part of the treatment.

What does the research show?

Research has shown improved effects of psilocybin-assisted psychotherapy after one or two dosing sessions, a couple of weeks apart. Most research to date has targeted depression.

Psilocybin has been found to increase cognitive flexibility – our ability to adjust our thinking patterns according to changing environments or demands. This is one of the ways researchers believe psilocybin might improve symptoms for conditions such as depression and alcohol use disorder, which are marked by rigid thinking styles.

People with anorexia similarly struggle with rigid thinking patterns. So researchers and clinicians have recently turned their attention to anorexia.

In 2023, a small pilot study of ten women with anorexia was published in the journal Nature Medicine. It showed psilocybin-assisted psychotherapy (with 25mg of psilocybin) was safe and acceptable. There were no significant side effects and participants reported having valuable experiences.

Although the trial was not a formal efficacy trial, 40% of the patients did have significant drops in their eating disorder behaviour.

However, the trial only had one dosing session and no long-term follow up, so further research is needed.

A recent animal study using rats examined whether rigid thinking could be improved in rats when given psilocybin. After the psilocybin, rats gained weight and had more flexible thinking (using a reversal learning task).

These positive changes were related to the serotonin neurotransmitter system, which regulates mood, behaviour and satiety (feeling full).

Brain imaging studies in humans show serotonin disturbances in people with anorexia. Psilocybin-assisted psychotherapy is showing promise at modifying the serotonin disturbances and cognitive inflexibility that have been shown to be problematic in anorexia.

Research with animals can provide unique insights into the brain which can sometimes not be investigated in living humans. But animal models can never truly mimic human behaviour and the complex nature of chronic mental health conditions.

What’s next for research?

Further clinical trials in humans are very much needed – and are underway from a research team at the University of Sydney and ours at Swinburne.

Our trial will involve an initial 5mg dose followed by two subsequent doses of 25mg, several weeks apart. An initial low dose aims to help participants prepare for what is likely to be a new and somewhat unpredictable experience.

Our trial will examine the usefulness of providing psychotherapy that directly addresses body image disturbance. We are also investigating if including a family member or close friend in the treatment increases support for their loved one.

Data from other mental health conditions has suggested that not everyone sees benefits, with some people having bad trips and a deterioration in their mental health. So this treatment won’t be for everyone. It’s important to work out who is most likely to respond and under what conditions.

New trials and those underway will be critical in understanding whether psilocybin-assisted psychotherapy is a safe and effective treatment for anorexia, and the optimal conditions to improve the patient’s response. But we are some way off from seeing this treatment in the clinic. One of the big issues being the cost of this intervention and how this will be funded.

Susan Rossell, Director Clinical Trials and Professor Cognitive Neuropsychiatry Centre for Mental Health and Brain Sciences, Swinburne University of Technology and Claire Finkelstein, Clinical Psychologist and PhD candidate, Swinburne University of Technology

This article is republished from The Conversation under a Creative Commons license. Read the original article.