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.

From today, February 3, pregnant women in Australia will be eligible for a free RSV vaccine under the National Immunisation Program.

This vaccine is designed to protect young infants from severe RSV (respiratory syncytial virus). It does so by generating the production of antibodies against RSV in the mother, which then travel across the placenta to the baby.

While the RSV vaccine is a new addition to the National Immunisation Program, it’s one of three vaccines provided free for pregnant women under the program, alongside ones for influenza and whooping cough. Each offers important protection for newborn babies.

The RSV vaccine

RSV is the most common cause of lower respiratory infections (bronchiolitis and pneumonia) in infants. It’s estimated that of every 100 infants born in Australia each year, at least two will be hospitalised with RSV by six months of age.

RSV infection is most common roughly between March and August in the southern hemisphere, but infection can occur year-round, especially in tropical areas.

The vaccine works by conferring passive immunity (from the mother) as opposed to active immunity (the baby’s own immune response). By the time the baby is born, their antibodies are sufficient to protect them during the first months of life when they are most vulnerable to severe RSV disease.

The RSV vaccine registered for use in pregnant women in Australia, Abrysvo, has been used since 2023 in the Americas and Europe. Real-world experience there shows it’s working well.

For example, over the 2024 RSV season in Argentina, it was found to prevent 72.7% of lower respiratory tract infections caused by RSV and requiring hospitalisation in infants aged 0–3 months, and 68% among those aged 0–6 months. This research noted three deaths from RSV, all in infants whose mothers did not receive the RSV vaccine during pregnancy.

This was similar to protection seen in a large multinational clinical trial that compared babies born to mothers who received this RSV vaccine with babies born to mothers who received a placebo. This study found the vaccine prevented 82.4% of severe cases of RSV in infants aged under three months, and 70% under six months, and that the vaccine was safe.

In addition to the maternal vaccine, nirsevimab, a long-acting monoclonal antibody, provides effective protection against severe RSV disease. It’s delivered to the baby by an intramuscular injection, usually in the thigh.

Nirsevimab is recommended for babies born to women who did not receive an RSV vaccine during pregnancy, or who are born within two weeks of their mother having received the shot (most likely if they’re born prematurely). It may also be recommended for babies who are at higher risk of RSV due to a medical condition, even if their mother was vaccinated.

Nirsevimab is not funded under the National Immunisation Program, but is covered under various state and territory-based programs for infants of mothers who fall into the above categories.

But now we have a safe and effective RSV vaccine for pregnancy, all pregnant women should be encouraged to receive it as the first line of prevention. This will maximise the number of babies protected during their first months of life.

Flu and whooping cough

It’s also important pregnant women continue to receive flu and whooping cough vaccines in 2025. Like the RSV vaccine, these protect infants by passing antibodies from mother to baby.

There has been a large whooping cough outbreak in Australia in recent months, including a death of a two-month-old infant in Queensland in November 2024.

The whooping cough vaccine, given in combination with diphtheria and tetanus, prevents more than 90% of whooping cough cases in babies too young to receive their first whooping cough vaccine dose.

Similarly, influenza can be deadly in young babies, and maternal flu vaccination substantially reduces hospital visits associated with influenza for babies under six months. Flu can also be serious for pregnant women, so the vaccine offers important protection for the mother as well.

COVID vaccines are safe in pregnancy, but unless a woman is otherwise eligible, they’re not routinely recommended. You can discuss this with your health-care provider.

When and where can you get vaccinated?

Pregnant women can receive these vaccines during antenatal visits through their GP or in a specialised antenatal clinic.

The flu vaccine is recommended at any time during pregnancy, the whooping cough vaccine from 20 weeks (ideally before 32 weeks), and the RSV vaccine from 28 weeks (before 36 weeks).

It’s safe to receive multiple vaccinations at the same clinic visit.

We know vaccination rates have declined in a variety of groups since the pandemic, and there’s evidence emerging that suggests this trend has occurred in pregnant women too.

A recent preprint (a study yet to be peer-reviewed) found a decrease of nearly ten percentage points in flu vaccine coverage among pregnant women in New South Wales, from 58.8% in 2020 to 49.1% in 2022. The research showed a smaller drop of 1.4 percentage points for whooping cough, from 79% in 2020 to 77.6% in 2022.

It’s important to work to improve vaccination rates during pregnancy to give babies the best protection in their first months of life.

We know pregnant women would like to receive information about new and routine maternal vaccines early in pregnancy. In particular, many pregnant women want to understand how vaccines are tested for safety, and their effectiveness, which was evident during COVID.

GPs and midwives are trusted sources of information on vaccines in pregnancy. There’s also information available online on Sharing Knowledge About Immunisation, a collaboration led by the National Centre for Immunisation Research and Surveillance.

Archana Koirala, Paediatrician and Infectious Diseases Specialist, University of Sydney; Bianca Middleton, Senior Research Fellow, Menzies School of Health Research; Margie Danchin, Professor of Paediatrics and vaccinologist, Royal Childrens Hospital, University of Melbourne and Murdoch Childrens Research Institute (MCRI); Associate Dean International, University of Melbourne, Murdoch Children’s Research Institute; Peter McIntyre, Professor in Women’s and Children’s Health, University of Otago, and Rebecca Doyle, Adjunct Research Fellow, School of Nursing, Midwifery and Social Work, The University of Queensland

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