May 21, 2026 · 14 min · 10 segments
We’re shining a light on light itself: how natural daylight, vitamin D, and different light spectrums affect your sleep, your mood, your energy, and yes, how quickly you age. Dr Nichola explains the…
Nichola ConlonGuest
Katherine RyanHostNo entities detected.
And this is something that you probably rarely think about, but it actually controls almost every system in your body.
And this is because light is one of the most powerful regulators of your biology, and when it's disrupted, it can really upset your body, and it can accelerate aging in ways that we don't immediately see.
It tells your body what time it is, and that really matters more than most people realize because inside your brain, there is a tiny cluster of cells called the suprachiasmatic nucleus.
Science word of the week
And you don't need to remember that, but just think of it as a master clock, and this clock responds directly to light entering your cells.
So when morning light goes in and it hits your retina, it basically signals to your brain that the day has begun, and that signal is very important because it sets off a cascade in your body to prepare your body and your biology for the day.
So melatonin, which is the sleep hormone, will be switched off, our body temperature will shift, our digestion will prepare, and our focus will sharpen.
And the amazing thing is that this master clock then syncs clocks in almost every other cell of the body because every cell also has its own clock.
Your liver cells have clocks, your gut has a clock, your skin has a clock, and even your immune cells all have clocks.
Now, these cellular clocks then switch thousands of genes on and off across a 24-hour cycle, and this cycle is known as our circadian rhythm.
And research shows that nearly half of all our genes show some sort of circadian variation in activity.
In other words, they are switched on and off every 24 hours according to what the light is doing.
So why is it? Why is it that this light is such an important stimulus? Well, if you think about it, for most of our human history, our ancestors lived in sync with natural light.
They had no shift work, they had no smartphones, and definitely no artificial lights at midnight.
They just had different wavelengths or colors of light that were influencing their biology throughout the day.
For example, blue light throughout the day and in the morning was energizing.
It suppressed melatonin, and it promoted alertness, whereas the warm, red-toned light in the evening from things like the sunset is much more calming.
And this is something that you probably rarely think about, but it actually controls almost every system in your body.
And this is because light is one of the most powerful regulators of your biology, and when it's disrupted, it can really upset your body, and it can accelerate aging in ways that we don't immediately see.
It tells your body what time it is, and that really matters more than most people realize because inside your brain, there is a tiny cluster of cells called the suprachiasmatic nucleus.
Science word of the week
And you don't need to remember that, but just think of it as a master clock, and this clock responds directly to light entering your cells.
So when morning light goes in and it hits your retina, it basically signals to your brain that the day has begun, and that signal is very important because it sets off a cascade in your body to prepare your body and your biology for the day.
So melatonin, which is the sleep hormone, will be switched off, our body temperature will shift, our digestion will prepare, and our focus will sharpen.
And the amazing thing is that this master clock then syncs clocks in almost every other cell of the body because every cell also has its own clock.
Your liver cells have clocks, your gut has a clock, your skin has a clock, and even your immune cells all have clocks.
Now, these cellular clocks then switch thousands of genes on and off across a 24-hour cycle, and this cycle is known as our circadian rhythm.
And research shows that nearly half of all our genes show some sort of circadian variation in activity.
In other words, they are switched on and off every 24 hours according to what the light is doing.
So why is it? Why is it that this light is such an important stimulus? Well, if you think about it, for most of our human history, our ancestors lived in sync with natural light.
They had no shift work, they had no smartphones, and definitely no artificial lights at midnight.
They just had different wavelengths or colors of light that were influencing their biology throughout the day.
For example, blue light throughout the day and in the morning was energizing.
It suppressed melatonin, and it promoted alertness, whereas the warm, red-toned light in the evening from things like the sunset is much more calming.
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