Why you feel different as the seasons change
Written by BioBlends founder and nutritional biochemist, Dr Libby.
As the daylight hours begin to shorten, something subtle yet powerful starts to shift within. It’s not just that the mornings feel darker or the evenings arrive earlier. Your biology is responding in real time to changes in light exposure – and this influences far more than we might realise.
At the centre of this response is your nervous system, working to interpret light signals and adjust how your body functions across the day. This is where understanding the science can be incredibly empowering. Because when you understand what’s changing, you can support your body in a way that works with it, rather than pushing against it.
Light is more than illumination, it’s information
Every morning, light enters your eyes and travels to a small region in the brain called the hypothalamus. Within it sits your master clock – a cluster of neurons known as the suprachiasmatic nucleus.
This is what regulates your circadian rhythm, your internal 24-hour cycle that influences:
- When you feel awake or sleepy
- How your hormones are released
- Your body temperature
- Your metabolism and energy production
Light is the primary signal that keeps this system in sync, so when light exposure changes, your internal timing shifts too.
Serotonin: why mood and motivation can dip
Serotonin is often referred to as a “feel-good” neurotransmitter, but its role extends beyond mood. It’s also involved in motivation, appetite and cognitive function. Research has shown that serotonin activity is influenced by light exposure. During brighter months, serotonin turnover tends to be higher. As daylight decreases, this activity can reduce.
This doesn’t necessarily mean you’ll feel low in mood, but it can show up more subtly as:
- Reduced motivation
- Feeling flatter or less driven
- A sense that things require more effort than usual
For many people, this shift is gradual enough to go unnoticed – until it accumulates.
Melatonin: why your sleep can change
Melatonin is the hormone that helps regulate your sleep–wake cycle. It rises in response to darkness, signalling to your body that it’s time to wind down. As nights become longer, melatonin production can begin earlier and last longer.
In theory, this is supposed to support sleep. But in practice, especially when paired with modern lifestyles, it can lead to:
- Feeling sleepier earlier in the evening
- Difficulty waking in the morning
- A sense of grogginess, heaviness or slower starts to the day
This is particularly noticeable if your exposure to natural morning light is limited, or if artificial light is extending your evenings – which is also why addressing these habits can make a profound difference to sleep.
Your circadian rhythm: the ripple effect
When serotonin and melatonin shift, your circadian rhythm shifts with them. And because this rhythm influences so many systems in the body, the effects can be widespread.
You might notice:
- Changes in energy patterns across the day
- Different hunger cues or cravings
- Altered focus or mental clarity
- A reduced tolerance to stress
This is why the experience of “feeling off” at this time of year can be difficult to pinpoint. It’s not just one thing, it’s a system-wide adjustment.
Why this matters
I’ve often seen people interpret these changes as a personal shortcoming. They assume they need to push harder. Be more disciplined. Or drink more coffee! But what’s actually happening is physiological. Your body is adapting to a different environment. And when that adaptation is disrupted, it can place additional strain on the nervous system, making everything feel more effortful. Over time, this can add to the stress load on the body, which has its own flow on effect on energy, digestion, hormones and so much more.
For some, these changes are mild – they may not even really notice a shift at all. For others, they can feel significant. There’s even a recognised condition, seasonal affective disorder, where these biological shifts lead to more pronounced changes in mood and energy. But you don’t need to meet clinical criteria to feel the effects of seasonal change. Even small shifts in light exposure can influence how you feel day to day.
Working with your biology, not against it
The most important takeaway is this: Your body is not being unpredictable. It’s responding to signals. And at this time of year, light is one of the most powerful signals it receives. When you understand this, it opens up a different way of approaching your health.
Instead of asking, “What’s wrong with me?”, you can ask, “What is my body responding to, and how can I support it?” Because often, the changes you’re feeling are not a problem to fix. They’re a message to listen to.
