The Science Of Hibernation (Sort Of)
Every year, around this time, I have some version of the same conversation with the patients in my clinic: "I just feel so much more tired in winter.", "I have no motivation to do anything in the evenings.", "Is something wrong with me, or is this normal?"
Here's the reassuring answer: it's normal. To a degree… And there's a fascinating reason behind it. We don't hibernate, per se, not in the way a bear does. But our bodies are far more responsive to seasonal light and temperature changes than most of us realise, and understanding this can completely change how you relate to your winter energy levels.
Your body is still reading the seasons
Humans evolved over thousands of years in environments with dramatic seasonal variation - long, light filled summer days and short, dark winter ones. Our biology adapted to this rhythm long before electric lighting, heated homes, blue screens and year-round productivity expectations existed. One of the most significant seasonal signals your body responds to is light exposure. Specifically, the ratio of daylight to darkness. This ratio directly influences melatonin production, the hormone responsible for regulating sleep, and has downstream effects on cortisol, mood-regulating neurotransmitters, and overall energy. In winter, with shorter days and less natural light, melatonin production increases and shifts earlier in the evening for many people. This isn't a malfunction, it's your body responding exactly as it's designed to. The mismatch comes from the fact that our schedules, screens, and obligations don't shift with it.
The role of vitamin D
Vitamin D (not really a vitamin, and actually a hormone) is synthesised in your skin in response to UVB exposure from sunlight and in winter, UVB levels drop significantly, sometimes for months at a time. Vitamin D isn't just about bone health. It plays a significant role in immune function, mood regulation, and even energy production at a cellular level. Many people experience a measurable drop in vitamin D status over winter, and this can contribute meaningfully to the fatigue, low mood, and reduced motivation that so many describe as "winter blues" or SAD (seasonal affective disorder). This is one of the most common things I check in winter consultations and one of the most common things I find low.
Cortisol, temperature, and energy conservation
Cold exposure is a genuine physiological stressor. Your body has to work harder to maintain core temperature, which has knock-on effects on your stress hormone patterns and energy allocation. There's also a slower digestive and metabolic shift that tends to happen in colder months. Historically, this would have supported fat retention and energy conservation through periods of food scarcity, which would’ve been extremely handy. However, in a modern context, it often shows up as a genuine pull toward heavier, warming foods, slower mornings, and less drive for high-intensity activity - which many people fight against, assuming it's laziness rather than physiology. It isn't laziness. It's an old, deeply wired pattern responding to a very real seasonal signal.
What to actually do about it
Understanding why this happens is the first step, but there's a lot you can do to work with your body rather than against it this winter. Morning light exposure matters more than almost anything else. Even on an overcast day, getting outside within the first hour of waking helps anchor your circadian rhythm and can significantly improve energy and mood throughout the day. Vitamin D testing is worth considering if you haven't had it checked recently - particularly if you're someone who spends most days indoors, has darker skin, or has a history of low levels. Supplementation, when appropriate, can make a noticeable difference. Eating with the season. Having those warming, slow-cooked, root vegetable and spice-rich meals. It isn't just comforting, it genuinely supports digestion and energy in a way that matches what your body is asking for. And finally; and this is the part I most want you to hear - some reduction in energy and motivation through winter is normal. You don't need to perform at full summer capacity twelve months a year. Working with your natural rhythms, rather than constantly overriding them, is not a failure. It's actually one of the most regulating things you can do for your nervous system.
If your winter fatigue feels more significant than this. Or if it's persistent, if it's affecting your daily function, or if something feels off beyond a normal seasonal dip - that's worth looking into a little deeper. There can be a lot going on underneath, and it's always worth understanding what's yours to simply ride out, and what's worth addressing. If that's you, I'd love to help.
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Photo by Chris Tellez on Unsplash