The Science of the Winter Slump

There is nothing quite like leaving a lecture at 3pm, the sun already set. It’s November — deadlines are piling up, but you can’t seem to focus on work beyond the early afternoon sunset. One week you are revising lying in St Mary’s Quad, and the next it’s pitch black before you have even left your afternoon lecture. The so-called ‘winter slump’ feels personal, but in reality, it’s deeply biological. Our brains are responding exactly as they are built to — just not in ways that support a modern student lifestyle. 

At the centre of this shift is the circadian rhythm. This is your body’s natural 24-hour clock, keeping you operating on a healthy sleep-wake cycle. Light is the body’s timekeeper, received by the suprachiasmatic nucleus (SCN) in the hypothalamus of the brain. Throughout the day, genes located in the SCN send signals to control activity in the body. Earlier sunsets and later sunrises lengthen the period of darkness, leading to a longer window of melatonin secretion. Melatonin is a hormone secreted by the pineal gland, telling your body it’s time to get ready to rest when darkness begins. In practice, this means we start feeling tired earlier in the afternoon, even when we have had enough sleep. 

Daylight also plays a major role in regulating serotonin pathways in the brain. Serotonin is a neurotransmitter and hormone, responsible for regulating mood, motivation, and the brain’s reward system. Serotonin neurons in the dorsal raphe nucleus in the brain are directly modulated by light-driven signals received from the eyes. Reduced daylight exposure in winter suppresses serotonin pathways. This effect is amplified as serotonin is the biochemical precursor of melatonin. During extended winter nighttime hours, more serotonin is converted into melatonin, reducing the amount of serotonin available during the day. Reduced serotonin is strongly associated with decreased motivation, irritability, and a blunted reward response.  

On top of all of this, our immune system is also weakened. Melatonin is not only a sleep hormone, but also acts as an immune modulator, helping to regulate the development and activity of T cells. These cells are essential in antiviral responses, helping to protect us from common coughs and colds. During winter, the longer duration of melatonin secretion disrupts the normal timing of T cell production, causing T cells to become less efficiently activated.

These biological changes directly affect cognition. A disrupted circadian rhythm leads to poorer attention and working memory. Serotonin dips reduce our motivation and reward response, making academic tasks feel disproportionately effortful. It is hard to think clearly through the brain fog a cold can bring. And worst of all, this period coincides with deadline season and revision weeks.

There are practical ways to support the brain, even during these dark months. Morning daylight is one of the most powerful tools, helping to regulate your circadian rhythm. Trying not to hit snooze on the alarm for your 9am is essential, as the early-morning walk to the lecture theatre could change the rest of your day. Light therapy lamps can also be useful, and taking short breaks outside mid-study sessions can help to boost serotonin and motivation while re-anchoring the circadian clock.

Movement also matters. Exercise, even a brisk walk to Taste to grab a chai, stimulates serotonin and increases alertness. Keeping a consistent sleep routine helps to stabilise melatonin secretion, preventing the drift that makes afternoons so difficult. None of these strategies requires dramatic lifestyle changes; they are small adjustments designed to work with biology rather than against it.

The winter slump is real — but it’s not permanent. As the term ends and daylight slowly returns, our bodies reset. Until then, understanding the science behind the slump can make the experience feel less like a personal failing and more like what it really is: the brain doing its best to adapt to a darker world.

Image from Wikimedia Commons