Your body clock runs on light. Morning light tells it to wake up and start producing energy; darkness tells it to wind down. When the clocks change, that signal shifts overnight, but your hormones take days to catch up.
If your body is already managing a health condition, that mismatch can show up as heavier mornings, broken sleep, low mood, sugar cravings or flare-ups of existing symptoms. Conditions like fatigue syndromes, fibromyalgia, blood sugar imbalance, IBS, perimenopause and seasonal low mood are often especially sensitive to it. The good news is that small, consistent signals help your body re-set:
Dim the lights after dinner. Lamps instead of overhead lights help your evening wind-down.
Get daylight early. Ten minutes by a bright window counts if a walk isn’t possible.
Keep meal times steady. Food timing is a second clock signal for your body.
What’s actually happening inside your body
On Sunday 25 October the UK clocks go back an hour. On paper, it’s an extra hour in bed. In reality, it’s one more nudge to a body clock that has already been adjusting to shorter, greyer days since late summer.
Deep in your brain sits a master clock, the suprachiasmatic nucleus. It uses light coming in through your eyes to set the timing of almost everything else: when you feel alert, when you feel hungry, how you handle sugar, and when you get sleepy. Researchers describe this as the clock being “entrained” by daylight (Manfredini et al., 2018).
Two hormones do a lot of the heavy lifting:
- Cortisol is your get-up-and-go hormone. It naturally rises in the first hour after waking, and bright morning light gives that rise a boost. In one study, an hour of ordinary indoor-bright light after waking lifted the morning cortisol peak by around a third, while the same light in the evening made no difference (Scheer & Buijs, 1999).
- Melatonin is your night-time signal. Darkness lets it rise; light, even ordinary indoor light, holds it back. In one study, normal room lighting in the evening delayed melatonin’s start in almost everyone and cut its nightly run by about 90 minutes (Gooley et al., 2011).
When the clocks change, your daily routine moves overnight, but these rhythms shift gradually. For most people that takes a few days. For people whose rhythms are already out of step, adjusting can take up to one to two weeks (Blank et al., 2026). A 2025 review of 27 studies linked clock changes with poorer sleep and more daytime sleepiness, especially in “night owls” (Sleep Medicine Reviews, 2025). And that “extra hour” in autumn? There’s little evidence people actually get it, and five mornings of waking earlier by the body’s clock can add up to a net sleep loss across the week (Harrison, 2013).
It’s worth being honest about the science here: the autumn change is generally gentler than the spring one, and population studies on mood are mixed (Lewis et al., 2026). But averages hide individuals. If your energy, sleep or blood sugar is already on a knife-edge, a small shift can be the thing that tips it.
Why it can feel bigger when you’re already managing something
A body that’s coping with a health condition is often running with less in reserve. Here’s how the seasonal shift can land in a few common situations.
Fatigue and fibromyalgia. Unrefreshing sleep is one of the hallmarks of fibromyalgia, and researchers now see sleep problems as both a cause and a consequence of symptoms (Miró & Prados, 2012). Studies of the body clock itself are mixed: one carefully controlled study found melatonin and cortisol rhythms in women with fibromyalgia looked much like everyone else’s (Klerman et al., 2001). That’s actually encouraging. It suggests the clock isn’t “broken”, but that the sleep and energy systems around it are more easily knocked. When sleep slips, pain and fatigue often follow.
Blood sugar balance. Your ability to handle sugar runs on a daily rhythm too. In a lab study where people ate and slept at the “wrong” biological time, blood sugar rose by 6% despite 22% more insulin, and three of eight participants briefly showed after-meal readings in the prediabetic range (Scheer et al., 2009). That was an extreme 12-hour shift, not a one-hour clock change, but it shows the direction of travel. Tiredness and fatigue also tend to nudge us towards quick-energy foods, which is why sugar cravings often creep in during darker months.
IBS and gut symptoms. Your gut has its own clock, which is part of why many people’s bowels are most active in the morning. Nurses working rotating shifts, whose clocks are constantly shifting, had higher rates of IBS and abdominal pain than those on regular day shifts (Nojkov et al., 2010). A routine that wobbles can show up as bloating, constipation or a more unsettled tummy.
Perimenopause. Changing oestrogen and progesterone, plus night sweats, already make sleep harder for many women in midlife. Sleep difficulties are linked with the menopausal transition over and above the effects of age (Baker et al., 2018). Add darker mornings and a shifted routine, and there’s less buffer to absorb it.
Seasonal low mood. The NHS describes seasonal affective disorder as a form of depression usually linked to reduced winter daylight, which may affect melatonin, serotonin and the sleep–wake rhythm (NHS, 2025). Even without a diagnosis, many people notice their mood and motivation dip and fatigue increase as the days shorten.
Gentle ways to help your body re-set
You don’t need a complete overhaul. Think of these as clear, kind signals that tell your body what time it is. Pick one or two that feel doable and build from there.
1. Make morning light your anchor. Light soon after waking is the strongest signal your clock gets, and clinicians recommend it specifically to ease clock-change disruption (Blank et al., 2026). Outdoors is best, even on a cloudy day. If energy is limited, a cup of tea on the doorstep or ten minutes by your brightest window still counts. If you live with fatigue or fibromyalgia, keep this within your pacing plan rather than pushing for a long walk.
2. Ease in rather than jumping. If you can, shift your bedtime and wake time by 15–20 minutes a day for the few days around the change, rather than all at once (Blank et al., 2026). If the clocks have already gone back, simply keep your wake time steady and let bedtime follow.
3. Let meal times do some of the work. In one study, moving meals five hours later shifted the body’s blood sugar rhythm by the same amount, even though the brain’s master clock didn’t move (Wehrens et al., 2017). So steady meal times help keep your metabolism in step. A breakfast with some protein and fibre, eaten within a couple of hours of waking, is a gentle way to say “the day has started” and can help steady energy and cravings.
4. Dim the evening. Ordinary room lighting is enough to delay melatonin (Gooley et al., 2011). After dinner, switch to lamps, lower screen brightness, and save scrolling for earlier in the evening.
5. Keep a steady rhythm. The NHS suggests getting outside in daylight every day, moving regularly and going to bed and getting up at the same times (NHS, 2025). Consistency matters more than perfection.
6. Think about vitamin D. Between October and early March, UK sunlight isn’t strong enough for us to make the vitamin D we need. The Government advises everyone to consider a daily 10 microgram (400 IU) supplement through autumn and winter (NHS, n.d.). If you take medication or have a health condition, check with your GP or practitioner first.
7. Watch the afternoon pick-me-ups. When mornings feel heavy, it’s natural to reach for extra coffee or something sweet later in the day. Try keeping caffeine to the morning and having a balanced snack ready for that mid-afternoon dip.
Be kind to yourself this week
If the next couple of weeks feel harder with increasing fatigue, it isn’t a sign that you’re going backwards. Your body is adjusting to a real change, and it’s doing that on top of everything else it’s already managing. Give it clear signals, give it a little time, and give yourself some grace.
If symptoms flare and don’t settle after a couple of weeks, or your mood drops in a way that worries you, please speak to your GP. And if you’d like support building a seasonal routine that fits your body and your life, I’d love to help you find what works for you.
Speak soon, Tara.
Kusala Nutrition & Lifestyle – Optimum Health through Wholesome Living.
This article is for general information and isn’t a substitute for personalised medical advice.
References
- Baker, F.C., de Zambotti, M., Colrain, I.M. & Bei, B. (2018) ‘Sleep problems during the menopausal transition: prevalence, impact, and management challenges’, Nature and Science of Sleep, 10, pp. 73–95. Link
- Blank, L., Khorsandi, J., England-Kennedy, E., Banerjee, S., Kopera-Frye, K., Sagaribay, R., Khubchandani, J. & Batra, K. (2026) ‘When the clock shifts: a comprehensive review of daylight-saving time (DST), circadian disruption, and neuropsychological risk in chronic mental illness’, Brain Sciences, 16(5), 522. Link
- Gooley, J.J. et al. (2011) ‘Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans’, Journal of Clinical Endocrinology & Metabolism, 96(3), pp. E463–E472. Link
- Harrison, Y. (2013) ‘The impact of daylight saving time on sleep and related behaviours’, Sleep Medicine Reviews, 17(4), pp. 285–292. Link
- Klerman, E.B. et al. (2001) ‘Circadian rhythms of women with fibromyalgia’, Journal of Clinical Endocrinology & Metabolism, 86(3), pp. 1034–1039. Link
- Lewis, P. et al. (2026) ‘A systematic review of epidemiological studies into daylight-saving time & health identifying beneficial & adverse effects’, European Journal of Epidemiology. Link
- Manfredini, R., Fabbian, F., Cappadona, R. & Modesti, P.A. (2018) ‘Daylight saving time, circadian rhythms, and cardiovascular health’, Internal and Emergency Medicine, 13, pp. 641–646. Link
- Miró, E. & Prados, G. (2012) ‘Fibromyalgia and sleep: a review’, Revista de Neurología, 54(4). Link
- NHS (2025) Seasonal affective disorder (SAD). Link
- NHS (n.d.) Vitamin D. Link
- Nojkov, B., Rubenstein, J.H., Chey, W.D. & Hoogerwerf, W.A. (2010) ‘The impact of rotating shift work on the prevalence of irritable bowel syndrome in nurses’, American Journal of Gastroenterology, 105(4), pp. 842–847. Link
- Scheer, F.A.J.L. & Buijs, R.M. (1999) ‘Light affects morning salivary cortisol in humans’, Journal of Clinical Endocrinology & Metabolism, 84(9), pp. 3395–3398. Link
- Scheer, F.A.J.L., Hilton, M.F., Mantzoros, C.S. & Shea, S.A. (2009) ‘Adverse metabolic and cardiovascular consequences of circadian misalignment’, Proceedings of the National Academy of Sciences, 106(11), pp. 4453–4458. Link
- Sleep Medicine Reviews (2025) ‘The effects of daylight saving time and clock time transitions on sleep and sleepiness: a systematic review’ (Romigi group, UniCamillus/Neuromed). Link
- Wehrens, S.M.T. et al. (2017) ‘Meal timing regulates the human circadian system’, Current Biology, 27(12), pp. 1768–1775. Link