Why You’re More Tired in Winter: Melatonin, Sleep, and How to Fix Your Circadian Rhythm

As the days shorten and a distinct chill fills the air, do you feel a shift in your energy? For many of my patients, the arrival of winter brings a predictable and frustrating “energy crash.” They describe a sense of lethargy, a desire to “hibernate,” and a persistent grogginess that no amount of coffee seems to fix. As a functional medicine physician, I can assure you this is not just “in your head.” It’s a real, biological phenomenon rooted in a mismatch between our ancient internal clocks and the demands of modern life.

Vague advice like “get more sun” is frustratingly incomplete. In this blog we will delve into the root cause of winter fatigue—a disrupted circadian rhythm, explore the intricate science of melatonin and light, uncover the systemic consequences of a misaligned body clock, and, most importantly, detail a step-by-step protocol to reset your system and conquer seasonal fatigue for good.

What Causes the “Winter Energy Crash”? Understanding the Science of Seasonal Fatigue

From a clinical perspective, the most common complaint I hear from November through February is a profound lack of energy. This “winter fatigue” or seasonal energy crash is not a character flaw; it’s a physiological response to a powerful environmental cue: the reduction of light. Our bodies are hardwired to respond to seasonal changes, a relic of our evolutionary past. The core of this response lies in the intricate dance between a key hormone, melatonin, and our body’s master timekeeper, the circadian rhythm.

Research has long established a fundamental link between melatonin and seasonal rhythms, noting that our bodies are exquisitely sensitive to the length of the day (Wehr, 1997). However, in our modern world, this ancient system is often confounded. We are no longer governed solely by the sun; we are influenced by artificial lighting, work schedules, and social obligations. This creates a complex interplay where our internal biological time can fall out of sync with the local clock time, a phenomenon that is particularly pronounced during the dramatic light shifts of winter (Skeldon & Dijk, 2021).

How Does Melatonin Work and Why Does It Spike Earlier in the Winter?

Melatonin is often called the “hormone of darkness,” and for good reason. Its production by the pineal gland in the brain is suppressed by light and stimulated by darkness. It doesn’t so much “put you to sleep” as it signals to your entire body that it’s nighttime and time to prepare for rest.

In the winter, darkness arrives earlier in the afternoon. This environmental cue triggers your pineal gland to begin releasing melatonin sooner than it does during the long days of summer. This earlier spike in melatonin is why you might feel sleepy at 7 p.m. and struggle to stay productive in the evening. As pioneering research has shown, the duration of nightly melatonin secretion is directly proportional to the length of the night, meaning winter’s long nights create a longer melatonin signal (Wehr, 1997). This seasonally-driven variation in the circadian melatonin rhythm is a primary driver of that classic winter fatigue and desire to sleep more (Skeldon & Dijk, 2021.

What Is Circadian Rhythm and How Does Seasonal Darkness Disrupt It?

Your circadian rhythm is your body’s innate, near-24-hour internal clock that orchestrates a vast array of physiological processes, from your sleep-wake cycle and hormone release to metabolism and body temperature. The “master clock” that governs this entire system is a tiny cluster of nerve cells in the hypothalamus called the suprachiasmatic nucleus (SCN).

Think of the SCN as a master conductor that needs to be synchronized with the outside world every single day. Its most powerful synchronizing cue, or Zeitgeber (German for “time-giver”), is light. Morning light exposure, in particular, is critical; it hits the retina, sends a signal directly to the SCN, and essentially says, “It’s morning! Reset the clock, suppress melatonin, and start the day.”

The problem in winter is twofold. First, there is simply less daylight available. Second, our exposure to it is often minimal. We wake up in darkness, commute in low light, work indoors under weak artificial light, and leave work in darkness. This lack of a strong, bright morning light signal can cause our internal SCN clock to drift later, a phenomenon known as phase delay. This creates a desynchronization between our internal biological clock and our external social clock (our 9-to-5 schedule). The result is that classic feeling of being tired all day but wired at night, struggling to wake up, and never feeling truly rested. The powerful, resetting effect of light on human circadian rhythms is well-documented (Gooley, 2017), and its absence is a key cause of the mood and sleep changes many experience in winter (Blume et al., 2019).

The Far-Reaching Impact of a Disrupted Winter Clock

Feeling tired is just the tip of the iceberg. As a functional medicine practitioner, my focus is on the interconnectedness of the body’s systems. Chronic circadian disruption during the winter months is not a minor inconvenience; it’s a significant physiological stressor with systemic consequences that can impact your mental health, immune function, and hormonal balance.

It’s crucial to understand that seasonal mood changes exist on a spectrum. Many people experience the mild “winter blues,” characterized by lethargy and low motivation. For a smaller percentage, these symptoms are severe enough to meet the clinical criteria for Seasonal Affective Disorder (SAD), a formal type of depression. Understanding where you fall on this spectrum is an important step toward seeking the right level of support. For more information on the clinical diagnosis, the American Psychiatric Association on SAD is an authoritative resource.

Is Poor Sleep in the Winter Linked to Mood, Immunity, and Hormones?

The answer is an emphatic yes. When your master clock is desynchronized, it throws the timing of countless downstream processes into disarray, creating a cascade of negative effects.

• Mood and Neurotransmitters: Circadian rhythm disruption is strongly linked to mental health disorders (Walker, et al., 2020). The SCN helps regulate neurotransmitters like serotonin, which is critical for mood regulation. Reduced sunlight exposure in winter can lead to lower serotonin activity, contributing to feelings of depression and anxiety that characterize the winter blues and SAD (Blume et al., 2019).
• Hormones and Metabolism: The sleep and circadian disturbance common in winter has a profound impact on your endocrine system. It can disrupt the natural 24-hour rhythm of cortisol (your primary stress hormone), leading to fatigue and increased stress perception. Furthermore, it can dysregulate metabolic hormones like insulin, ghrelin (the “hunger hormone”), and leptin (the “satiety hormone”), which explains the intense carbohydrate cravings and potential for weight gain many experience during winter (Kim, et al., 2015).
• Immune Function: Your immune system also operates on a circadian schedule. Proper clock function is necessary for a robust and balanced immune response. Disruption can impair immune surveillance, potentially making you more susceptible to infections—a timely concern during the winter cold and flu season. Boosting your immune system through food is one way to support your health during these cold months.

How Can I Reset My Circadian Rhythm?

Understanding the science is the first step; taking control is the next. This section is your clinical protocol—a series of evidence-based, actionable strategies designed to powerfully resynchronize your internal clock with your desired schedule. These are not just tips; they are therapeutic interventions that target the underlying biology of your circadian rhythm (Zhang, 2025). By systematically strengthening your body’s primary time-keeping signals, or Zeitgebers, you can effectively combat winter fatigue at its source.

How Much Light Do You Need Daily to Reset Your Sleep-Wake Cycle in Winter?

Light is your most powerful tool. The goal is to mimic a summer sunrise by exposing yourself to very bright light shortly after waking. This sends a strong “daytime” signal to your SCN, correcting the phase delay, suppressing morning melatonin, and anchoring your entire 24-hour rhythm. This is the science of phototherapy.

The science of light-induced resetting of circadian rhythms is clear: timed light exposure is a potent therapeutic tool (Gooley, 2017), with profound effects on sleep and mood (Blume et al., 2019). For most people, this means using a light therapy box for 20-30 minutes within the first hour of waking.

Physician’s Tip: How to Choose and Use a Light Therapy Box

When selecting a device, look for one that provides an exposure of 10,000 lux of light, the clinically effective intensity. Ensure it is designed to filter out harmful UV light. For use, position the box at an angle (not directly into your eyes) about 16 to 24 inches from your face. You can do this while eating breakfast, checking emails, or reading. Consistency is key.

Can Morning and Evening Routines Improve Your Circadian Rhythm During Winter?

Absolutely. Consistency is the bedrock of a stable circadian rhythm. Think of these routines as behavioral therapy for your body clock (Zhang, 2025). They create predictable “anchor points” that reinforce the sleep-wake cycle your light therapy is helping to establish.

Your Morning Circadian-Anchor Routine:

1. Consistent Wake Time: Wake up at the same time every single day, even on weekends. This is the single most important habit for a stable rhythm.
2. Immediate Light: Within minutes of waking, begin your 20-30 minute light therapy session.
3. Hydrate and Move: Drink a large glass of water and do 5-10 minutes of light stretching or movement. This helps to raise core body temperature and further signal that the day has begun.

Your Evening Wind-Down Routine:

1. Dim the Lights: Two to three hours before bed, dim all the lights in your home. Use warm-toned bulbs instead of bright, blue-toned overhead lights.
2. Block Blue Light: Avoid screens (phones, tablets, TVs) in the final 60-90 minutes before bed. If you must use them, install a blue-light-filtering app or wear blue-light-blocking glasses. This prevents artificial light from suppressing your natural evening melatonin surge.
3. Consistent Bedtime: Go to bed at the same time each night, allowing for 7-9 hours of sleep.

From a functional medicine perspective, these routines do more than just set your clock; they reduce allostatic load (the “wear and tear” from chronic stress) and support healthier adrenal function by creating predictability in a chaotic world.

What Foods and Nutrients Support Melatonin and Serotonin During Dark Months?

Nutrition is a powerful modulator of your neurochemistry and energy levels. The intense craving for carbohydrates in winter is a biological drive; carbs can temporarily increase levels of serotonin in the brain. The key is to satisfy this drive with smart choices.

The biochemical pathway for your key sleep and mood molecules starts with an amino acid called tryptophan. Your body converts tryptophan into 5-HTP, which is then converted into serotonin (your “feel-good” neurotransmitter). At night, in the absence of light, serotonin is then converted into melatonin.

To support this pathway, focus on:

• Tryptophan-Rich Foods: Include sources like turkey, chicken, nuts, seeds, oats, and beans in your diet.
• Nutrient Co-factors: This conversion process requires key vitamins and minerals. Ensure adequate intake of Magnesium (leafy greens, almonds, avocado), Zinc (seeds, legumes, meat), and B-Vitamins (especially B6, found in fish, poultry, and chickpeas).
• Complex Carbohydrates: Instead of simple sugars that cause energy crashes, opt for complex carbs like sweet potatoes, quinoa, oats, and whole-wheat bread. Pairing these with a protein source can provide a sustained release of energy and support serotonin production without the spike and dip.

This focus on whole, nutrient-dense foods aligns with a functional medicine approach, which recognizes that dysregulated metabolism is often intertwined with circadian disruption (Kim, et al., 2015).

Natural Ways to Reset Your Circadian Rhythm Without Supplements

While light therapy is a cornerstone, several other lifestyle strategies are powerful therapeutic interventions that reinforce its effects (Zhang, 2025).

Top 5 Non-Supplement Strategies:

1. Timed Exercise: Aim for 30 minutes of moderate exercise (brisk walking, jogging, cycling) in the morning or early afternoon. This raises core body temperature and promotes alertness. Avoid intense workouts within 3 hours of bedtime.
2. Get Natural Light: Even on a gray, overcast day, the light outdoors is exponentially more powerful than indoor lighting. Take a 15-20 minute walk at midday to get a crucial dose of natural light.
3. Maintain a Strict Schedule: As mentioned, a consistent sleep-wake schedule is non-negotiable. This is the anchor for your entire rhythm.
4. Control Your Temperature: Your body temperature naturally drops at night to facilitate sleep. Keep your bedroom cool (around 65°F or 18°C) to support this process. A warm bath 90 minutes before bed can also help by causing a subsequent drop in core body temperature.
5. Time Your Meals: Avoid large, heavy meals within 3 hours of bedtime. Digestion is an active process that can interfere with sleep quality. Confining your eating to a consistent 8-10 hour window during the day can also help strengthen circadian signals.

Clinical Considerations & Patient FAQs

As a physician, it’s my responsibility to provide nuanced guidance on common questions and concerns. While the blueprint above is safe and effective for most people, it’s vital to address the use of supplements and the question of sleep duration with care. If your symptoms are severe, persistent, or accompanied by feelings of hopelessness, it is essential to consult a healthcare professional.

Should You Take Melatonin Supplements in the Winter? Benefits, Risks, and Best Practices

Melatonin is one of the most misunderstood supplements. While it’s widely available and marketed as a simple sleep aid, its use requires precision. Taking it incorrectly can worsen your circadian disruption.

The body already produces more melatonin for a longer duration in winter (Wehr, 1997)., (Skeldon & Dijk, 2021). The goal isn’t necessarily more melatonin, but melatonin at the right time. For circadian phase delay, a very low dose of melatonin (0.5mg to 1mg) taken in the afternoon (e.g., 3-5 hours before your natural melatonin onset) can help advance your internal clock, making you sleepy earlier. Taking a high dose at bedtime acts more as a hypnotic or “sledgehammer,” which may help you fall asleep but does little to correct the underlying timing issue.

Risks and Considerations:

• Unregulated Market: In the U.S., melatonin is a supplement, not a drug, and is not regulated by the FDA for purity or dosage. Studies have found that the actual content in commercial products can vary wildly from what’s on the label. Look for products with third-party testing seals (like USP or NSF).
• Incorrect Timing: Taking melatonin in the morning or too late at night can further shift your clock in the wrong direction, exacerbating grogginess.
• Side Effects: Potential side effects include dizziness, headaches, and next-day drowsiness when the dose is incorrect for your body.

Who Should Avoid Melatonin?

You should always consult your physician before taking melatonin, especially if you are pregnant or breastfeeding, have an autoimmune condition, a seizure disorder, or depression.

How Much Sleep Do You Actually Need in Winter?

While the longer melatonin signal in winter may make you feel like you need more sleep, the fundamental need for 7-9 hours of quality sleep per night does not change for most adults. The key is to differentiate between restorative sleep and the unrefreshing hypersomnia (oversleeping) often associated with the winter blues and SAD.

Sleeping for 10-11 hours but still waking up exhausted is a classic sign of poor sleep quality and circadian misalignment. This type of sleep disturbance is linked to negative metabolic (Kim, et al., 2015) and mental health outcomes (Walker, et al., 2020). Rather than focusing solely on hours in bed, focus on sleep efficiency—the percentage of time in bed that you are actually asleep. Aim to wake up feeling rested. Following the circadian reset blueprint will improve your sleep quality, making the hours you do get more restorative. Tracking your sleep times, energy levels, and mood in a journal can be a valuable tool to discuss with your healthcare provider.

Take Back Your Winter

Winter fatigue is not an inevitable sentence of seasonal suffering. It is a predictable biological response to a weak and misaligned light signal. By understanding the elegant science of your internal clock, you now have the power to intervene.

By strategically managing light with phototherapy, cementing your schedule with consistent routines, and supporting your neurochemistry with targeted nutrition, you are providing your body with the powerful, unambiguous signals it needs to thrive, even on the darkest days.

To put this knowledge into practice, start by implementing one new habit from the blueprint today. For those with persistent or severe symptoms that are impacting your quality of life, consider scheduling a consultation to explore personalized functional medicine testing and develop a comprehensive treatment plan tailored to your unique physiology.

This article is for informational and educational purposes only and does not constitute medical advice. The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Do not disregard professional medical advice or delay in seeking it because of something you have read in this article.

References

1. Wehr, T. A. (1997). Melatonin and Seasonal Rhythms. Journal of Biological Rhythms, 12(6), 518–527. https://doi.org/10.1177/074873049701200605.
2. Skeldon, A. C., & Dijk, D. J. (2021). Weekly and seasonal variation in the circadian melatonin rhythm in humans: Entrained to local clock time, social time, light exposure or sun time?. Journal of Pineal Research, 71(2), e12746. https://doi.org/10.1111/jpi.12746.
3. Gooley, J. J. (2017). Light-induced Resetting of Circadian Rhythms in Humans. Journal of the Illuminating Engineering Institute of Japan, 41, 69-76. https://doi.org/10.2150/jstl.ieij160000594.
4. Blume, C., Garbazza, C., & Spitschan, M. (2019). Effects of light on human circadian rhythms, sleep and mood. Somnologie, 23(3), 147–156. https://doi.org/10.1007/s11818-019-00215-x.
5. Walker, W. H., 2nd, Walton, J. C., DeVries, A. C., & Nelson, R. J. (2020). Circadian rhythm disruption and mental health. Translational Psychiatry, 10(1), 22. https://doi.org/10.1038/s41398-020-0694-0.
6. Kim, T. W., Jeong, J. H., & Hong, S. C. (2015). The impact of sleep and circadian disturbance on hormones and metabolism. International Journal of Endocrinology, 2015, 591729. https://doi.org/10.1155/2015/591729.
7. Zhang, R. (2025). Therapeutic Interventions Targeting Circadian Rhythms. Theoretical and Natural Science, 20310. https://doi.org/10.54254/2753-8818/2025.20310.