The Melatonin-Light Connection: Why Darkness is a Biological Necessity

Author: Rohan Smith | Functional Medicine Practitioner | Adelaide, SA

Our ancestors’ lives were shaped by natural light and darkness. Today, bright indoor lighting and screens extend “daytime biology” deep into the evening. At Elemental Health and Nutrition, Rohan Smith helps Adelaide patients understand how modern light exposure can disrupt circadian timing and sleep quality—often contributing to non-restorative sleep and next-day fatigue. (1,2,3)

Quick Answer: How does light affect my sleep?

Your brain produces a hormone called melatonin, which is essential for sleep maintenance and night-time repair signalling. Melatonin production is triggered by darkness and regulated by your circadian clock. Evening exposure to artificial light—especially short-wavelength (“blue-enriched”) light—can suppress melatonin and delay its normal onset. (1,2,3)

The result: Even typical room light in the hours before bed has been shown to delay melatonin onset and shorten melatonin duration (by around 90 minutes in controlled conditions), which can contribute to lighter, more fragmented sleep and “morning brain fog.” (1)

Core Concept: The role of your “master clock” (SCN)

Inside your brain sits the suprachiasmatic nucleus (SCN), often described as the body’s “master clock.” It relies on light signals from your eyes to coordinate daily rhythms—sleep-wake timing, body temperature, and hormone patterns. (2,4,5)

When you look at bright screens or sit under strong indoor lighting late at night, the SCN can interpret this as “daytime” input. This can suppress melatonin, keep core body temperature higher for longer, and delay sleepiness. (1,2,3)

Important clarification: “Deep sleep” usually refers to slow-wave sleep (NREM stage 3), while REM sleep is a separate stage associated with memory processing and emotional regulation. Circadian disruption and melatonin suppression may affect overall sleep architecture across the night, including both NREM and REM timing and continuity. (2,3)

10 signs you may be experiencing low or mistimed melatonin signalling

Melatonin is more than a sleep-related hormone; it also has antioxidant activity and interacts with multiple endocrine and immune pathways. (6) A disrupted light-dark cycle or delayed melatonin onset can be associated with: (1,2,3,6)

1. Poor sleep: difficulty falling asleep, frequent waking, or waking too early. (1,2)
2. Hormonal pattern disruption: melatonin interacts with estrogen-related pathways and may influence local estrogen synthesis in some tissues. (7,8) For broader endocrine context, see hormonal regulation and circadian rhythm disruption. (9)
3. Higher night-time blood pressure: melatonin has been studied for its relationship with nocturnal blood pressure regulation (results vary by formulation and population). (10,11,12)
4. Chronic pain sensitivity: altered melatonin patterns and sleep disruption are commonly observed in chronic pain states; melatonin has been studied in fibromyalgia and migraine contexts. (13,14,15)
5. Thyroid signalling effects: older endocrine literature suggests melatonin can interact with thyroid-related signalling at the central level. (9)
6. Mood changes: light-at-night exposure and circadian disruption are associated with mental health outcomes in population research; causality varies by study design. (16,17)
7. Bone remodelling support: melatonin has been studied for potential roles in bone formation and osteoblast activity. (18,19)
8. Breastfeeding rhythm issues: melatonin and prolactin follow coordinated night-time patterns in human studies. (20)
9. Increased hunger/weight gain pressure: sleep restriction and circadian disruption can alter appetite-regulating hormones such as leptin and ghrelin in controlled studies. (21,22)
10. “Brain fog” after poor sleep: sleep supports metabolic waste clearance processes in the brain (evidence strongest from animal and mechanistic studies). (23)

Solution/Test: A “digital sunset” strategy for Adelaide professionals

The goal is not perfection—it’s restoring a stronger contrast between bright daytime light and dim evening light so your circadian system can time melatonin appropriately. (1,2,3)

1) The 2-hour dim-light window

Aim for ~2 hours of dim light before bed (not just “no phone”). In experimental and real-world studies, evening light exposure—especially from light-emitting devices—can delay circadian timing and suppress melatonin. (1,2,3)

2) Reduce short-wavelength (“blue-enriched”) light after sunset

Blue-enriched light is more likely to suppress melatonin compared with longer wavelengths, based on human action-spectrum research. (4,5)

3) Consider blue-blocking strategies (when behaviour change isn’t enough)

Some people use amber/blue-blocking glasses or device settings to reduce short-wavelength exposure in the evening. These strategies are best used as support—rather than a substitute—for reducing overall brightness and stimulating content at night. (3,17)

4) Keep the bedroom darker and simpler

Even small light sources can signal “daytime” to the circadian system. Prioritise darkness and reduce unnecessary LEDs in the sleep environment. (1)

5) Evening nutrition: support the serotonin → melatonin pathway

Melatonin is synthesised from serotonin. Some people find a small, balanced evening snack helpful—e.g., a tryptophan-containing food paired with a small carbohydrate source—to support sleepiness. Individual responses vary, particularly with reflux, blood sugar instability, or night waking. (21,22)

6) Morning outdoor light exposure

Natural morning light can help “anchor” circadian timing, supporting earlier melatonin onset the following evening. (2)

When to consider a circadian reset (or clinical support)

• You fall asleep easily but wake unrefreshed or wake repeatedly through the night. (1,2)
• You get a “second wind” at night, then struggle to sleep at your intended bedtime. (2,3)
• You rely on caffeine to function most mornings, especially after adequate time in bed. (1,2)
• You work late-night shifts or frequently travel across time zones. (2,16)

Next steps

• Start with light: dim your evenings for 7–14 nights and track sleep onset, night waking, and morning energy. (1,2)
• Anchor mornings: get outdoor light early where possible, then keep evenings consistently dim. (2)
• Pair with basics: regular meal timing, consistent wake time, and a wind-down routine often amplify results. (2)

Key Insights

• Evening room light and screens can suppress melatonin and shorten the biological “night,” potentially worsening sleep quality. (1,2,3)
• Short-wavelength (“blue-enriched”) light is especially potent for melatonin suppression in human studies. (4,5)
• Sleep and circadian disruption can influence next-day energy, appetite signalling, blood pressure rhythms, and mood-related outcomes (associations vary by study type). (10,11,12,16,21)

Restore Your Natural Rhythm

If you’re waking tired or relying on caffeine to get through the day in Adelaide, your light-dark cycle may benefit from a reset. For patients with persistent non-restorative sleep, we commonly start with circadian basics (morning light, evening dimness, and routine consistency), then personalise the plan around symptoms, lifestyle, and health history.

Next step: If you’d like support, you can book with Rohan Smith at Elemental Health and Nutrition to discuss sleep and recovery strategies and how they may relate to chronic fatigue and non-restorative sleep.

References

1. Gooley JJ, Chamberlain K, Smith KA, et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. J Clin Endocrinol Metab. 2011;96(3):E463–E472. (1)
2. Chang AM, Aeschbach D, Duffy JF, Czeisler CA. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc Natl Acad Sci USA. 2015;112(4):1232–1237. (2)
3. Cajochen C, Frey S, Anders D, et al. Evening exposure to a LED-backlit computer screen affects circadian physiology and cognitive performance. J Appl Physiol. 2011;110(5):1432–1438. (3)
4. Thapan K, Arendt J, Skene DJ. An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans. J Physiol. 2001;535(Pt 1):261–267. (4)
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6. Reiter RJ, Mayo JC, Tan DX, Sainz RM, Alatorre-Jimenez M, Qin L. Melatonin as an antioxidant: under promises but over delivers. J Pineal Res. 2016;61(3):253–278. (6)
7. Cos S, Fernández R, Güézmes A, Sánchez-Barceló EJ. Melatonin modulates aromatase activity in MCF-7 human breast cancer cells. J Pineal Res. 2005;38(2):136–142. (7)
8. Álvarez-García V, González A, Alonso-González C, et al. Melatonin modulates aromatase activity and expression in endothelial cells (mechanistic evidence relevant to local estrogen synthesis). Oncol Rep. 2013;29(6):2057–2064. (8)
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