Melatonin, Sleep & Immune Health: What the Science Shows

Originally written by ZRT Laboratory author. Reproduced with permission. Last reviewed: May 2026.

Melatonin is widely known as the “sleep hormone” — but its biological role extends far beyond regulating the sleep-wake cycle. As a potent antioxidant, anti-inflammatory agent, and immune modulator, melatonin plays a critical role in protecting cells from oxidative damage, suppressing harmful inflammatory pathways, and supporting the body’s defence against viral and bacterial infection. Understanding melatonin’s broader functions — and the consequences of its age-related decline — has significant implications for long-term health.

What Is Melatonin and How Is It Produced?

Melatonin is a hormone produced by the pineal gland in the brain, primarily during the hours of darkness. Its secretion is triggered by the absence of light and peaks at around 2 a.m., signalling to the body that it is time to sleep and initiating the physiological processes associated with overnight repair and restoration.

Melatonin production is suppressed by light exposure — particularly blue-spectrum light from screens, LED lighting, and electronic devices. It is also disrupted by jet lag, shift work, and non-24 sleep-wake disorder. Beyond the pineal gland, melatonin is produced in smaller quantities by the gut, immune cells, and other tissues, where it acts locally as an antioxidant and immune regulator.

Melatonin’s Role in Immune Health and Inflammation

Antioxidant and Free Radical Scavenging

Melatonin is one of the most potent endogenous antioxidants known. It directly neutralises reactive oxygen species (ROS) and reactive nitrogen species, protecting DNA, proteins, and cell membranes from oxidative damage. Unlike many antioxidants, melatonin can cross all physiological barriers — including the blood-brain barrier and the mitochondrial membrane — providing antioxidant protection in compartments that other antioxidants cannot reach.

This broad antioxidant activity gives melatonin significant protective effects against conditions driven by oxidative stress, including cardiovascular disease, type 2 diabetes, neurodegenerative disease, and cancer. It also stimulates the production of endogenous antioxidant enzymes including glutathione peroxidase, superoxide dismutase, and catalase.

Anti-Inflammatory Activity and the NLRP3 Inflammasome

Melatonin exerts powerful anti-inflammatory effects through modulation of cytokine production and inhibition of key inflammatory signalling pathways, including NF-κB. Of particular clinical significance is its ability to inhibit the activation of the NLRP3 inflammasome — an intracellular protein complex that triggers the secretion of pro-inflammatory cytokines including IL-1β and IL-18.

Inflammasome activation is a normal component of the immune response to infection and injury. However, excessive or dysregulated inflammasome activation drives the kind of severe, systemic inflammation — sometimes called a cytokine storm — that underlies the most dangerous complications of viral respiratory infections, including acute respiratory distress syndrome (ARDS). Melatonin’s ability to modulate this pathway without suppressing the immune response entirely makes it a uniquely valuable immune regulator.

Melatonin and Viral Infection

Research has highlighted melatonin’s potential importance in the context of viral respiratory infections. Cytokines are, as one research group described them, “dangerous double-edged swords” in the context of viral infection: they are essential for immune defence but can also mediate and amplify the spread of infection and tissue damage when dysregulated. The NLRP3 inflammasome is a key mediator of the acute respiratory distress characteristic of severe viral pneumonia, and melatonin’s inhibitory effect on this pathway represents a potentially important protective mechanism.

Melatonin, Age, and Disease Vulnerability

Melatonin production follows a characteristic age-related trajectory. Levels are low in the first months of life, rise dramatically to peak between ages one and three (mean approximately 330 pg/mL), then decline through childhood and adolescence before showing a progressive but moderate decline through adulthood. By ages 70 to 90, night-time melatonin levels have fallen to approximately 30 pg/mL — less than 10% of peak childhood levels.

This age-related decline in melatonin parallels the increasing vulnerability to severe illness, oxidative stress-related disease, and impaired immune function seen in older adults. The relative protection that young children appear to have against severe viral respiratory illness — compared with older adults — may in part reflect their significantly higher melatonin levels and the associated antioxidant and anti-inflammatory protection this provides.

The progressive loss of melatonin with age also contributes to the deterioration of sleep quality, increased oxidative damage, reduced immune surveillance, and higher rates of cardiovascular disease, metabolic dysfunction, and neurodegeneration seen in older populations.

How to Support Melatonin Production Naturally

Several lifestyle practices can meaningfully support endogenous melatonin production:

• Protect evening darkness. Avoid bright light and blue-spectrum screens (phones, tablets, computers, televisions) for at least one to two hours before bed. Use blue-light-blocking glasses or warm-spectrum lighting in the evening.
• Sleep in complete darkness. Even low levels of light during sleep suppress melatonin production. Use blackout curtains or a sleep mask.
• Maintain consistent sleep timing. Going to bed and waking at consistent times reinforces the circadian rhythm that drives melatonin secretion.
• Get morning sunlight exposure. Bright light in the morning anchors the circadian clock, ensuring melatonin is produced at the appropriate time in the evening.
• Support serotonin production. Melatonin is synthesised from serotonin, which in turn is derived from tryptophan. Adequate dietary tryptophan (from turkey, eggs, dairy, nuts, and seeds) and vitamin B6 support this pathway.
• Manage stress. Chronic cortisol elevation suppresses melatonin production. Stress management practices that reduce evening cortisol — including mindfulness, gentle exercise, and relaxation techniques — support melatonin secretion.

Melatonin Supplementation: What the Evidence Shows

Melatonin supplementation is widely available and has a well-established safety profile at appropriate doses. Clinical evidence supports its use for:

• Improving sleep onset and sleep quality, particularly in older adults and those with disrupted circadian rhythms
• Managing jet lag and shift work-related sleep disruption
• Reducing oxidative stress markers at doses of 10–20 mg/day in clinical studies
• Primary insomnia, where a prolonged-release formulation of 2 mg/day has been used successfully

For general sleep support, typical over-the-counter doses range from 0.5 to 3 mg/day. Higher doses (10–20 mg) have been used in research contexts for antioxidant and anti-inflammatory effects. The principle of using the lowest effective dose applies — supraphysiological melatonin levels from excessive supplementation can cause next-day drowsiness and may disrupt the natural circadian rhythm if used inappropriately.

Individuals with autoimmune conditions should consult a healthcare provider before supplementing, as melatonin’s immune-modulating effects may be relevant in this context.

Our Sleep Hormone Test measures the urinary melatonin metabolite MT6s (6-sulphatoxymelatonin) at multiple time points across the day using dried urine spot collection — providing a detailed picture of your melatonin production pattern, circadian rhythm integrity, and whether supplementation or lifestyle changes are needed to optimise your sleep and immune health.

The Relationship Between Sleep, Cortisol, and Immune Function

Melatonin and cortisol exist in a reciprocal relationship: cortisol rises in the morning as melatonin falls, and melatonin rises in the evening as cortisol declines. When this rhythm is disrupted — by chronic stress, shift work, poor sleep hygiene, or adrenal dysfunction — both hormones are affected. Elevated evening cortisol suppresses melatonin production, impairing sleep quality and reducing the overnight antioxidant and immune-restorative functions that melatonin provides.

Assessing both melatonin and cortisol together provides the most complete picture of circadian rhythm health and its impact on immune function, sleep quality, and long-term disease risk. Our Neurotransmitter and Cortisol Test measures cortisol at four time points alongside key neurotransmitters — identifying whether adrenal dysregulation or neurotransmitter imbalance is contributing to disrupted sleep and impaired immune health.

Testing Your Melatonin Levels

For those who want to assess the adequacy of their melatonin production objectively, dried urine testing of the melatonin metabolite MT6s provides a practical and accurate method. Because melatonin is rapidly metabolised and excreted in urine as MT6s, urinary MT6s measured across multiple time points reflects the full diurnal melatonin production pattern — including the overnight peak that is critical for immune restoration and antioxidant protection.

Our Advanced Sleep Hormone Test provides an extended assessment of sleep-related hormones including melatonin metabolites, alongside adrenaline and noradrenaline — giving a comprehensive picture of the neuroendocrine factors affecting your sleep quality and overnight immune function.

Frequently Asked Questions

What does melatonin do for the immune system?

Melatonin supports immune health through multiple mechanisms: it is a potent antioxidant that neutralises free radicals and protects immune cells from oxidative damage; it modulates cytokine production to prevent excessive inflammation; and it inhibits the NLRP3 inflammasome, reducing the risk of the dysregulated inflammatory responses that drive severe illness. It also supports the overnight immune surveillance and repair processes that occur during deep sleep.

Why does melatonin decline with age?

Melatonin production by the pineal gland declines progressively from early childhood onwards, with the most significant decline occurring after age 40 and accelerating after 70. The mechanisms include calcification of the pineal gland, reduced sensitivity to light-dark signals, and age-related changes in the circadian clock. This decline contributes to poorer sleep quality, increased oxidative stress, impaired immune function, and higher rates of age-related disease in older adults.

How can I increase melatonin naturally?

The most effective natural strategies are: avoiding bright and blue-spectrum light in the two hours before bed; sleeping in complete darkness; maintaining consistent sleep and wake times; getting bright natural light exposure in the morning; managing chronic stress to reduce evening cortisol; and ensuring adequate dietary tryptophan and vitamin B6 to support the serotonin-melatonin synthesis pathway.

Is melatonin supplementation safe?

Melatonin has a well-established safety profile at appropriate doses. For sleep support, doses of 0.5 to 3 mg are typically effective and well tolerated. Higher doses used in research for antioxidant effects (10–20 mg) appear safe in short-term studies. The main adverse effect of excessive dosing is next-day drowsiness. Individuals with autoimmune conditions should seek medical advice before supplementing.

How is melatonin tested?

Melatonin is most accurately assessed through urinary measurement of its primary metabolite, 6-sulphatoxymelatonin (MT6s), collected at multiple time points across the day using dried urine spot samples. This method captures the full diurnal production pattern without requiring blood draws or clinic visits. Saliva melatonin testing is also available and reflects the free, bioavailable fraction of the hormone.

Originally written by ZRT Laboratory author. Reproduced with permission. Last reviewed: May 2026.