Beyond Sleep

A potent antioxidant, not just a hormone

Melatonin is a direct free radical scavenger that neutralizes hydroxyl radicals, hydrogen peroxide, singlet oxygen, and peroxynitrite [1]. Unlike most antioxidants that donate one electron per molecule, melatonin triggers an antioxidant cascade -- its metabolites (cyclic 3-hydroxymelatonin, AFMK, AMK) are themselves antioxidants, meaning a single melatonin molecule can scavenge up to 10 reactive oxygen species [1]. Reiter et al. described this as melatonin "under-promising but over-delivering" as an antioxidant.

Melatonin also upregulates endogenous antioxidant enzymes including glutathione peroxidase, superoxide dismutase, and catalase, while downregulating pro-oxidant enzymes like nitric oxide synthase [2]. This dual action -- direct scavenging plus enzyme regulation -- makes it uniquely effective.

Immune modulation

Melatonin acts as an immunomodulator rather than a simple immune stimulant. It enhances the production of natural killer cells, T-helper cells, and immunoglobulins during immune challenge, while also having anti-inflammatory properties that help prevent excessive immune responses [2]. This balance is why melatonin has been investigated in contexts ranging from infection response to autoimmune conditions. Carrillo-Vico et al. (2005) described melatonin as an "immune buffer" that amplifies immunity when needed and dampens it when overactivated [2].

Cancer research

Melatonin has shown anti-tumor activity in both in vitro and animal studies, particularly in hormone-dependent cancers. Hill et al. (2015) reviewed the evidence on breast cancer, finding that melatonin suppresses tumor growth through multiple mechanisms: inhibiting estrogen receptor signaling, reducing aromatase activity, modulating epigenetic pathways, and enhancing the cytotoxicity of chemotherapy drugs [4]. Night-shift workers, who have chronically suppressed melatonin due to light exposure at night, have consistently higher rates of breast and prostate cancer -- a relationship strong enough that the WHO classified night-shift work as a probable carcinogen (Group 2A).

Dosing: less is more

This is where most people go wrong. Over-the-counter melatonin supplements typically come in 3mg, 5mg, or 10mg doses, but research suggests that physiological doses of 0.3-0.5mg are often more effective for sleep than these supraphysiological amounts [3]. Lewy et al. found that low doses entrained circadian rhythms more effectively than high doses. Higher doses can cause morning grogginess, vivid dreams, and -- critically -- may desensitize melatonin receptors over time, potentially reducing your body's natural melatonin response.

Long-term supplementation at high doses may downregulate natural pineal production. If you do supplement, start with the lowest dose available (0.3-0.5mg), taken 30-60 minutes before your target bedtime.

Blue light destroys melatonin production

Your pineal gland produces melatonin in response to darkness. Blue light (460-480 nm wavelength) -- the dominant spectrum emitted by phones, tablets, and LED screens -- is the most potent suppressor of melatonin synthesis. Even moderate blue light exposure in the two hours before bed can delay melatonin onset by 90 minutes or more. This is covered in depth in the Sleep section on blue light and circadian rhythm.

Food sources of melatonin

Several foods contain meaningful amounts of melatonin:

• Tart cherries -- the richest known food source, particularly Montmorency cherries. Tart cherry juice concentrate has been shown in clinical trials to modestly improve sleep duration and quality.
• Pistachios -- contain exceptionally high levels of melatonin (about 660 ng/g), far more than most other nuts.
• Walnuts, almonds, and flaxseeds -- contain moderate amounts.
• Tomatoes, peppers, and mushrooms -- contain smaller but measurable quantities.

Getting melatonin from food delivers it in physiological doses alongside cofactors, which may be preferable to isolated supplements for general health maintenance.

Timing matters

Melatonin's effectiveness depends heavily on when you take it. For sleep, take it 30-60 minutes before your intended bedtime. Taking it too early can shift your circadian rhythm earlier than desired; taking it too late means it hasn't reached peak levels by the time you want to fall asleep. For circadian rhythm disorders (jet lag, shift work), the timing protocol is different and depends on the direction of the desired shift.