Melatonin says, “It’s dark”.

Melatonin is a hormone produced by the pineal gland, a small group of specialized cells in the brain, just behind the eyes. The retina communicates light information to these cells. Melatonin is released into the brain and bloodstream in response to the level of ambient light—low melatonin during the day and high melatonin at night. Telling the body that it’s dark outside is particularly important for organisms as day length changes with the season. 

Typically, melatonin secretion starts to rise around 4:00-6:00 p.m., peaks around 12:00-2:00 a.m., then starts to decline between 4:00-6:00 a.m. This pattern facilitates sleep onset around 10:00 p.m.-2:00 a.m., and waking around 6:00-8:00 a.m. However, this healthful pattern is disrupted when we use certain types of light at night (see below). To learn why this pattern of melatonin secretion is particularly healthful, read our article “Sleep and Biological Clocks”.

Melatonin secretion changes as we age

Melatonin secretion changes throughout life. Particularly after age 60, people tend to fall asleep earlier, wake earlier, and sleep less deeply. This happens because the total amount of secreted melatonin declines with increasing age. Also, the peak concentration of melatonin secreted is lower and occurs earlier in the evening as a person gets older.^1–3 (And there you have it: the biological basis for the “early bird” dinner buffet.) 

Non-sleep benefits of melatonin

As an added bonus, melatonin is also an antioxidant. It directly scavenges free radicals,^4,5 which damage vital molecules like DNA in the cell. In fact, one melatonin molecule is predicted to have 13X the antioxidant capacity as vitamin C. This is because melatonin’s breakdown products (metabolites) also act as antioxidants. 

Another non-sleep benefit of melatonin is that it affects gene expression in cells throughout the body. Specifically, melatonin activates gene expression of antioxidant enzymes and inhibits gene expression of molecules that may promote cancer in susceptible individuals, such as insulin, estrogen receptor, and many enzymes.^6–11

Artificial light at night inhibits melatonin

As discussed, the retina tells the pineal gland how much light is in the immediate environment. When the retina senses light, the pineal gland slows the production of melatonin. The brighter the light, the less melatonin is created. Importantly, the actual time of day or night doesn’t matter; it only matters that your retina is sensing light. This means that at night, the light from your phone, tablet, TV, lamp, and streetlights can all inhibit melatonin production. 

Low levels of melatonin make it harder to fall asleep. In fact, the use of screen devices (tablets, smartphones) around bedtime is significantly associated with insomnia, poor sleep quality, and daytime fatigue in adults.¹² From the time you turn off your device (and all other sources of ambient light), it takes approximately 2 hours for melatonin to reach its peak.¹³ And once you finally fall asleep, you get less total melatonin and less total sleep than had you not used your device before bed. Less sleep means that you are sleep-deprived, which has serious mental and physical consequences.

Less melatonin also means that you miss out on the non-sleep benefits of melatonin described earlier. What’s more, some research implicates a link between sleep disruption by light at night and breast cancer in humans.^14–16 The connection between breast cancer and melatonin is suggested by the multiple ways in which melatonin inhibits estrogen signaling.¹⁷

Preserve your melatonin with warm light

However, there is good news! It turns out that melatonin is especially sensitive to a specific type of light, and you can preserve your melatonin levels if you minimize that light around bedtime. The type of light that melatonin is sensitive to is so-called “blue” light, which is typically emitted from LED screens on smartphones, tablets, and TVs.¹⁸ The “blueness” of light just refers to a quality of light and usually doesn’t appear to be the color blue. 

You can minimize blue light from your devices by increasing the “warmness” of light through the device display settings. Importantly, increasing the warmness of light on devices has been shown to preserve melatonin levels at night and promote a better night’s sleep.¹⁹ So set that feature to occur automatically at sunset on your device! If you want to be very safe, you can wear amber-colored (blue-blocking) glasses at night, which have been shown clinically to improve sleep^20,21 and to make you look super cool.