Melatonin And Seasonal Affective Disorder: How Is It Linked?

Melatonin is a hormone produced by your brain that regulates your body’s sleep-wake cycle. Your brain naturally starts to produce melatonin about two hours before you sleep, causing you to feel tired. 

People who suffer from seasonal affective disorder (SAD) may overproduce melatonin, causing them to feel sleepy during the day. This is common for people who experience SAD in the winter. 

A small number of people experience SAD in the summer which often causes them to have difficulty sleeping. Melatonin supplementation may help with this condition.

What is seasonal affective disorder?

Seasonal affective disorder is commonly known as seasonal depression or the “winter blues.” It is a subtype of major depression that occurs due to changes in climate and seasonal weather. 

Symptoms of SAD last for approximately 40% of the year,¹ with full recovery for the remainder of the year.​​ To be diagnosed with seasonal affective disorder, you must have experienced depressive symptoms during the specific season for at least two consecutive years. 

Common symptoms of SAD include: 

• Feeling sad or depressed

• Difficulty concentrating 

• Tiredness 

• Increased appetite, particularly for carbohydrates 

• Lethargic and lacking in energy

• Difficulty making decisions 

• Social withdrawal

About 5% of people¹ in the US are diagnosed with seasonal affective disorder. 

The people most at risk of developing SAD² include females, those aged between 18-30, and those who have a family history of seasonal depression. 

Living far away from the equator can also contribute to the development of SAD as countries further from the equator receive fewer hours of sunlight. 

Seasonal affective disorder is most commonly experienced in fall and winter. However, approximately 10% of people diagnosed with SAD experience symptoms during summer.³ 

Depressive symptoms of seasonal affective disorder tend to vary depending on the season. Those who experience SAD in the winter are more likely to have atypical depressive symptoms,⁴ such as an increased need for sleep and weight gain. On the other hand, those who experience SAD in the summer tend to have typical depressive symptoms, such as weight loss and reduced sleep.

How does melatonin affect seasonal affective disorder? 

Seasonal affective disorder is directly correlated with increased levels of melatonin. Melatonin is the hormone that regulates your sleep cycle. Melatonin production is inhibited by light and stimulated by darkness. This means that the melatonin levels in your bloodstream should be low during the day and high at night. 

In the evening, when the sunlight is reducing, the cells in your eyes sense that it is getting dark and send a signal to a structure in your brain called the suprachiasmatic nucleus (SCN). 

The SCN is responsible for controlling your biological clock and stimulates melatonin production when it receives this signal from your eyes. 

The SCN then tells the pineal gland in your brain to produce melatonin, which is released into your bloodstream, causing you to feel sleepy. 

Melatonin levels in your bloodstream should start to increase about two hours⁵ before you go to sleep, and peak about three hours after you fall asleep. 

When you wake up in the morning, your melatonin levels should then drop due to the presence of both sunlight and artificial light. 

Excess melatonin does not cause seasonal affective disorder, but it can cause atypical depressive symptoms, such as increased tiredness or sleepiness, especially during the winter.

During the winter, there is less sunlight, so the days and shorter and darker. This may cause the SCN to stimulate the pineal gland to producemelatonin even during the day, resulting in an overproduction of melatonin. This can cause you to feel sleepy during the day, even if you had enough sleep the night before. 

Can melatonin help with seasonal affective disorder? 

Not everyone with SAD experiences increased sleepiness. Some people, especially those who experience SAD in the summer, suffer typical depressive symptoms and struggle to fall asleep, causing tiredness during the day. 

If you struggle to sleep during a SAD episode, consider talking to your doctor about taking melatonin supplements. 

Research has shown⁵ that melatonin can synchronize your circadian rhythm (biological clock) and improve both sleep onset and duration of sleep. 

Another way to optimize your melatonin production is light therapy. As light suppresses melatonin production, light therapy is a first-line treatment for seasonal affective disorder. Light therapy helps to reduce melatonin production in the morning and boost your mood.

Sleep hygiene tips to manage seasonal affective disorder

You may also benefit from these sleep hygiene tips to improve your melatonin production and sleep quality. 

Keep a regular sleep schedule

Going to bed and waking up at the same time each day will help to regulate your internal biological clock by encouraging your body to produce melatonin at the correct time. This helps you to feel tired when you need to go to sleep.

Keep your room dark at night

Make sure your curtains block out any outside light. Complete darkness will help your brain produce melatonin as efficiently as possible. 

Avoid using electronic devices before bed

Light inhibits melatonin production, especially blue light such as the light from phones and laptop screens, making it difficult to fall asleep. 

If you have electronic devices in your room, like laptops, phones, or gaming consoles that have lights when charging or left on, turn these off completely or remove them from your room when you are going to sleep. 

Your body should start producing melatonin two hours before bedtime, so try to avoid using devices during this time. If you do use electronic devices before bed, turn on the blue light filter feature that most devices have. 

Create a relaxing evening routine

Having a relaxing evening routine helps to calm your mind and body, making it easier to fall asleep. You may find that taking a warm bath or shower or spending half an hour reading helps you to relax before bedtime. 

Whatever you choose to do before bedtime, make sure it is something you enjoy as this will make it easier for you to create a routine. 

Avoid caffeine before bedtime

Consuming food and beverages containing caffeine right before bedtime can make it difficult for you to fall and stay asleep.

Caffeine-containing foods and beverages include:

• Coffee 

• Chocolate 

• Energy drinks 

• Some chewing gums 

• Cola 

Avoid vigorous exercise before sleep

Vigorous exercise, like heavy weight lifting or cardio, may cause difficulty falling asleep. If you like to move your body before you sleep, try gentle movement in the form of meditation or yoga. 

Keep your room fresh

Airing out your room during the day to keep your room smelling fresh and clean can help improve your sleep. You should also wash your sheets and remove any dirty laundry regularly.

The lowdown

Seasonal affective disorder that is experienced in winter is directly associated with excess melatonin production. This causes sleepiness and fatigue, even when you have had enough sleep. Treating SAD symptoms that are caused by an excess of melatonin involves temporarily inhibiting melatonin production.

A small percentage of patients diagnosed with SAD experience depressive symptoms during the summer. In this situation, it is common to have difficulty falling or staying asleep. Melatonin supplementation or improved sleep hygiene may help to increase levels of melatonin in the bloodstream, aiding sleep and reducing depressive symptoms.