The Hormonal Link to Seasonal Affective Disorder (SAD) & Why It Develops in Winter

As the days get shorter and colder in the fall and winter months, many people start to experience symptoms of low mood, fatigue, changes in appetite and sleep, and a lack of interest in normal activities. This condition is known as seasonal affective disorder (SAD) and it impacts many adults. SAD is considered a type of depression that recurs during a particular season each year.

What causes this seasonal pattern of depression and what role do our hormones play? Let’s take a closer look.

Seasonal Affective Disorder blog image with an illustration of a sad woman under a rain cloud

Is Seasonal Affective Disorder Caused By a Lack of Sunlight?

The main driver of SAD is believed to be the shortening daylight hours during fall and winter. Exposure to sunlight helps regulate our circadian rhythms and internal body clock. When we get less natural light exposure, it disrupts our circadian rhythms, which can lead to feelings of depression. Exposure to sunlight also causes our bodies to produce vitamin D, so lower sunlight in winter means lower vitamin D levels, which has also been linked to depressive symptoms.

The Hormones That May Affect Your Seasonal Depression

In addition to reduced sunlight, there are several key hormones that fluctuate across seasons and may contribute to SAD:


This hormone regulates sleep and is produced in the dark. As nights get longer in the winter, more melatonin is produced, which can lead to symptoms of excessive sleepiness and lethargy.


Our serotonin levels seem to follow seasonal patterns, with lower levels in the winter. Reduced serotonin is strongly linked to depression and anxiety. Sunlight exposure boosts serotonin production.


Like serotonin, dopamine also drops in the winter months. Dopamine is key for motivation, focus, and feelings of pleasure or reward. Lower dopamine leads to winter’s typical lack of motivation and difficulty feeling happy.

Vitamin D

This critical vitamin is produced by the skin when exposed to UV rays in sunlight. Vitamin D maintains a balanced mood and healthy bones, but deficient levels are common in winter, contributing to seasonal depression.


Changes in estrogen levels in winter have been observed in women with SAD, but the implications are complex. Estrogen modulates serotonin production, so its seasonal decrease may exacerbate low serotonin’s effects in winter.

The hypothalamic-pituitary-adrenal axis – This critical hormonal system manages our stress response. Dysfunction of the HPA axis is common in many mood disorders. Changes in circadian rhythms from reduced sunlight may dysregulate the HPA axis.

The research supports that our major hormone systems are influenced by seasonal changes, especially sunlight exposure. The biochemical effects of hormones like serotonin, dopamine, melatonin, estrogen, cortisol, and vitamin D levels seem to play a significant role in why our mood and behavior change during fall and winter.

What Can You Do To Manage These Seasonal Hormone Shifts?

Here are some tips:

  • Get outside in daylight when possible
  • Exercise regularly to boost serotonin, dopamine, and endorphins
  • Take vitamin D supplements to maintain healthy levels
  • Be aware of oversleeping and maintain a consistent sleep schedule
  • Eat a healthy diet high in fruits, vegetables, and whole grains
  • Try to limit sugar and processed foods that can worsen mood
  • See a doctor or mental health professional if depression persists

The recurrent pattern of SAD during the darker months is our body’s way of responding to shorter daylight exposure and the subsequent impact on our hormones. Targeted use of light therapy, vitamin D, exercise, sleep regulation, and professional treatment can help manage seasonal changes in hormones and mood. With some awareness and proactive steps, we can alleviate some of the distress of SAD and continue enjoying life throughout the winter.

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