What Are The Causes Of Seasonal Affective Disorder?

Causes of seasonal affective disorder

Do you get the winter blues? You’re not the only one. Each year, roughly 5 percent of the country deals with seasonal affective disorder, or SAD. This form of depression develops in the winter and goes away come spring.1

Symptoms of winter SAD include sadness, low energy levels, sleepiness, overeating, weight gain, and social withdrawal.2 It can also last for about 40 percent of the year.3


To treat SAD, it’s good to know how it develops. Here are the three major causes of seasonal affective disorder.

1. Low Vitamin D

Seasonal affective disorder caused due to low vitamin D


Seasonal affective disorder is often caused by low vitamin D levels. But unlike most nutrients, deficiency has nothing to do with diet. It’s actually related to sunlight.

Sun exposure helps your skin make vitamin D. Specifically, ultraviolet-B radiation is needed to convert it from 7-dehydrocholesterol.4 However, this vitamin isn’t naturally available in most foods, so you need to get enough sun. Vitamin D is also needed for normal brain function. It’s linked to higher levels of dopamine and serotonin, two neurotransmitters that control your mood.5 6


During the winter, there is less sunlight. The days are shorter and the nights are longer. Plus, the cold might make you want to stay indoors! You’ll be less likely to soak up enough sun to make vitamin D.

It explains why SAD is more common in places that don’t get a lot of sunlight.7 To boost your intake, consider vitamin D supplements. You can also get some vitamin D from salmon, tuna, beef liver, fortified orange juice, milk, and cereal.8


2. Low Estradiol Levels

Seasonal affective disorder caused due to hormonal change

The primary sex hormone in females is estradiol. If levels are low, depressive symptoms can crop up.9


Interestingly enough, a large Norwegian study found that estradiol levels change with the seasons. It reaches its peak in June. Come October, it reaches an all-time low. The changes were small, yet noteworthy.10

These findings might explain why SAD is four times more likely to affect women than men. The risk also increases if you already struggle with bipolar disorder, depression, or have a family history of depression.11


3. Circadian Rhythm Disruption

Seasonal affective disorder caused due to disrupted sleep cycle

Winter’s extra dose of darkness can also lead to SAD. At night, your brain naturally releases melatonin to promote drowsiness. This is part of your normal circadian rhythm or body clock.


The long nights can disrupt this process. Melatonin production increases, but in some people, it might go too far. The result is a delayed circadian rhythm and yawning – lots of it.12

If you already have depression or low vitamin D levels, this disturbance might boost your SAD risk. You also might be prone to melatonin-induced disruptions if you work at night or travel often.