Seasonal Affective Disorder & Our Need for Vitamin D



It's that time of the year again. When the sun sets at 4:30 PM and you wonder why you are increasingly tired and grumpy.

For those of us living in the Northern Hemisphere, this is a common phenomenon. But it can actually be explained scientifically as SAD, or Seasonal Affective Disorder.

The lack of sunlight and early darkness can greatly affect our mood and mental health, affecting some more than others, even interfering with their day to day life.

If you feel more moody, withdrawn, lethargic, or depressed during the winter compared to spring and summer, you may be suffering from SAD. 

What is SAD?

Seasonal Affective Disorder, also known as the "winter blues" is a type of depression that occurs with the change of seasons. It commonly starts around Fall when sunlight exposure starts to decline and can continue until late Spring.

SAD affects up to 2% of Canadians however milder forms can reach up to 15% of the population (1). And the majority are women. In fact, studies show that SAD affects females 4 times as much as males (2).

The increased levels of depression have been associated with reduced natural light exposure and changes in brain chemistry. This is why light therapy is a common treatment of the condition. 


Signs & symptoms

Differentiating between depression and Seasonal Affective Disorder is usually determined by the timing of symptoms. SAD usually affects individuals in the fall months and gets worse during the wintertime. It tends to ease up around spring and summer when there is increased exposure to natural sunlight.

Symptoms of SAD include:

  • depression
  • lack of appetite
  • fatigue
  • irritability
  • apathy
  • lack of focus 
  • sleep problems
  • suicidal thoughts
  • oversleeping
  • decreased sex drive
  • weight gain
  • cravings for carbohydrates and sugars


Risk factors

There are several factors that increase the risk of developing Seasonal Affective Disorder and these include:

  • being female
  • living in the northern hemisphere
  • younger populations
  • having a history of SAD or depression
  • vitamin D deficiency

The importance of Vitamin D

Known as the "sunshine vitamin", vitamin D is a fat-soluble vitamin and hormone that is produced naturally in the skin in response to direct exposure to sunlight. However, this production is greatly diminished during the fall to winter months in certain areas of the world, such as Canada. Deficiency has become quite common in the Northern Hemisphere and among those with darker skin pigments. 

Vitamin D is essential for optimal brain function and mood balance and has been shown to support neural development and cognitive aging in humans (3). Receptors for this vitamin have been found in the brain clearly indicating its importance and influence on this organ. Vitamin D is implicated in the release of neurotransmitters such as dopamine and serotonin which affect brain function and mood states.

Low vitamin D status has been associated with clinical depression and reduced cognitive function (4)(5). SAD patients have been shown to have typically low or deficient levels of this vitamin which usually decreases in the winter months due to decreased sun exposure (6)

Inadequate intake of vitamin-rich foods or lack of exposure to sunlight are the most common causes of poor vitamin D status.

What you can do


Light exposure has been shown to alter the circadian rhythm or the body's natural internal clock by acting as a cue to the brain to synchronize with the outside environment.

Reduced natural light exposure can alter mood states and energy levels and make it harder for individuals to adjust to the shift of the seasons as well as increase the risk of health problems like metabolic and behavioral disorders (7)With the onset of darkness occurring earlier, melatonin may also be produced in excess promoting lethargy and fatigue (8)

Imbalances in neurotransmitters, such as serotonin, have been studied in those suffering from SAD. Therefore, light exposure is a common treatment used to correct these imbalances. 

A lightbox, therefore, can be a great addition to your SAD toolbox to increase your exposure to light via artificial light. This can be incredibly beneficial during the fall and winter months when the sun sets quite early. 

To increase its effectiveness for SAD, Look for a lightbox that reaches 10,000 lux and use for about 20 minutes each day. It is recommended to talk with your health care practitioner before attempting light therapy. 


We all know that exercise is good for us, but it has proven to be a particularly powerful way to fight depression and boost mental health. Exercise has been shown to benefit mental health by increasing feel-good chemicals and endorphins in the brain such as serotonin. 

Any exercise may benefit however, combining aerobic exercise in the outdoors may be one of the most beneficial exercises for improving mental health and SAD (9)


Cognitive Behavioral Therapy 

Any form of counseling can provide tremendous support and relief to an individual suffering from SAD or depression.

CBT, in particular, is a type of psychotherapy that involves various techniques to ultimately change a person's thoughts, emotions, and behaviors to become more positive and solution-oriented. 

It has been shown to outperform light therapy when it comes to long term treatment of SAD and reducing the risk of relapse (10)


Take advantage of sunny days during the wintertime to get some natural sunlight exposure. Not only will this help energize you but it also supports mood. 

Grounding is another practice that can support mental health and anyone can do it. Grounding is the process of reconnecting the body to the electrical currents of the earth which have shown to have positive effects on the body, including improved mood (11) (12). Examples of grounding exercises include walking barefoot, hugging a tree, water submersion, and lying on the ground. 

Vitamin D

Though challenging, you can get vitamin D from some foods such as cod liver oil, mushrooms, organ meats, milk, eggs, oily fish, and soybeans.

Supplementation is usually recommended, however, testing is always a good idea to verify where your levels are at in order to dose appropriately. Choose vitamin D3 and take with a fat to improve absorption (remember vitamin D is a fat-soluble vitamin) or look for a supplement that contains fat in the formula for optimal absorption. 


What you eat has a big impact on your overall health but also on your mental health.  You may find yourself having increased cravings for sugar and carbs during the winter months and when you feel down in order to provide quick relief and comfort. However, this can actually make you feel worse post-consumption and does more damage in the long run by spiking your blood sugar and raising inflammation.

Instead focus on natural whole foods with lean proteins, healthy fats, and fiber-rich carbohydrates to help naturally curb your cravings, increase energy and satiety, and boost brain health.

Particularly beneficial foods for mood-boosting include oats, fatty fish like wild salmon, organic chicken or turkey, dark chocolate, bananas, and berries. 






 Laurence Annez is a Certified Nutritional Practitioner and Health Coach, specializing in PCOS and women's hormones. She also holds a degree in Creative Writing and has extensive experience writing on health and wellness topics. Laurence's
 mission is to inspire and motivate individuals to take control of their own health and reach their ultimate health goals.


Brain healthHealthHealth tipsHealthy eatingLifestyleMental healthMoodNatural healthNutritionSadSeasonal depressionVitamin dWellness