Taking Vitamin D For Seasonal Affective Disorder: All You Need To Know

Have you considered clinical trials for Seasonal affective disorder (SAD)?

We make it easy for you to participate in a clinical trial for Seasonal affective disorder (SAD), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

What is seasonal affective disorder?

Seasonal affective disorder (SAD) is described as depressive episodes occurring at the same time each year, predominantly in the winter or autumn season, with symptoms easing at other times of the year. 

A person might experience “the blues” or a more depressed mood as the colder winter season, with shorter days, begins. Improvement in mood returns with the warmer seasons and longer days. 

It can occur at other times of the year, however, it is much less common outside the autumn and winter seasons.

Vitamin D is known to play a role in SAD since the condition mainly occurs when people have less exposure to the sun, often resulting in a vitamin D deficiency. 

SAD is a common type of depression, affecting 11%¹ of people with seasonal bouts of major depression

It’s classified as a serious mental health issue since it can significantly affect a person’s behaviors, daily functioning, and relationships with others. It’s a complex disorder likely influenced by several factors. 

Early treatment can reduce the chances of the disorder becoming worse and can help to improve your quality of life. 

What causes seasonal affective disorder?

The exact cause of SAD has not been established. However, triggers may include changes in sunlight in different seasons, disruptions in the natural sleep-wake cycles (called the circadian rhythm), decreased serotonin levels, and excess melatonin

Low vitamin D levels² have been linked to depression, low mood, and an increased likelihood of SAD. Vitamin D levels tend to be lower in the winter months³ when the condition is prevalent due to a lack of sunlight. 

Light therapy is often used for people with SAD to increase their vitamin D levels. Based on these observations, some researchers believe that vitamin D may play a role in reducing symptoms of SAD. However, the evidence is still inconclusive⁴.

Who is affected by seasonal affective disorder?

Because of its connection to the seasons, SAD was thought to be linked to climate, sunlight hours, and temperature. 

This theory would have stronger support if more people living in northern countries were affected.

Regardless, studies have shown that SAD affects around 0.4% of the US population⁵ and 2.9% of people in Canada¹. Women⁶ are significantly more likely to be affected than men, with a 4:1 ratio. 


DSM-5 criteria is used to classify psychological disorders. It includes symptoms and descriptions used by clinicians as a common language for diagnosis. 

To be diagnosed with SAD, a person must have a total remission in summer, which means symptoms are significantly reduced or not present at all. 

It can be distinguished from other depressive disorders such as major depressive disorder, where the symptoms last all year round but may just worsen during winter. 

Symptoms of seasonal affective disorder

People suffering from SAD generally present with typical symptoms of depression. These include: 

  • A decrease in pleasure or interest in activities

  • Social withdrawal

  • Reduced energy

  • A sense of worthlessness or hopelessness

  • Difficulty concentrating

  • Repeated thoughts of death or dying

  • Indecisiveness

  • Feelings of guilt

Less typical symptoms include:

  • Increased appetite, binge eating, or carbohydrate cravings

  • Weight gain 

  • Feeling sluggish or increasingly tired

  • Hypersomnia (sleepiness)

  • Decreased appetite

How does vitamin D help with seasonal affective disorder?

Vitamin D deficiency is linked to the development of depression.

One study⁷ has shown that supplementation with 5,000 IU (international units) of vitamin D per day during winter significantly reduced symptoms of SAD in women. 

However, another study⁸ did not find any relief from symptoms with vitamin D supplementation. 

Although the evidence isn’t clear, vitamin D could likely help improve mood during SAD

Another reason for vitamin D deficiency is that people more often wear sun protection when outside to protect themselves from conditions such as skin cancer and premature aging. 

Vitamin D function and its effect on mood

Vitamin D is a hormone made by the body or ingested as a nutrient. It has many health benefits and is essential for multiple bodily functions and brain processes.

Vitamin D can be produced by the body when skin is exposed to UVB rays from the sun or light therapy, and you can also get it by eating particular foods.

Vitamin D3 (cholecalciferol) is the form of vitamin D produced in the body and obtained from foods such as oily fish, dairy, meat, mushrooms, leafy green vegetables, and other vitamin D fortified foods. 

Although vitamin D is generally known for its benefits in bone protection, it plays an important role in maintaining overall well-being and happiness. 

Vitamin D regulates serotonin, an important neurotransmitter for mood, feelings of happiness, and positive emotions. Therefore, the decreased vitamin D levels during winter may be responsible for reduced serotonin activity. 

Serotonin is also required for melatonin production, which regulates sleep-wake cycles often disrupted in people with SAD. This means that having good vitamin D levels in the body may help with emotional brain circuitry, controlling sleep patterns, and reducing symptoms of depression. 

Treatment using vitamin D

Vitamin D supplements

Research suggests vitamin D⁹ supplements may help to relieve symptoms of SAD. Furthermore, vitamin D intake during other seasons could help prevent the onset of depression symptoms during winter since vitamin D is stored in the body. 

You can purchase vitamins over the counter or take vitamin D supplements prescribed by a clinician. 

These supplements are in the form of a fat-soluble vitamin D. This means that the supplements should be taken with a large meal so that the body can more efficiently absorb the vitamin D. 

You should consult your doctor about the correct dosage to reduce depression symptoms and have them carefully monitor you during treatment. 

Getting vitamin D from your diet

You can increase your vitamin D intake by eating more foods rich in this vitamin. Examples of foods high in vitamin D include:

  • Fish liver oils, e.g., Cod liver oil 

  • Edible wild mushrooms

  • Wild salmon

  • Mackerel (raw)

  • Herring (raw)

  • Mushrooms (white button)

  • Raw egg yolk

Other sources:

  • Farmed salmon

  • Meat

  • Fish and shellfish

  • Dairy products

  • Fortified breakfast cereals

Getting vitamin D from food sources means you can overcome a lack of sunlight during specific times of the year. This also applies to people living in countries where sunlight is less available and daylight hours are very short in the winter. 

It is important to note that concentrations of vitamin D in foods can vary significantly and often depend on the type, whether it was farmed or wild, and the location where it was sourced. 

However, the vitamin D content in most foods is very low, with the exception of some fish liver oils and fatty fish, especially compared to what you can obtain from sun exposure or supplementation. 

In addition, absorption of vitamin D differs between people. 

Sun exposure

Spending more time outside during the winter months could be very beneficial for people with SAD. In addition, ensuring that you have adequate exposure during the summer months may help to increase serum vitamin D levels in preparation for the winter. 

Studies¹⁰ have shown that activities that exposed people to natural sunlight resulted in better mood, increased self-esteem, happiness, and reduced depression symptoms

In one case, these included a 20-minute walk outside five days per week or even exercising outdoors instead of inside. 

It is extremely important, of course, that you take care not to expose yourself to excessive amounts of UV rays because overexposure causes damage to the skin that can result in complications such as skin cancer and premature aging. 

Alternative treatments

Several other beneficial treatments are available:

The lowdown

SAD occurs predominantly in winter when vitamin D levels in the body are low. Some studies suggest that increasing vitamin D through diet or sunlight exposure may reduce the likelihood of depression symptoms developing.

It’s always advised to seek help from a medical or mental health professional when experiencing any depressive symptoms.

It’s important to be clear when consulting your doctor to describe whether the symptoms are worse or occur only during particular times of the year. This information will help lead to a correct diagnosis and determine whether vitamin D supplementation could be helpful.

Have you considered clinical trials for Seasonal affective disorder (SAD)?

We make it easy for you to participate in a clinical trial for Seasonal affective disorder (SAD), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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