Seasonal Affective Disorder: What Supplements Should You Take?

Seasonal affective disorder (SAD) is a subtype of major depression disorder that occurs in a seasonal pattern, with symptoms beginning and ending during certain seasons every year. Symptom onset typically occurs in autumn and alleviates in the spring. 

This seasonal pattern is known as winter depression or winter-pattern SAD. However, in some cases, people experience summer-pattern SAD, also called summer depression. This is when symptoms occur during the spring and summer months. 

SAD affects around 4% to 10% of people¹, with females and those between 18 to 30 years more likely to have the condition. It is also more likely to occur in people who have a family history of mental illness, such as bipolar disorder, and those who live far from the equator.

Symptoms of seasonal affective disorder

Because both winter- and summer-pattern SAD are a type of major depression disorder, symptoms of both SAD patterns are similar to major depression. 

Symptoms of winter-pattern SAD include:

• Sleeping more than usual

• Daytime fatigue

• Difficulty concentrating

• Lack of interest in previously enjoyable activities

• Very low mood 

• Intense carbohydrate cravings

• Weight gain

Symptoms of summer-pattern SAD include:

• Irritability

• Agitation

• Trouble sleeping

• Restlessness

• Poor appetite

• Weight loss

• Very low mood

If you think you may be experiencing SAD, it’s important to talk to a healthcare professional about the condition and your options for managing it. 

Causes of SAD

Research suggests that people with SAD have reduced neurotransmitter levels² in the brain, such as serotonin, or they may have difficulties regulating neurotransmitters. Serotonin helps regulate mood, so reduced or dysregulated levels could lead to depression symptoms. 

Below are other potential causes of seasonal affective disorder.

Abnormal melatonin levels

Melatonin, a hormone produced in a gland near the center of the brain, may also play a role in the condition. Melatonin is responsible for regulating sleep. Its levels rise in response to reduced light in the evenings, signaling to the body that it’s time to sleep. 

People with SAD may overproduce melatonin due to the shorter and darker winter days, leading to sluggishness and fatigue. 

Disrupted circadian rhythm

The combination of increased melatonin and reduced serotonin levels may disrupt circadian rhythms. Circadian rhythms are the body’s internal 24-hour “clock.” They respond to light and dark cycles throughout the day and seasonal light patterns throughout the year.

Research has found that circadian rhythms may be timed differently³ in people with SAD, making it difficult for their bodies to adjust to seasonal changes.

Low vitamin D levels

There are links between low vitamin D levels and depression⁴. Vitamin D, also known as the “sunshine vitamin,” is a nutrient the body creates when exposed to the sun. 

As well as being crucial for healthy bones, cell growth, and healthy immune function, vitamin D may help regulate serotonin production⁵. As serotonin helps regulate mood, decreased serotonin production may lead to a depressed mood. 

Most people get the majority of their vitamin D through sun exposure. Less outdoor sunlight exposure in winter may lead to decreased vitamin D levels, impacting serotonin production and contributing to them feeling depressed. 

For people with summer SAD, increased sunlight exposure in summer may interfere with melatonin production, causing irritability and sleeping difficulties. 

Research also suggests that increased pollen counts⁶ in summer may also negatively impact mood. Higher pollen counts can cause allergy flare-ups, leading to inflammation in the body. This inflammation can impact brain function, reducing serotonin levels and leading to a depressed mood.  

How can supplements help?

One treatment option for SAD is dietary supplements, which are manufactured products intended to supplement your diet. They can contain but are not limited to vitamins, minerals, herbs or other botanicals, amino acids, and enzymes. 

As the US Food and Drug Administration (FDA) does not regulate dietary supplements as drugs, they are not assessed for safety and effectiveness before they are marketed. Thus, there are risks involved in taking them. 

It’s important to note that you should take supplements together with other treatment options recommended by your healthcare professional. These could include medications or light therapy, depending on the severity of your symptoms. 

The below contains information that may help you manage SAD symptoms, along with their suggested dosage and possible side effects. 

S-adenosylmethionine (SAMe)

SAMe is a substance naturally produced by the body involved in many processes, including helping to produce hormones and neurotransmitters. SAMe supplements have been available over-the-counter in the US since 1999. 

Low SAMe levels⁷ have been found in people with depression disorders. Because SAMe helps produce several neurotransmitters, SAMe supplementation may help increase serotonin levels in people with depression disorders, helping stabilize mood. 

Research has shown promising results for the effectiveness of SAMe for easing depression symptoms⁸, with doses ranging from 200 to 1600mg/day. 

However, studies with larger samples are needed to provide sufficient evidence for its effectiveness in relieving depression symptoms. 

Potential side effects of SAMe

While SAMe is generally considered safe for most adults, some mild side effects may occur, such as:

• Gastrointestinal issues 

• Dry mouth

• Dizziness

• Insomnia

• Anxiety

• Irritability

Because SAMe is involved in serotonin production, taking it with other supplements and drugs that increase serotonin could lead to serotonin syndrome, a serious condition characterized by confusion, sweating, muscle stiffness, and abnormal heartbeat.

SAMe could also interact with other supplements or medications you may be taking, causing symptoms similar to serotonin syndrome. 

If you are taking any medicines in the following categories, be sure to consult your healthcare provider before taking SAMe supplements. 

• Antidepressants

• Amphetamines

• St. John’s Wort

• Narcotics

• Dextromethorphan

You should not take SAMe if you have bipolar disorder, as it could increase symptoms of mania. Additionally, avoid taking SAMe if you are pregnant or breastfeeding since there is no evidence whether it is safe to take in these cases. 

St. John’s Wort

St. John’s Wort is a flowering plant native to Europe and Asia. For centuries, people have used extracts from this plant to treat various conditions, including depression. It is an over-the-counter supplement available from pharmacies and health food stores.

The plant’s active ingredients may help increase neurotransmitters in the brain, such as serotonin, helping regulate mood. 

Research has shown that St. John’s Wort extract is as effective as SSRIs⁹, a type of antidepressant medication, for treating mild to moderate depression. It also has fewer side effects than SSRI medication.

Potential side effects of St. John’s Wort

Some people may experience the following symptoms. 

• Fatigue

• Gastrointestinal issues

• Insomnia

• Skin rashes

• Irritability 

• Sunlight sensitivity

St. John’s Wort also interferes with several medications and can reduce their effectiveness, including: 

• Antidepressants

• Birth control pills

• Some HIV medications

• Some heart medications

• Some cancer medications

• Cyclosporine

• Warfarin

• Some statin medications

It is not considered safe to take St. John’s Wort if you are pregnant or breastfeeding. 

Vitamin D

While it’s often absorbed through diet and sunlight exposure, you can also get vitamin D as a dietary supplement. Supplement forms are available over-the-counter from pharmacies and health food stores and may also be prescribed by your doctor. 

Research has shown that vitamin D could be a contributing factor in SAD¹⁰, as vitamin D levels in the body fluctuate throughout the year in relation to seasonal sunlight exposure. 

As vitamin D helps produce serotonin, lower levels in winter could contribute to SAD symptoms. 

Current studies have not been able to say whether supplementing with vitamin D directly improves SAD symptoms. Still, some signs suggest sufficient vitamin D levels are important for overall well-being¹¹. 

The National Institute of Health suggests an average intake of 400 to 800 IU (15 to 20 mcg) of vitamin D per day for adults. 

Discuss your supplement use with your healthcare provider to ensure that your intake is sufficient for your daily requirements. 

N-acetylcysteine (NAC)

NAC is an FDA-approved drug used to treat various conditions. It is available from healthcare providers and as an over-the-counter supplement in pharmacies and health food stores. 

NAC can help prevent cell damage¹² and reduce inflammation¹³ in the brain, which may help lift feelings of depression. 

Studies have shown that NAC helps improve depressed mood in people with depression disorders, so it may also help improve depressed mood in people with SAD. 

It is available in capsules and tablets ranging from 500 to 1000mg and is considered safe when taken in these amounts. Higher dosages can cause side effects such as nausea, vomiting, diarrhea, and constipation. 

If you are taking blood-thinning medications or have a blood clotting condition, do not take NAC, as it can prevent blood clotting. Additionally, if you are pregnant or breastfeeding, it is not recommended to take NAC. 

The lowdown

SAD is a depression disorder related to seasonal changes that may trigger reduced or dysregulated neurotransmitter levels, leading to mood changes and disrupted sleep-wake cycles. 

Supplements may help manage SAD symptoms by helping regulate hormone and neurotransmitter levels. There are risks involved in taking supplements, so it’s important to talk to your healthcare provider if you are considering taking them.