Do You Have Seasonal Affective Disorder? The Science Behind the Winter Blues

Mercey Livingston
Medically Reviewed
March 9, 2020

Feeling blue in the winter months is a common complaint. The lack of sunlight, cold temps, shorter days, and more time spent indoors can be a real downer, especially for those in the northern states. But there is a difference between feeling down about winter and experiencing seasonal affective disorder (SAD), which is a form of depression .

“If you’ve noticed that you've lost the skip in your step that you normally have in those nice, warm summer months, you might be struggling with seasonal affective disorder,” says Kris Romeo , a health coach at Parsley Health.

What is seasonal affective disorder?

SAD is when you feel depressed starting in the fall or winter, but that depression is resolved by spring or summer. “It’s not just a longing for summer and warmer weather, but rather a clinical condition that doctors, like those here at Parsley Health, may diagnose and treat,” Romeo said.

Just because you’ve had SAD before, or think it will resolve soon, doesn’t mean you should delay treatment or seeking help. “The fact that this is so transient makes it harder to identify. One study found that 60% of people who experience winter depression never get treated, likely because it comes and goes before they would seek professional help,” Romeo said.

If you suspect you may be suffering from SAD, keep reading to find out more about the symptoms and how the condition is approached at Parsley Health.

The symptoms of seasonal affective disorder

SAD symptoms can vary from person to person, but in general, the symptoms are similar to depression. SAD is a form of depression, but the distinguishing factor is that it resolves by spring or summer. Again, even though SAD tends to resolve itself over time, you can still benefit from seeking help, especially if it interferes with your daily life.

SAD symptoms can include:

  • Low, depressed mood
  • Loss of interest in things that you were previously interested in, like hobbies
  • Reduced social activity (more prone to stay at home)
  • Fluctuations in appetite (decreased or increased)
  • Fatigue (not wanting to get out of bed or being tired despite getting enough sleep)
  • Insomnia (trouble falling asleep or staying asleep)

What causes seasonal affective disorder?

Besides the colder temps and gloomy weather, what else is behind SAD? This has been studied quite a bit, and it turns out that researchers mainly attribute SAD to lack of light.

“Researchers believe that it is more related to the decrease in light exposure during the winter months than the cold temperature. Light exposure is one of the foundations of health,” Romeo says.

The average American is inside for 99% of the day. When you compare the time spent inside in the winter vs. the summer, you can see how much light influences health.

Light exposure does a lot for our health, but one of the biggest effects it has is on our sleep. And when our sleep is poor it can have a big effect on our mood. One of the major signs of depression is poor sleep, and it is unclear which one is the initial cause, but what is clear is that a cycle often develops where sleep is affected which further affects our mood,” Romeo says.

For this reason, most experts recommend light therapy to help with SAD. The reason light therapy can help is because of the way light exposure helps with sleep, circadian rhythm regulation , and hormone balance.

“When sunlight hits your eyes, it goes to the back of the retina and a signal is transmitted to an area of your brain called the suprachiasmatic nucleus. The result of this signal is the production of a hormone called melanocyte-stimulating hormone, or MSH,” Romeo explains.

MSH is a really important hormone that can help reduce inflammation and can act as an antioxidant, among other things. Because inflammation is linked to depression, finding ways to reduce it can be helpful for mood and brain health. Some other research on light therapy for SAD suggests that it can help with norepinephrine, which is a neurotransmitter that helps you feel motivated and energized—two things that can diminish when you have depression.

Treatments for seasonal affective disorder

Light therapy

Since light and light therapy is promising for treating SAD, how exactly can you get light if you live somewhere that is dark in the winter, or you need to be inside all day for work?

Going outside first thing in the morning to get natural sunlight in your eyes is ideal, but obviously, not the most realistic for many people.

“For those of us who live in darker areas that get less sun, using artificial light from light boxes that can be purchased for home use is a good option,” Romeo says.

There are many different forms of lights you can purchase on the market. Many are labeled “SAD lights” or “light therapy boxes.” If you are unsure about which to purchase, Parsley members can consult their health coach or doctor to find the best options.


As hard as it can be to get out and exercise when you feel depressed, it can be helpful for SAD symptoms. You don’t have to work out intensely or even for that long to reap the benefits, either.

Focus on activities that feel good and enjoyable to you, and keep in mind that exercise can help you release powerful hormones and chemicals that help you feel better. “Exercise increases endorphins, our feel-good neurochemicals. It can also help increase dopamine, which is a neurotransmitter that helps us feel motivation and reward,” Romeo says.

Resolve nutrient deficiencies

Light exposure isn’t the only factor that needs to be addressed when it comes to the winter blues. According to Romeo, it’s a good idea to cover your bases by getting blood work done to check for nutrient deficiencies . One deficiency in particular that can be related to winter blues is iron.

“Iron deficiency, or not having adequate iron stores, can often contribute to depression in general. Make sure that your doctor not only looks at your hemoglobin and hematocrit levels, but also your ferritin level to understand the amount of stored iron you have,” Romeo explains.

You want to make sure your ferritin levels are between 30-200 ng/mL. Anything lower can contribute to a mood issue, especially if you are menstruating, since having a period can make you more prone to losing iron.

“If your labs come back with iron deficiency or lower than optimal ferritin, then your doctor may prescribe an iron supplement to get your levels back to normal levels. There are also a lot of foods that are rich sources of iron, like grass-fed beef, chicken, spinach, oysters, and quinoa,” Romeo says.

If you are vegan or vegetarian, you can still get iron through plant sources, but adding vitamin C to those plants can help your body absorb the iron better.

“This can be done easily by squeezing lemon on your spinach, or eating bell peppers, which are high in vitamin C, with your quinoa,” Romeo says.


Once you see a doctor for SAD, they may suggest that you add some supplements to help with your symptoms and to resolve the root issue that may be behind it. (Don’t forget that it’s important to take supplements that your own doctor or health coach recommends for you.) Here are a few that can be helpful:

  • Tryptophan: “Tryptophan is one of the few supplements that has been studied in SAD. Tryptophan is an amino acid and is the precursor to serotonin which is our happiness hormone,” Romeo says. You’ve probably heard about serotonin when it comes to depression since many pharmaceutical drugs target serotonin (like SSRIs which are serotonin reuptake inhibitors).
  • Omega-3 fatty acids EPA and DHA: Omega-3 fatty acids have been studied for depression and brain health. “The research suggests that EPA may actually be more helpful than DHA, but they likely complement each other. Your doctor will be able to give you a proper dose recommendation, as it is common to underdose omega-3 supplements, which may be why you aren’t seeing results,” Romeo says.

Ready to become a Parsley Health member? Schedule a free call  to learn more about Parsley’s root-cause approach to healing, how to use insurance  to pay for your Parsley medical fees, and more.

Mercey Livingston

Mercey Livingston is a health and wellness writer and certified Integrative Nutrition Health Coach. She is passionate about translating expert and science-based wellness advice into accessible and engaging content. Her work is featured on Well+Good, Women's Health, Business Insider, and among others. When not writing, she enjoys reading, trying out new recipes, and going to new workout classes all over New York City.

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