As the days grow shorter and temperatures drop, many people experience a noticeable shift in their mood and energy levels. For some, this seasonal change goes beyond the typical "winter blues" and can lead to a form of depression known as Seasonal Affective Disorder (SAD). If you're noticing feelings of sadness, fatigue, or withdrawal during specific times of the year, particularly in the colder months, it's important to understand what SAD is and how it can be managed.

What is Seasonal Affective Disorder (SAD)?
Seasonal Affective Disorder is a type of depression that occurs at the same time each year, most often in the fall and winter. It is thought to be triggered by the reduced levels of sunlight, which disrupt our body’s internal clock, leading to changes in mood, energy, and sleep patterns. Though SAD is most commonly associated with winter, some people experience it in the spring or summer, but this is less common.
Symptoms of Seasonal Affective Disorder
The symptoms of SAD typically begin in late fall or early winter and may last until spring or early summer. Common symptoms include:
Persistent low mood
Fatigue and low energy
Sleep disturbances: Oversleeping is common in winter-related SAD, while insomnia may occur in the summer form.
Changes in appetite: Craving carbohydrates and overeating.
Difficulty concentrating
Social withdrawal
Loss of interest in activities you normally enjoy
While the winter months are the most common time for SAD, people with summer-onset SAD may experience agitation, restlessness, weight loss, and difficulty sleeping.
Treatment Options for Seasonal Affective Disorder
SAD is treatable. There are many theoretical treatments for SAD. Listed here are the most common ones. Some are more effective than others and unfortunately, in many cases, the studies in these treatments are often small and limited in number. But we do our best with what we have.
1. Light Therapy (Phototherapy)
Light therapy is one of the most common and effective treatments for SAD. It involves sitting near a specially designed lightbox that emits bright, artificial light that mimics natural sunlight. This treatment option is fairly well studied. According to one meta-analysis (a study of studies) it was found that light between 1000-5000 lumens in the morning was most optimal for reducing SAD and improving energy. It's best to use the light early in the morning. According to the study, lumen levels outside of this range are less effective. The study recommends using one of these lights for no more than an hour per day but that hour can be split in two parts (two half hour blocks) and used in the afternoon as well, if you feel tired in the afternoon.
Bright light therapy reduced depression scores by 37% more than the dim light placebo. In these studies, bright light was defined as >1000 lumens.
There are potential side effects to light therapy. Mild burning, nausea, headache, eye fatigue, phototoxicity, itching and redness of the skin are possible with light therapy. In general, many of these side effects can be greatly reduced or removed by using UV free lights. Rare side effects include mania or hypomania in people with bipolar disorder. If the lamp emits UV light, skin cancer risk may increase with long term use. It is a good idea to talk to your health care provider before trying bright light therapy.
2. Cognitive Behavioral Therapy (CBT)
Cognitive Behavioral Therapy (CBT) is a structured form of talk therapy that helps individuals identify and change negative thought patterns and behaviors. It has been shown to be effective for managing depression and can be tailored specifically for SAD.
CBT for SAD focuses on changing negative responses to the winter season and developing coping strategies to prevent relapse in future seasons. CBT was found in one study to be as effective as bright light therapy when they were both used for 6 weeks. The study followed up after 1 and 2 years and the CBT group was less likely to suffer relapses than the light therapy group. To be fair, bright light therapy is not expected to be effective years after using it for 6 weeks, but the point they were trying to make was that CBT benefits patients longer than bright light therapy.
CBT was found to get people to remission a little faster than light therapy in another study. While this really small study is suggesting you get better effects when the two treatments are combined. The study was really tiny though so we need more data to know for certain.
3. Medication and Herbal Medicines
Some herbal medicines would likely benefit SAD. Which herbs are likely to work for an individual is largely based on their individual needs. Some herbs, like St. Johns Wort, will interfere with other medications. Many of the antidepressant herbs interact in dangerous ways with depression and anxiety medication so it is very important to consult a qualified professional before adding herbals if you are on medication. Gentle options that are not know to interfere with medications do exist.
For some individuals, antidepressant medication may be necessary, particularly if symptoms are severe or don’t respond to light therapy or other treatment options. Selective serotonin reuptake inhibitors are commonly prescribed to treat SAD. These medications are outside of my scope of practice so I cannot prescribe them but your family doctor or even a walk in clinic might help you with a prescription.
4. Vitamin D Supplements Might Not be the Answer
Vitamin D levels tend to be lower in people who experience SAD, so taking a vitamin D supplement seems like it should improve mood, but we have to be careful with this assumption. Vitamin D is found to be lower in a lot of conditions and supplementation does not always improve those conditions. We need good randomized controlled trials to know if vitamin D supplementation will help. There are a lot of studies in vitamin D for SAD but the results are very inconsistent.
A very large study that gave a reasonable dose (2000 IU) of vitamin D3 for 5.7 years did not find any improvements in mood or depression scores. There is a confounding factor in this study because the vitamin D group was also given fish oil. There were 18 353 people in the study and big studies are usually more reliable than small ones. I think we can conclude that vitamin D and fish oil together at the doses used do not reduce depressive symptoms. Another study confirmed these results at very high doses once per month for 6 months. No improvement in depression was observed.
A few very small studies found high doses of vitamin D improved depression scores in patients with SAD but the studies were too small to form any conclusions, especially given the contradictory results from larger study.
One study, did find a dose-response relationship and these relationships make us trust a relationship exists between vitamin D supplementation and SAD symptoms a bit more than other results, but the study was still pretty small.
So, what does all this mean? Vitamin D supplementation at typical dosing of 2000 IU per day and at high, infrequent dosing, doesn’t seem to improve depressive symptoms, at least not consistently. High doses of vitamin D carry a risk of toxicity which might make the option not worth the risk. Some small studies show possible improvements in wellbeing but the evidence is fairly weak. Vitamin D may be good to take for other reasons but it would not be a first choice for improving SAD.
20 minutes of sunlight per day provides 50-90% of our vitamin D needs, it is possible vitamin D is lower in people with SAD because they go outside less.
5. Exercise and Physical Activity
Regular exercise, particularly outdoor activities, can boost endorphins, serotonin levels and vitamin D production, improving mood and reducing symptoms of depression. Exercise is an effective, well studied treatment for regular, non-seasonal depression. There is less research in SAD specifically.
One study compared 1 hour of cycling exercise per day to 2 hours of bright light therapy per day and a placebo group. Compared to the placebo group, both the light therapy and the exercise groups saw a decrease in depression symptoms in the winter. The exercise group saw a reduction in depression scores by 68.5% and the bright light therapy group saw a reduction of 64.5%. The difference between these two was not deemed significant. The placebo group saw a reduction of depression symptoms by about 5%. This small study was only a week long so more research is needed, but it is a helpful study because it shows us both these treatments can work very quickly.
Another study found that people who exercised in bright light, for example, outside, were less likely to experience SAD than people who exercised in low light.
6. What about Nutrition?
The research on the effect of nutrition on SAD is very lacking at the moment. Some correlations between diet and SAD have been observed but there are too many confounding factors in those studies to know if one causes the other. or the other way around.
We know that people with SAD tend to eat more carbohydrate rich foods. This does not mean that carbohydrates cause SAD, it might just mean that people with SAD find relief from carbohydrates. There is a very old study that showed people with SAD, when given high carbohydrate meals saw a decrease in tension, depression and anger. When given high protein diets, the subjects had more tension, depression and anger. Very old studies should be taken with a grain of salt as research methods are better now.
Unfortunately, the newer studies are even less clear with some studies reporting better improvements with carbohydrate supplements over protein-carb combination supplements and others reporting better improvements with protein drinks than carbohydrate drinks. I suspect there is some product bias in these studies making them less trustworthy.
Seeking Professional Help
If you suspect you have SAD and self-care strategies aren’t providing enough relief, it’s important to consult with a healthcare provider or mental health professional for a proper diagnosis and treatment plan that works for you. This can be accessed a number of ways but the easiest is likely by calling 811 where they can match you to appropriate services. I also happen to know a lot of registered counsellors and would be happy to help you find a good match.
TLDR
While Seasonal Affective Disorder can make the colder months feel challenging, it's a condition that can be managed with the right treatment and lifestyle adjustments. If you struggle with SAD or winter blues, remember that there are effective options for managing it, including light therapy, cognitive behavioral therapy, medication, and possibly exercise. By taking action early, you can reduce the impact of SAD and regain control of your mental health during the changing seasons.
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