Experts are still researching what causes SAD, but findings so far suggest there may be multiple neurobiological factors, including the following.

• Pineal gland disruption: Sunlight detected by the retina of the eye sends signals to the more primitive parts of the brain, one of which is the pineal gland. The pineal gland plays a vital role in hormone regulation, and one of the hormones it controls is melatonin. Disruption of the pineal gland hormone axis due to light deprivation is thought to be a primary cause of SAD. Support for this line of thought comes from several observations. First, SAD is decidedly more common in parts of the world that are more deprived of sunlight. In the U.S., for example, the rate of SAD is much highest in Alaska and is higher in the Pacific Northwest and in Maine than in southern states. The rate of SAD is higher in Scandinavian countries than in southern European countries. Second, people with SAD who travel to a more southern location experience improvement in their symptoms.
• Melatonin disruption: Melatonin helps set the body’s biorhythms. According to a 2015 overview of SAD in Depression Research and Treatment, people with SAD may produce abnormally high levels of melatonin, which drains energy and provokes sleepiness.
• Serotonin regulation problems: Research shows that people with SAD have trouble regulating serotonin, a “feel-good” neurotransmitter that is believed to be involved in mood control. A 2014 study in European Neuropsychopharmacology found that people with SAD have seasonal fluctuations in SERT, a protein that is involved in serotonin transport. In the winter months, they have 5% more SERT, which translates into lower serotonin activity, which is believed to be related to depression.
• Reduced vitamin D levels: During the winter months, when sunshine is in shorter supply, people with SAD may produce less of this important vitamin. Having low levels of vitamin D, which is known as the “sunshine vitamin,” has been linked to depression and bipolar disorder. Vitamin D is also believed to play a role in serotonin activity, and lower levels may impact this important neurotransmitter.

In people who experience SAD during the summer months, it is often too much heat or too much light that triggers the onset of depressive symptoms.

HOW TO STOP FEELING SO SAD

If you experience SAD, there is hope. Many natural therapies can be helpful in reducing symptoms of depression, including the following.

1. Bright light therapy: A growing body of research shows that using bright light therapy, especially in the morning, is effective in treating SAD. Bright light therapy is full-spectrum light that has to be at least 10,000 lux or higher to be effective. “Full-spectrum” is important terminology. It means that the light is the same color spectrum as sunlight. Other types of light won’t do for the treatment of SAD. For this therapy, aim for 20-30 minutes of exposure in the morning.
2. Vitamin D supplementation: If you experience SAD, it’s critical to check your vitamin D levels and optimize them with a nutritional supplement if necessary.
3. Kill the ANTs: It’s common for people with SAD to fall into unhealthy negative thinking patterns. Learning to kill the ANTs (automatic negative thoughts) by challenging your thoughts can be helpful. Psychotherapy can be beneficial in showing you how to change your thinking habits.
4. Happy foods: Resisting the cravings to consume high-glycemic carbohydrates can help. As the winter months approach (and ideally year-round), focus your diet on foods that fight depression.

In some cases when natural treatments aren’t enough, medications may be helpful. It’s also important to look into other factors that may be contributing to depressive symptoms.