Seasonal affective disorder (SAD) is a type of depression that sets in or starts in the winter months. Unlike other types of depression, it is often a cyclical, recurring disorder — you'll feel depression every winter and begin to feel better each spring.
SAD depression is caused by lowered levels of serotonin, the mood-affecting brain chemical that is triggered by seasonal changes in daylight. Shorter days may also disrupt the body’s biological clock — circadian rhythm — which upsets the balance of melatonin, the hormone which regulates mood and sleep patterns.
SAD is far more common in northern climates, where days can be very short in winter. Replacing light bulbs in your home with full spectrum light bulbs can help because they emit light similar to sunlight.
Studies have shown that upping your exercise routine can counteract SAD. Exercise raises levels of serotonin and also increases levels of endorphins, which are responsible for runner’s high and have been shown to fight depression. Moderate exercise such as walking, riding a stationary bike, or swimming is a great way to get started.
Vitamin D is necessary for the synthesis of serotonin and dopamine (chemicals associated with depression), so researchers concluded that a link between low vitamin D levels and depression was logical. The Vitamin D Council recommends 2,000 IU daily, but suggests taking more if you get little exposure to the sun.
Another way to prevent SAD is to eat more fish. Fatty fish, such as salmon and sardines, contain omega-3 fatty acids. Studies have found that people who have low levels of two chemicals found in fish, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are at increased risk for depression.