The strongest evidence of human seasonality comes in the form of winter depression, or Seasonal Affective Disorder (SAD). Individuals with SAD usually suffer from depressive episodes beginning in late autumn or early winter, and start to feel better when spring or summer approaches. Living in a northern locale with harsh winters and extended darkness can affect your levels of melatonin, a hormone that impacts sleep. When daylight hours decrease, melatonin levels increase, which can cause fatigue and depression for some.
Extended darkness also disrupts the body’s circadian rhythm because decreased exposure to sunlight tells the body to be asleep when it should be waking up. Light provides you with environmental cues that influence pupil dilation, alertness, heart rate and melatonin levels. In fact, the light that enters the retina of the eye actually sets your circadian rhythm.
This response to the seasons can happen in reverse when the weather turns warm and sunny, and your body starts receiving extended exposure to light. Some individuals experience insomnia, or become more anxious, irritable and hyperactive during the spring and summer. This condition is called Reverse Seasonal Affective Disorder.
Each person's circadian rhythm is different, depending on their genetics and environmental circumstances. Plus, with increased urbanisation, people tend to spend more time working indoors in windowless offices than they did in past eras. The resultant lack of sunlight can cause a decrease in the body's levels of vitamin D, serotonin and dopamine, which can affect brain chemistry.
Light therapy, or photo therapy, has been found to be extremely helpful for alleviating some depressive symptoms. Light treatment uses artificial lights to imitate light from the outdoors, thereby triggering changes in the brain that can help elevate serotonin and dopamine levels. You can also use dawn simulators that mimic sunrise to help you wake up without feeling groggy. Thirty minutes of daily exercise can also help balance your brain chemistry and increase your energy levels. In milder cases of SAD, the addition of extra omega-3 fatty acids to an already balanced diet has been shown to relieve some depressive symptoms.
If you notice that you experience a seasonal pattern of winter depression and feel that your symptoms are severe, seek help from a professional. Try to keep a diary of behavioural changes so that you can provide accurate information about your symptoms to your doctor. Practice a healthy lifestyle every day so that you can enjoy every season of the year.