Seasonality or Seasonal affective disorder (SAD) is seasonal changes in mood and behavior associated with day light. Symptoms start in the fall and continue into the winter months, sapping a person’s energy and making them feel moody. Less often, SAD causes depression in the spring or early summer. SAD begins and ends at about the same times every year. A study of over 4,000 individuals identified several genetic variants with small additive effects that are significantly associated with SAD. People with these genetic variant who feel moody in winter may consider adding exercise and getting good amounts of natural light to combat the low energy state.

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