Seasonal affective disorder (SAD), also known as winter depression, is a type of depression linked to change in the seasons. The strange depression is thought to be caused by a lack of light. Some decades ago, SAD was not a problem. Then how it was recognized as a disorder?

More than three decades ago, a story by Washington Post had a beginning: 'I should have been a bear'. The subject in the story was a women suffering from depression in the fall. Norman Rosenthal, a researcher from the National Institutes of Mental Health, studied light's impact on mental health. The researcher concluded that in diminishing exposure to sun, brain of an individual responds negatively.

The reporter of that article asked people who too experienced depression due to change in weather to contact Rosenthal. In an interview, he said, "I thought I was dealing with a very rare syndrome. I thought we'd get maybe half a dozen and we could do something. We got 3,000 responses from all over the country".

In 1984, Rosenthal identified the problem due to weather change and labeled it 'Seasonal Affective Disorder (SAD)'. The researcher spent about 30 years of his career to study the problem and find cure for it.

In 1987, SAD was included in American Psychiatric Association's official manual as a depression problem. Today, more than 10 million individuals in the US are thought to be struggling with depression induced by lack of light.

According to the U.S. National Library of Medicine, SAD happens during the winter months where people experience various symptoms of depression including “sad, anxious or ‘empty’ feelings” because of the lack of sunlight.

One reason why some may be affected is because a lot of hormones can be regulated by sunlight, including once called serotonin, which health experts say goes down when the days get shorter.

Experts also say SAD can be remedied with “light or photo therapy,” where for sessions of 10 to 30 minutes, patients sit and look at a light box.

Eating healthy during the winter months is another way to keep energy up. While challenging during the holidays, limit carbohydrates, which provide only a quick jolt of good feelings. They wear off, blood sugar drops and lethargy kicks in. Rosenthal says SAD suffers should be mindful of eating more protein-rich and nutrient-dense foods like lean meats and vegetables and less sugary, processed items like candy or white flour-based products.

Rosenthal recently updated his book to include this treatment for SAD. By bringing your mind to the present, people often feel calmer, less anxious and can concentrate more. People find these practices help them regulate their emotions.