As winter approaches, you may feel more down and out than usual. This could be due to a condition known as seasonal affective disorder (SAD). SAD is a type of depression. It occurs at the same time each year, often during the fall and winter seasons when there’s less natural sunlight.

Seasonal affective disorder impacts up to 3% of the general population. And as Johns Hopkins Medicine reports, it can increase with age.

According to Johns Hopkins, while research hasn’t identified a direct cause of the disorder, it may be linked to vitamin D deficiency, a condition that puts older adults at risk for health issues such as diabetes, cancer, heart disease, and overall poor health. Additionally, SAD symptoms such as trouble sleeping, memory and concentration difficulties, and weight gain can correspond to physical and lifestyle changes associated with aging.

While scientists don’t fully understand the causes of SAD, recognizing its symptoms can help you take preventative action or seek treatment.

What Causes SAD?

It’s not clear what causes seasonal affective disorder, but research shows that many people with the condition also have vitamin D deficiency, reduced serotonin activity, and/or excessive melatonin production. This can make it difficult to adapt to changing daylight hours throughout the seasons. SAD isn’t limited to the winter months, either: It’s less common, but some people experience the condition in the spring and summer.

Daylight savings time can also affect how you feel during the winter. When daylight savings time ends, less sunlight means less opportunity for the body to produce vitamin D and encourage serotonin activity. This can exacerbate symptoms of seasonal affective disorder, especially in northern parts of the world with less winter daylight.

What’s the Difference Between SAD and Depression?

Both SAD and depression can cause similar symptoms, but they aren’t exactly the same.

SAD occurs in response to a change in seasons. Symptoms can also vary depending on the severity of the season; people in milder climates may be less likely to experience severe SAD.

Depression, meanwhile, isn’t tied to the seasons. It’s linked to various factors including genetic predisposition and life stressors.

Symptoms of depression can include feelings of sadness, loss of interest in activities, and difficulty sleeping, regardless of the season.

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