Seasonal Affective Disorder (SAD), often referred to as winter depression, occurs during the fall and winter months when daylight hours are shorter. Individuals with SAD experience emotional and physical symptoms that can interfere with daily life. Awareness of these symptoms and their causes supports timely management and helps maintain well-being during the winter months.
Even mild seasonal symptoms can affect daily functioning, with studies indicating that up to 30% of people experience noticeable drops in energy or mood during winter months, impacting work, social life, and motivation. Recognising these changes early can help individuals identify patterns and take steps to manage their well-being effectively.
Oversleeping and morning difficulty
Hypersomnia, or excessive sleep, is a common symptom of winter depression. Individuals may sleep for long periods and still feel fatigued upon waking. Mornings can feel especially difficult because reduced daylight affects brain chemistry and hormone levels. Matthew Snyder, LMFT, C-DBT, CAMS II, notes, “People who get too much sleep may feel drowsy and slow to start the day, which affects daily tasks and makes mood problems worse in the morning.”
He adds that oversleeping creates a paradoxical situation where the body gets more rest, but the mind feels less alert. “The quality of sleep matters as much as the quantity. Those suffering from winter depression are more likely to have disturbed sleep architecture, which means they will spend more time in bed without getting the restorative sleep they need.”
Changes in appetite and weight gain
Winter depression often brings changes in appetite. People may crave carbohydrate-rich foods such as bread, pasta, and sweets. This response is partly biological, as lower sunlight affects serotonin, a neurotransmitter linked to mood and appetite. Eating carbohydrates briefly increases serotonin, bringing a short sense of comfort but often leading to overeating and weight gain.
Reduced physical activity during colder months can intensify this pattern and further affect self-confidence and energy. The brain often turns to food as a quick way to restore balance when light and mood signals fall out of sync.
Low energy and fatigue
Persistent tiredness can occur even with enough sleep. Reduced sunlight lowers serotonin, which influences mood and energy, while increasing melatonin, the hormone that promotes sleep. Higher melatonin levels can leave individuals feeling mentally sluggish and less motivated. Konstantin Lukin, PhD, explains: “Since fatigue lowers both physical and mental energy, daily chores can seem too much to handle, and sticking to a routine can be hard.” He adds, “Feeling tired can also change your mood and make it harder to stay busy or connect with other people, which can make feeling tired and unmotivated even worse.”
Social withdrawal and mood changes
Some individuals withdraw from social activities and spend more time indoors during winter. This withdrawal can result from feelings of sadness or irritability. Mood swings, difficulty concentrating, and feelings of hopelessness can reinforce social isolation and intensify depressive symptoms. Recognizing these changes early can help individuals maintain connections and support emotional well-being.
Biological causes of winter depression
Changes in the circadian rhythm are closely linked to seasonal depressive symptoms. Shorter days reduce serotonin, a neurotransmitter that regulates mood, sleep, and appetite, while melatonin, the hormone that promotes sleep, increases. Vitamin D deficiency during periods of limited sunlight can further reduce serotonin levels and contribute to oversleeping, fatigue, low mood, and carbohydrate cravings.
Chronobiology evidence shows that people with SAD may experience longer nighttime melatonin secretion and altered serotonin function compared with those without seasonal depressive symptoms. Understanding these patterns clarifies why interventions that regulate sleep-wake cycles and increase morning light exposure, such as bright light therapy, can improve mood and energy.
Environmental and psychological factors
Shorter days and longer nights can affect mood and daily routines. Reduced sunlight limits outdoor activity, which can influence emotional state and increase feelings of isolation. Some individuals develop heightened negative thoughts about seasonal limitations, which can reinforce low mood. Kosta Condous, MA, LMFT, highlights: “Shorter lighting hours can be less of an issue if people change their daily routines and stay socially connected.”
He observes that structured daily routines and regular social engagement often prevent seasonal mood dips from becoming more serious. Addressing both lifestyle and biological factors supports mental health more effectively.
Identifying when to seek help
If symptoms persist or worsen, consulting a healthcare professional is important for proper evaluation and treatment. Early recognition of SAD can lead to more effective management. Screening tools and diagnostic criteria help determine severity, and professional guidance ensures the best approach.
One of the most well-supported treatments for winter depression is bright light therapy. Clinical studies, including a 2018 meta-analysis, show that morning exposure to high-intensity light can significantly reduce symptoms. Combining light therapy with structured routines and psychotherapy provides additional support.
Dr Konstantin Lukin is a licensed clinical psychologist and founder of the Lukin Center for Psychotherapy. He specialises in anxiety, depression, and emotional regulation, integrating cognitive behavioural and psychodynamic approaches. His work helps clients build resilience and insight by addressing how early experiences shape emotional health.
Kosta Condous is a licensed marriage and family therapist and co-founder of Higher Purpose Recovery. With extensive experience across inpatient and outpatient settings, he specialises in addiction, mental health, and co-occurring disorders. Kosta brings a leadership philosophy rooted in collaboration and creativity to elevate the standard of client care.
Matthew Snyder, LMFT, C-DBT, CAMS II, serves as clinical director at Journey Hillside Tarzana. He holds both a BA in psychology and an MA in clinical psychology, and is certified in dialectical behavior therapy and anger management. With deep experience treating trauma-related disorders and addiction, his approach emphasizes reducing shame, restoring hope, and developing skills for lasting recovery. Matthew is known for his authenticity, empathy and commitment to helping clients rebuild meaningful lives.