Key Takeaways
For thousands of years, people have noticed that their moods change with the seasons.
But it wasn't until 1984 that researchers gave this pattern a name: Seasonal Affective Disorder.
This article traces the evolution of SAD from ancient observations to a recognized medical condition with proven treatments.
Ancient Observations of Seasonal Mood Changes
People have long noticed the connection between seasons and mood, long before modern medicine existed.
Hippocrates, the Greek physician from 460-370 BCE, was the first to document this link in medical terms.
He described melancholia as a distinct condition where "fears and despondencies, if they last a long time," characterized the illness.
Hippocrates built his theory on the four humors: blood, phlegm, yellow bile, and black bile. He believed an excess of black bile caused melancholia, and this imbalance worsened during autumn and winter.
The cold, dry conditions of fall supposedly promoted black bile production, triggering depressive symptoms.
Roman physicians also expanded on these observations.
Aretaeus of Cappadocia noted that some patients experienced seasonal patterns in their mood disorders.
He described people who became "dull or stern; dejected or unreasonably torpid, without any manifest cause" during specific times of year.
These ancient doctors lacked our modern understanding of brain chemistry and circadian rhythms.
They attributed seasonal mood changes to fluid imbalances rather than light exposure or neurological processes. But they got one thing right: seasons genuinely affected mental health in predictable patterns.
The Long Gap in Understanding

After the Greek and Roman physicians documented seasonal mood patterns, progress stalled for centuries.
During medieval Europe, depression became viewed primarily as a spiritual problem rather than a medical one.
A condition called acedia, meaning sloth or apathy, was identified by Christian scholars, typically linked to isolation and seen as a failure of will.
The theory of the four humors dominated medical thinking through the Renaissance.
Constantine the African, who died in 1087, wrote De Melancholia, which served as a bridge between ancient Greek medicine and Renaissance medical practice.
Physicians like Ambroise Paré continued using Galen's classifications well into the 1500s, still attributing prolonged sadness to corrupt humors.
However, the major shift came during the Islamic Golden Age and later the Enlightenment, when physicians began viewing melancholia through a more psychological and biological lens rather than purely spiritual.
But even then, the seasonal component remained poorly understood.
The term "depression" itself didn't emerge until the 1800s, derived from the Latin "depression" meaning a pressing down.
The Breakthrough Research of 1980-1984
The path to understanding SAD began with a seemingly unrelated discovery.
In 1980, Alfred Lewy and his team at the National Institute of Mental Health published a groundbreaking paper in Science showing that bright light suppresses melatonin production in humans.
This challenged the prevailing scientific belief that light didn't affect human circadian rhythms and that social cues were the main synchronizers of our internal clocks.
The breakthrough came when a patient approached Rosenthal's team with a unique observation. This patient had depression and noticed his symptoms followed seasonal changes.
He wondered if previous research on melatonin release at night could provide him with insight. Rosenthal and his colleagues treated the patient with bright lights, which successfully managed the depression.
Norman Rosenthal's personal experience made him receptive to this patient's observations.
When he emigrated from the mild climate of Johannesburg, South Africa, to the northeastern United States, he noticed dramatic changes in his own energy and productivity. As a resident in the psychiatry program at the New York State Psychiatric Institute, he felt more energetic during the long summer days compared to the shorter, darker winter days.
The 1984 paper, published in Archives of General Psychiatry, officially described SAD based on a study of 29 patients in Maryland.
Most patients had bipolar affective disorder, especially bipolar II.
Their depressions showed specific characteristics: hypersomnia, overeating, and carbohydrate craving. These symptoms appeared to be influenced by changes in climate and latitude.
Sleep recordings in nine depressed patients confirmed the presence of hypersomnia and showed increased sleep latency and reduced slow-wave (delta) sleep.
The term "Seasonal Affective Disorder" was deliberate, as the acronym SAD captured both the medical classification and the emotional reality of the condition.
Since the initial Maryland study, researchers have described the same condition in various parts of the world, including both the northern and southern hemispheres.
Studies have found that prevalence increases with distance from the equator. In Florida, SAD affected only 1.5% of the population, while in New Hampshire, it was almost 10%.
Understanding Why It Happens

The 1984 discovery opened the door, but researchers still needed to understand the biological mechanism behind SAD.
In the 1980s, Alfred Lewy proposed the dim light melatonin onset (DLMO) as a biomarker for circadian phase position.
This measurement became the most accurate way to assess when a person's internal clock was running relative to their sleep-wake schedule.
The leading explanation became the phase-shift hypothesis.
According to this theory, SAD results from circadian misalignment, specifically, the time interval between melatonin onset and the midpoint of sleep becomes disrupted.
Most SAD patients experience phase-delayed circadian misalignment, meaning their internal clocks run later than their actual sleep schedules.
When days get shorter, their circadian rhythms don't adjust properly to the reduced light exposure.
Research also identified a "sweet spot" for optimal circadian alignment, specifically a six-hour interval between the onset of melatonin and the midpoint of sleep.
Geography plays a significant role, as prevalence increases with distance from the equator.
Areas with more dramatic seasonal light changes tend to have higher rates of SAD.
Not everyone develops SAD despite living in the same latitude, however.
Research suggests that individual differences in the sensitivity of the circadian system to light influence whether someone develops the condition.
Some people's biological clocks respond more strongly to changes in light than others.
Evolution of Treatment and Diagnosis
In the 1980s, the term "seasonal affective disorder" was coined by Norman Rosenthal at the National Institute of Mental Health, and the DSM-III introduced major depression in the 1970s.
SAD became classified as a subtype of major depressive disorder with a seasonal pattern.
Light therapy evolved from those early experiments into a standardized treatment.
Scientists also discovered that low-dose melatonin taken in the afternoon or evening could provide a corrective phase advance for most SAD patients.
Organizations like the Seasonal Affective Disorder Association (SADA) were formed to support patients and advocate for recognition.
Light therapy for SAD gained endorsement from major medical institutions, including the National Institute for Mental Health, the Mayo Clinic, and the Cleveland Clinic.
The diagnosis requires recurrent depressive episodes with a seasonal pattern over at least two consecutive years, with seasonal episodes substantially outnumbering non-seasonal ones.
This specificity helps distinguish SAD from other forms of depression that might coincidentally worsen in winter.
From Mystery to Medicine
Seasonal Affective Disorder went from unexplained suffering to a recognized medical condition in just four decades.
If you're experiencing winter depression symptoms, you're not imagining it. The science proves it's real, and the treatments that emerged from this research history can help.
Want to learn more about managing seasonal depression? Check out our blog for practical guides on light therapy, lifestyle strategies, and expert insights on beating winter blues.