Is It Seasonal Affective Disorder or Your Hormones?

The “winter blues” are real. Seasonal Affective Disorder (SAD) affects roughly 5% of U.S. adults, and nearly 4 in 10 people say their mood reliably tanks in winter.^{1 2} Less sunlight, shorter days, and melatonin going into overdrive all play a role.

While SAD can be a convenient scapegoat for every low mood between November and March, its symptoms—like fatigue, irritability, low motivation—can also be driven by hormone imbalances.

“Hormonal changes affect serotonin, dopamine, sleep, metabolism—essentially all the systems people assume are disrupted by winter,” says Natalie Kunsman, M.D., an integrated health advisor and physician specializing in family medicine, regenerative medicine, and hormonal health in Colorado Springs, CO. “So anytime someone struggles with low mood, hormones should always be part of the diagnostic conversation.”

SAD 101: Why Winter Hits Like a Ton of Wet Snow

SAD is a subtype of depression with a fairly predictable pattern. Symptoms typically emerge in late fall, peak in winter, and improve as daylight returns. The usual drivers include shorter days disrupting circadian rhythm, seasonal drops in serotonin activity (less light hitting the retina alters brain chemistry), and increased melatonin production (darkness extends the time your body spends producing it).^{3 4}

These shifts explain classic SAD symptoms: low energy, heavier sleep, carb cravings, social withdrawal, and a strong desire to hibernate. But hormones regulate many of these same functions, which is why it can be difficult to pinpoint the source of your symptoms.

How Hormones Shape Mood

Hormones help regulate energy, motivation, stress tolerance, and emotional resilience.

Adding to the confusion, hormones themselves may follow a seasonal rhythm. Population studies show that testosterone levels tend to dip in winter months ^{6 7}. Cortisol rhythms also vary by season, with measurable changes in stress-hormone dynamics across the year ^{8 9}. In other words, winter doesn’t necessarily cause hormone imbalance—but it can amplify existing vulnerabilities.

Thyroid hormones and mood

Thyroid hormones play a critical role in mood regulation. Low thyroid function (hypothyroidism) is associated with fatigue, low mood, brain fog, and slowed thinking—symptoms that can closely resemble depression or SAD. Thyroid function can also subtly decline with age or stress, causing mild mood changes. ¹⁰

Men’s hormone health and mood

Low testosterone has a well-documented relationship with anxiety, irritability, depressed mood, and low motivation. Men with clinically low testosterone (hypogonadism)—and even those at the lower end of the normal range—report higher depressive and anxiety symptoms than men with optimal levels ^{11 12}.

Because testosterone declines naturally with age, many men develop these symptoms gradually and may not recognize the hormonal shift until they’re well into it. Roughly 1 in 10 middle-aged and older men have testosterone levels low enough to be clinically concerning, and several million U.S. men experience symptomatic low testosterone that can affect mood, energy, libido, and overall well-being. The proportion increases sharply with age—for example, up to ~40% of men over 45 may have testosterone levels below optimal ranges.¹³

Winter often intensifies the problem, leading many men to assume they’re dealing with seasonal depression.

Randomized, placebo-controlled trials show that testosterone replacement therapy significantly reduces depressive symptoms in men with low testosterone, reinforcing the biological role hormones play in male mood health.¹⁴

Women’s hormone health and mood

Women’s hormones fluctuate monthly and across life stages, and those shifts can feel a lot like SAD.

• Monthly Cycles: Menstrual cycles cause natural hormone shifts across the month that can impact mood. When these shifts coincide with winter-related sleep disruption and reduced daylight, emotional symptoms may feel more intense, blurring the line between hormonal and seasonal mood changes.
• Perimenopause: During perimenopause, which affects some two million women each year,¹⁵ estrogen, progesterone, and testosterone fluctuate unpredictably rather than declining in a straight line. Research consistently shows that hormonal fluctuations across the menstrual cycle and perimenopause significantly affect mood and emotional regulation.¹⁶ Women who are hormonally sensitive may experience stronger mood disruptions during winter, when circadian rhythm and sleep are already strained. ¹⁷
• Menopause: Some 1.3 million American women enter menopause each year.¹⁷ As estrogen levels decline and stay low, the brain loses one of its key mood stabilizers, often leading to persistent low mood, irritability, anxiety, fatigue, and brain fog. Clinical research shows that lifting levels of estrogen and progesterone with hormone replacement therapy (HRT) can reduce emotional symptoms, including anxiety—underscoring how tightly estrogen levels are linked to mood regulation.¹⁸

SAD vs. Hormone-Driven Mood Changes: How to Tell the Difference

One of the biggest clues is pattern. SAD follows the calendar. Hormone-driven mood issues stick around past winter.

Some patterns that may suggest that your symptoms aren’t strictly seasonal:

The only definitive way to determine the underlying cause of low mood is through blood testing. Your doctor will consider both your test results and the signs and symptoms you describe to reach the right diagnosis.

“I’ve found many patients have come in at the behest of their psychologist, therapist, or psychiatrist, recognizing that some of these overlapping symptoms may have hormonal issues contributing or causing them,” Kunsman says.

How Hormone-Driven Mood Issues Are Treated

If testing shows that your mood changes are driven by hormones, treating the underlying driver—whether that’s low testosterone, perimenopause, menopause, or thyroid dysfunction—can help resolve them.

Testosterone Replacement Therapy (TRT)

Lifestyle changes and supplements may help support testosterone, but some men need medical treatment to restore levels to a healthy range. A large meta-analysis found that testosterone therapy was associated with meaningful improvements in depressive symptoms in men with low testosterone.²⁰

Testosterone is not an antidepressant—but for men whose mood symptoms are tied to low testosterone, treating the deficiency can make a real difference. If you’re considering TRT, work with a healthcare provider who can monitor your levels and discuss possible side effects.

Menopause Hormone Therapy

Though hormone replacement therapy (HRT) is primarily used to address the physical symptoms around menopause, like hot flashes, night sweats and vaginal dryness, it can also play a role in managing emotional symptoms, including anxiety. ^{21 22}

In a well-designed clinical trial, women who used transdermal estradiol with intermittent micronized progesterone were about half as likely to develop clinically significant depressive symptoms compared with those on placebo. ²³

Depending on your individual needs, hormone therapy may include estrogen or estradiol, progesterone, and low-dose testosterone. ^{24 25 26} Hormone therapy is not a universal fix, and outcomes vary based on timing, formulation, and individual biology. Many women benefit most from a combined approach that includes lifestyle support, therapy, and—when appropriate—antidepressants.

Thyroid Medication

When thyroid hormones are out of range, treating the thyroid disorder itself will help lift mood. Restoring thyroid hormone levels can also improve energy, cognitive function, and depressive symptoms—sometimes eliminating the need for additional psychiatric treatment. ²⁷

About the author

Aviva, Hone’s Executive Editor, is an award-winning health-science journalist and former executive editor of Psychology Today, Reader’s Digest, and The Healthy. She has written for national print and digital publications including Health, Prevention, Women’s Health, Men’s Health, Shape, Fitness, SELF, New York Magazine, and more.

About the reviewer

Natalie Kunsman, M.D., is a board certified physician specializing in functional, anti-aging, and regenerative medicine. She is a fellow of the American Academy of Anti-Aging medicine and the American Academy of Family Physicians.