Seasonal affective disorder hormones: How to tell SAD from low testosterone in men

SAD usually follows a repeatable fall-to-winter pattern and improves in spring, while low testosterone is more likely when symptoms are persistent, come with libido or erection changes, and are confirmed on repeat morning blood tests. If your symptoms do not cleanly follow the calendar, or they come with sexual or sleep changes, it is time to look at seasonal affective disorder hormones together and not as separate problems.

Key takeaways

• If symptoms persist past spring, or begin in your 30s to 50s, consider a hormone and thyroid workup in addition to screening for seasonal affective disorder.
• Meta analyses suggest symptomatic men with total testosterone below 350 ng/dL or free testosterone below 100 pg/mL are the most likely to feel mood improvement when testosterone is restored.^[4],[5]
• In men with suspected secondary hypogonadism who want to preserve fertility, a clinician may consider a SERM (such as clomiphene or enclomiphene where available) after repeat morning testosterone testing and LH/FSH evaluation.
• A practical first step is a 14 day log of sleep timing, morning energy, libido, and mood, plus morning fasting labs that include total and free testosterone and thyroid markers.
• Bright light therapy has evidence for seasonal depression, but a poor response should prompt a broader sleep and hormone evaluation.^[6]

Why winter mood and male hormones get confused

Seasonal affective disorder, also called SAD, is a subtype of depression with a predictable seasonal pattern. Symptoms usually show up in late fall, peak in winter, and ease when daylight returns.^[1] The twist is that male hormone problems can produce a similar symptom cluster, including fatigue, irritability, low motivation, heavier sleep, and social withdrawal. That is why “seasonal affective disorder hormones” is a useful framing for men. It forces a broader clinical differential diagnosis, not a guess.

According to a major clinical overview in Chronobiology International, SAD is tightly linked to changes in light exposure and biological timing systems, not just “feeling down when it is cold.”^[1] Those same timing systems also influence hormones, especially cortisol and testosterone rhythms. When winter nudges your sleep schedule later, reduces morning light, and shifts stress patterns, it can amplify any borderline hormonal vulnerability you already have.

Research published in The Journal of Clinical Endocrinology and Metabolism and related databases shows measurable seasonal variation in serum testosterone, with lower levels often seen in winter months. That does not mean winter “causes” hypogonadism, which is clinically low testosterone. It means winter can make a modest hormone dip feel bigger, especially if you are already near the low end of your personal range.

How seasonal affective disorder hormones interact

Light, circadian rhythm, and melatonin

Circadian rhythm is your internal 24 hour clock that times sleep, wake, temperature, and hormone release. Shorter winter days can disrupt circadian rhythm, partly because less light hits the retina, which is the light sensing tissue at the back of the eye. In SAD, this timing shift is linked to depressive symptoms and to changes in melatonin, a hormone that signals “biological night.”^[1]

Melatonin is a sleep timing hormone released in darkness. Longer dark periods can extend melatonin production, which may contribute to heavy sleep and low daytime energy in people prone to SAD.^[1] In men, that can also interact with testosterone because sleep quality and timing influence morning testosterone peaks.

Serotonin and dopamine are mood chemistry that hormones can influence

Serotonin is a neurotransmitter that supports mood stability and emotional resilience. Dopamine is a neurotransmitter tied to motivation, drive, and reward. In SAD, reduced daylight is associated with seasonal shifts in serotonin activity, which can lower mood and increase “hibernation” behaviors like cravings and withdrawal.^[1]

Testosterone can influence mood by interacting with neurotransmitter systems related to serotonin and dopamine signaling, which is one reason low testosterone can look like depression in men.^[4] The practical point is not that testosterone is an antidepressant. The point is that if a man’s winter depression is actually a testosterone problem, treating the hormone deficit can remove a major biological drag on mood.

Winter can nudge testosterone and cortisol rhythms

According to a 2023 study drawing on large institutional databases, serum testosterone shows seasonal variation, with winter months commonly associated with lower measurements compared with other seasons. A prospective clinical trial also found seasonal variation in male hormone levels alongside behavior changes. These are population level signals. For an individual man, the key is whether the seasonal dip drops you below a symptomatic threshold.

Cortisol is the main stress hormone that helps regulate alertness, blood sugar, and stress tolerance. A 2025 systematic review of hair cortisol, which reflects longer term cortisol exposure, found measurable seasonal variation across studies. Sleep timing and circadian misalignment can also change cortisol dynamics, which is relevant because winter sleep often becomes later and longer.

Clinical threshold to know: Meta analyses indicate that symptomatic men with total testosterone below 350 ng/dL, which is about 12 nmol/L, or free testosterone below 100 pg/mL, which is about 10 ng/dL, are most likely to benefit from testosterone restoring treatment when symptoms persist.^[4],[5] In practice, many clinicians use 350 ng/dL total or 100 pg/mL free as decision thresholds when the symptom story fits.

Thyroid hormones set the pace for energy and mood

Thyroid hormones help regulate metabolism, temperature, and brain function. Hypothyroidism is low thyroid function that can cause fatigue, low mood, brain fog, and slowed thinking. Those symptoms can look like depression and can easily be mislabeled as SAD if they worsen in winter when you are already sluggish.^[2]

According to a 2011 review in Journal of Thyroid Research, thyroid dysfunction is linked with depressive symptoms, and treating hypothyroidism can improve mood, cognition, and energy in many patients.^[2] A modern clinical review of hypothyroidism also emphasizes that low thyroid can present with non specific symptoms that overlap with psychiatric complaints.^[3]

Conditions that can look like SAD in men

When men search “seasonal affective disorder hormones,” they are often trying to answer a simple question: Is winter doing this to me, or is my body changing? These are the most common clinical look alikes in men that deserve a real workup.

Clinicians usually start by confirming the pattern: a consistent fall or winter onset with spring remission, typically repeating for at least two seasons, and symptoms that are not better explained by another medical or psychiatric condition.^[1] They also take a full mood history (including screening for bipolar disorder), review medications and alcohol use, and assess sleep timing and sleep quality.

When the story is not clearly seasonal, or when sexual symptoms, major sleep disruption, or unexplained weight or temperature changes are present, testing helps separate look alikes. Common next steps include repeat morning total testosterone (often with free testosterone) plus LH/FSH to evaluate for secondary hypogonadism, TSH and free T4 for thyroid disease, and targeted sleep evaluation (and, when indicated, home sleep apnea testing or polysomnography). Findings such as consistently low morning testosterone on repeat testing, elevated TSH with low free T4, or marked obstructive sleep apnea point away from SAD as the primary driver.

• Seasonal affective disorder: A seasonal pattern of depressive symptoms tied to changes in daylight and circadian timing.^[1]
• Male hypogonadism: Clinically low testosterone with symptoms such as depressed mood, irritability, low motivation, and low libido. Meta analyses show testosterone treatment can reduce depressive symptoms in men with low levels.^[4],[5]
• Thyroid dysfunction: Hypothyroidism can mimic depression and fatigue syndromes and may improve when thyroid hormone levels are corrected.^[2],[3]
• Chronic stress with altered cortisol dynamics: Seasonal and sleep related changes in cortisol rhythm can affect energy, mood stability, and stress tolerance.
• Sleep and circadian disorders: Delayed sleep timing, insomnia, obstructive sleep apnea, and irregular schedules can worsen winter mood and reduce daytime energy and motivation.

Limitations note: Seasonal shifts in testosterone or cortisol do not prove causation for depression. They show patterns at the group level. You still need symptom correlation and diagnostic testing to decide what is clinically meaningful for you.

Symptoms and signals to watch for

SAD and hormone driven mood changes overlap, so your goal is not to self diagnose. Your goal is to spot clues that your winter depression might involve seasonal affective disorder hormones, not just “winter blues.”

Focus on differentiators: SAD tends to be strongly seasonal (late fall onset, spring relief) and often comes with hypersomnia and low daytime energy, while low testosterone is more suspicious when symptoms persist outside winter and are paired with reduced libido, fewer morning erections, or new erectile changes. Insomnia or early morning awakening can occur in many depressive states, but if you are not improving by spring, it argues against a purely seasonal pattern. Seek urgent evaluation if you have suicidal thoughts, feel unsafe, or your symptoms cause severe functional impairment (for example, missing work, stopping eating, or being unable to care for yourself).

• Calendar pattern: SAD usually ramps up in late fall, peaks in winter, and improves with longer daylight.^[1]
• Symptoms that do not fully lift in spring: This is a common red flag for non seasonal drivers such as low testosterone or thyroid dysfunction.
• Low libido or sexual functioning changes: Reduced desire, fewer morning erections, or a new drop in sexual performance alongside low mood can point toward testosterone involvement.
• Heavier sleep but worse energy: Sleeping longer yet feeling unrefreshed can occur in SAD, but it is also common in hypothyroidism and dysregulated cortisol patterns.^[2]
• Increased irritability and lower stress tolerance: This can be a depression symptom, a cortisol rhythm issue, or part of androgen deficiency in men.^,[4]
• Age and timing: If symptoms begin in your 30s, 40s, or 50s, do not assume it is “just winter.” Testosterone tends to decline with age, and thyroid function can shift with stress and aging.^[3]
• Little response to light therapy or vitamin D: If you try standard seasonal strategies and feel no meaningful change, it strengthens the case for a hormone and sleep evaluation.

What to do about it

You do not need to choose between “it is SAD” and “it is hormones.” In men, the most effective plan is often to evaluate both tracks in parallel, then treat the dominant driver.

1. Step 1: Confirm the pattern and get the right labs Start with a 14 day log: sleep and wake times, morning energy, mood, cravings, training performance, and libido. Then schedule morning fasting blood work. At minimum, ask for total testosterone and free testosterone, plus thyroid testing. Thyroid testing typically includes TSH, which is thyroid stimulating hormone that tells the thyroid how hard to work, and free T4, a main circulating thyroid hormone.^[2],[3] If you are exploring fertility preserving options or possible secondary hypogonadism, include LH and FSH, the pituitary signals that help regulate testicular hormone production.
2. Step 2: Match treatment to the diagnosis, not the season According to a 2005 meta analysis in American Journal of Psychiatry, bright light therapy is an evidence based treatment for seasonal depression, especially when symptoms follow a classic winter pattern.^[6] If labs point to testosterone deficiency, treatment can include sleep and lifestyle support and, when appropriate, medication. Meta analyses show testosterone therapy is associated with reduced depressive symptoms in men with low testosterone.^[4],[5] For men with secondary hypogonadism who wish to preserve fertility, a clinician may consider a SERM (such as clomiphene or enclomiphene where available) to stimulate endogenous testosterone production after repeat morning testosterone testing and LH/FSH evaluation. If thyroid hormones are out of range, treating hypothyroidism can improve mood, energy, and cognition.^[2],[3]
3. Step 3: Monitor and adjust like a protocol, not a one time fix Whether you are using light therapy, psychotherapy, antidepressants, a SERM, testosterone cypionate, or thyroid medication, follow up testing matters. Hormones change with sleep, weight, stress, and season. Plan repeat labs and symptom review, then adjust dose and timing based on objective results and how you actually feel.

If you want an organized way to do this, a clinician can help you build a structured plan: confirm whether your symptoms meet criteria for a seasonal pattern, review sleep and lifestyle factors, order targeted morning labs (typically including testosterone and thyroid testing), and then monitor symptom changes alongside repeat testing. This approach is especially helpful when the question is not just “SAD or not,” but how sleep timing, thyroid status, testosterone, and stress physiology may be interacting in your case.

Myth vs fact

• Myth: “If I feel depressed in winter, it is definitely seasonal affective disorder.”
  Fact: SAD is defined by a seasonal pattern, but low testosterone, thyroid dysfunction, and altered cortisol rhythms can mimic the same symptoms in men.^[1],[2]
• Myth: “Light therapy not working means I am just ‘treatment resistant.’”
  Fact: A poor response should prompt a broader evaluation, including testosterone and thyroid testing, because the driver may not be light mediated.^[6]
• Myth: “Testosterone therapy is an antidepressant.”
  Fact: Testosterone is not an antidepressant, but meta analyses show mood benefits in men whose depressive symptoms are linked to low testosterone.^[4],[5]
• Myth: “If my testosterone is ‘normal,’ hormones cannot be involved.”
  Fact: Symptoms, free testosterone, seasonal variation, sleep, and thyroid status all matter. Some men feel significantly worse when levels fall to the low end of their personal range, especially in winter.
• Myth: “All testosterone treatment shuts down fertility.”
  Fact: Exogenous testosterone can suppress sperm production, but in some men with secondary hypogonadism who want to preserve fertility, clinicians may use medications such as SERMs (for example, clomiphene or enclomiphene where available) to support endogenous testosterone production.

Bottom line

In men, winter depression is not always just seasonal affective disorder. SAD is suggested by repeatable fall or winter onset, spring remission, and meaningful improvement with bright light therapy, while hypogonadism is suggested by symptoms that are year round or persist into spring plus libido or erection changes and is confirmed with repeat morning testosterone testing (often with LH/FSH to clarify the cause). If your pattern is unclear, symptoms are severe, or you notice sexual or major sleep changes, see a clinician for evaluation and a plan that may include light therapy, sleep treatment, psychotherapy, and hormone or thyroid management.

References

1. Magnusson A, Boivin D. Seasonal affective disorder: an overview. Chronobiology international. 2003;20:189-207. PMID: 12723880
2. Hage MP, Azar ST. The Link between Thyroid Function and Depression. Journal of thyroid research. 2012;2012:590648. PMID: 22220285
3. Taylor PN, Medici MM, Hubalewska-Dydejczyk A, et al. Hypothyroidism. Lancet (London, England). 2024;404:1347-1364. PMID: 39368843
4. Zarrouf FA, Artz S, Griffith J, et al. Testosterone and depression: systematic review and meta-analysis. Journal of psychiatric practice. 2009;15:289-305. PMID: 19625884
5. Walther A, Breidenstein J, Miller R. Association of Testosterone Treatment With Alleviation of Depressive Symptoms in Men: A Systematic Review and Meta-analysis. JAMA psychiatry. 2019;76:31-40. PMID: 30427999
6. Golden RN, Gaynes BN, Ekstrom RD, et al. The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. The American journal of psychiatry. 2005;162:656-62. PMID: 15800134