SAD has been treated by Light Therapy, Vitamin D, Melatonin, and Exercise

Getting Dark Early? How to Stay Happy - GreenMedInfo Dec 2021

Perplexity AI: Yes for Light Therapy, SSRI, CBT; Maybe for Vitamin D and Exercise

No. Light therapy, vitamin D, melatonin, exercise, and CBD do not have remotely equal evidence or status in treating SAD.

What guidelines say for SAD

Clinical guidelines and major reviews consistently list the following as primary, evidence‑based treatments for winter‑pattern SAD:
- First‑line / well‑supported:
- Bright light therapy (10,000 lux in the morning).[1][2] - Antidepressants (especially SSRIs).[3][1] - Cognitive‑behavioral therapy tailored to SAD.[4][1] - Adjunct / possible role:
- Vitamin D (mainly when deficient).[5][6][7] - Exercise and outdoor activity.[8][9][10][11]

CBD is not mentioned in mainstream SAD guidelines at all.[7][1]

Light therapy

  • Light boxes at 2,500–10,000 lux for 30–60 minutes each morning are recommended first‑line by primary‑care and psychiatric guidelines for SAD.[2][1][7]
  • Multiple controlled trials and meta‑analyses show that bright light can be comparable in effect size to antidepressants for winter depression, with onset in days to weeks and generally mild side effects.[6][3][2]

So among your list, light therapy has the strongest and most specific evidence for SAD.

Vitamin D

  • A small pilot trial reported vitamin D supplementation produced greater improvement in SAD symptoms than light therapy, but this has not been reliably replicated and overall evidence remains limited and inconsistent.[5][6]
  • Large reviews note no consistent difference in baseline vitamin D levels between SAD patients and controls, and light therapy’s effect appears independent of vitamin D status.[6]

Vitamin D is recognized as a possible treatment or adjunct (especially in deficiency) but is not considered equivalent to light therapy as a core, proven SAD treatment.[7][5][6]

Melatonin (not "first line")

  • Melatonin and circadian phase–shifting strategies are discussed as options because SAD is closely tied to circadian misalignment, but they are not first‑line in general clinical guidelines.[5][6][7]
  • Evidence is mixed: correct timing and low doses may help in some patients, but the therapeutic window is narrow and data are weaker than for bright light or antidepressants.[6]

So melatonin can be useful in selected cases but is not on par with light therapy as a mainstay treatment.

Exercise (not as good as SAD lights)

  • Randomized trials in winter show both aerobic exercise and bright light can improve depressive symptoms, with bright light often outperforming exercise on atypical symptoms.[9]
  • Exercise plus bright light appears particularly beneficial, and reviews conclude that physical activity can help SAD symptoms but is usually framed as an adjunct lifestyle intervention rather than a stand‑alone primary treatment.[10][11][8]

Thus exercise is helpful and recommended as part of management but is not considered equivalent to light therapy in evidence or guideline status.

CBD (No RCT yet)

  • There are no randomized controlled trials specifically testing CBD for SAD. Available data are:
    • General depression/anxiety studies suggesting possible antidepressant/anxiolytic effects, often small or preliminary.[12][13][14]
    • Opinion and marketing pieces extrapolating from ECS–mood links or general depression data to SAD.[15][16][17][18]
  • CBD does not appear in NIMH or primary‑care guidelines for SAD treatment.[1][7]

CBD is therefore experimental/off‑label and definitely not equivalent to light therapy or other established SAD treatments.

Bottom line for your list

  • Clearly evidence‑based and guideline‑supported for SAD:

    • Light therapy (primary).[2][1][7]

  • Adjuncts / possibly helpful, evidence weaker or more conditional:

    • Vitamin D (especially if deficient).[7][5][6]
    • Exercise (beneficial, best combined with light/other treatments).[11][8][9][10]
    • Melatonin (circadian‑targeted, with mixed and protocol‑sensitive evidence).[5][6]

  • Experimental / not established for SAD:

    • CBD (no SAD‑specific RCTs; only general depression/anxiety signals).[13][14][15][12]

So they are not equally effective or equally recommended; light therapy sits at the center, with the others ranging from useful adjuncts (vitamin D, exercise, possibly melatonin) to unproven (CBD) for SAD.

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Related in Google Scholar

  • Effectiveness of visible light for seasonal affective disorder: A systematic review and network meta-analysis - White light best, July 2025 FREE PDF DOI: 0.1097/MD.0000000000043107
  • Seasonal Affective Disorder: A Narrative Review doi.org/10.61440/JCPN.2024.v2.14 FREE PDF
  • Effect of Light Therapy on Reducing Depressive Symptoms in Seasonal Affective Disorder Sufferers - April 2024 FREE PDF
  • Treatment measures for seasonal affective disorder: A network meta-analysis April 2024 FREE PDF light sort of helps
  • 100,000 lumens to treat seasonal affective disorder: A proof of concept RCT of Bright, whole-ROom, All-Day (BROAD) light therapy - whole room is about as good as a light box - Aug 2022 FREE PDF

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