Fish oil

EPA & DHA (long-chain omega-3s) affect brain biology — they change neuronal membrane fluidity, neurotransmitter function (serotonin, dopamine), and reduce neuro-inflammation — processes thought relevant to depression and therefore to SAD. MDPI

Epidemiology supports a link — populations with high fish intake generally show lower rates of depressive illnesses; dietary shifts away from fish have correlated with rising mood disorder rates in some communities. That association is hypothesis-generating (not proof). ScienceDirect

Inflammation link — SAD and some depressive states show inflammatory markers; omega-3s have anti-inflammatory actions which may contribute to symptom improvement in some patients. MDPI

• Prefer EPA-predominant formulas (or an EPA:DHA ratio >2:1). Meta-analyses and clinical practice guidelines found EPA-dominant preparations more likely to show benefit than DHA-dominant ones. Psychiatrist.com
• Typical therapeutic net EPA dose: ~1,000–2,000 mg (1–2 g) EPA per day (net EPA) — either as pure EPA or as a combination with DHA where EPA is the dominant component. This dosing is what the International Society for Nutritional Psychiatry Research (ISNPR) practice guideline recommends for major depressive disorder and is commonly used in trials. BioMed Central
• Duration: most randomized trials test omega-3s for at least 8–12 weeks before expecting measurable clinical benefit. Plan for a trial of at least 2–3 months. ScienceDirect
• Use as adjunct, not automatic replacement — the ISNPR guideline recommends omega-3s as an adjunct option (especially for MDD). For SAD, do not stop proven treatments (light therapy, CBT, antidepressants) to try fish oil without medical oversight. Karger
• Product quality: choose products with third-party testing seals (USP, NSF, ConsumerLab) or prescription omega-3s where available — this reduces risk of contamination and ensures labeled EPA/DHA content. Verywell Mind

How to implement (example regimen clinicians commonly use):

• Pick an EPA-dominant product that delivers ~1,000 mg EPA per day (or 1–2 g EPA/day).
• Take with food (reduces GI side effects and “fishy burps”).
• Reassess depressive/SAD symptoms after 8–12 weeks; if partial response, discuss continuing (or adjusting dose) with your clinician. BioMed Central

Important note: there are relatively few high-quality RCTs done only in SAD; most evidence comes from trials/meta-analyses in MDD and general depressive symptoms. Below are influential systematic reviews, meta-analyses, and guidelines that support (or clarify limits of) omega-3 use for depression — which is the basis clinicians use when considering SAD.

Key systematic reviews / meta-analyses / guidelines:

• ISNPR Practice Guidelines (2019) — consensus practice guideline recommending 1–2 g net EPA/day (EPA-predominant or EPA:DHA >2:1) as an adjunct for major depressive disorder. This guideline is widely referenced for clinical dosing and formulation guidance. Karger
• Meta-analyses showing efficacy (with nuance): several recent meta-analyses conclude some antidepressant benefit — especially for EPA-predominant formulas — but trials are heterogeneous. Examples: Translational Psychiatry meta-analysis (2019) and other pooled analyses that identify EPA proportion and trial design as key modifiers of effectiveness. Nature
• BMC Psychiatry / network meta-analysis — found higher doses/EPA-predominant formulations more likely to show benefit in MDD; recommended considering EPA 1–2 g/day in practice. BioMed Central
• Cochrane review (2015, updated commentary) — concluded evidence was mixed/insufficient at that time to strongly recommend omega-3s for MDD; subsequent higher-quality trials and consensus guidelines have narrowed the recommendations toward EPA-predominant adjunctive use. (This explains why the field is still evolving.) Cochrane

Clinical trials (examples / representative trials):

• Several randomized, placebo-controlled trials (various sizes) have tested EPA-rich or EPA/DHA combos and reported reductions in depressive symptoms vs placebo — findings vary by dose, EPA fraction, and patient population. A selection of representative trials and RCTs are cited and summarized in the above meta-analyses and ISNPR guideline. (See the meta-analyses/guideline links above for trial lists and PDFs.) Nature

Summary on evidence: the best current synthesis supports some antidepressant benefit from EPA-predominant fish-oil (1–2 g EPA/day) as an adjunct, but evidence specifically for SAD is sparse; therefore, omega-3s are a reasonable adjunctive option in people with SAD who want a nutritional approach, provided they’re counseled on limitations and safety. BioMed Central