Seasonal Depression (SAD): What it is and how to feel better this winter

By Margaret DeCosta

Many people notice that their mood drops when the days get shorter. You might feel more tired, crave carbs, lose motivation, or feel “heavy” during the fall and winter months. If this sounds familiar, you’re not alone. This pattern can be called Seasonal Affective Disorder (SAD), a form of depression triggered by reduced daylight. The good news? There are evidence-based treatments that truly helps. Below is a simple guide you can start using right away, including light therapy, exercise, vitamin D, and what we currently know about red and infrared light.

Why does seasonal depression happen?

Shorter days mean less morning light, which disrupts your circadian rhythm (your internal

clock). This shift can lower serotonin (your mood chemical), alter melatonin (your sleep

hormone), and throw off your overall energy. This is why treatment focuses heavily on getting your brain the type of light it’s missing.

1. Bright Light Therapy: The #1 Proven Treatment

Bright light therapy has been studied for decades and is considered a first-line treatment for SAD.

How to use it

● Use a 10,000-lux light box

● 20–30 minutes every morning, ideally within an hour of waking

● Place the light slightly above eye level, about the distance of an outstretched arm

● Look toward it, but don’t stare directly into it

Many people notice improvements within 1–2 weeks.

What to look for in a device

● Must say 10,000 lux

● Must say UV-free

● Should be a true SAD therapy box (not a regular lamp)

Common side effects

Mild headache, restlessness, or insomnia if used too late in the day. If this happens, shorten the session or move the box farther away.

2. Red Light & Infrared

(Photobiomodulation): What We Know So Far

Many patients ask about red or near-infrared light therapy. These lights are being studied for mood, energy, inflammation, and brain health.

Here’s the truth:

Red/NIR light is promising, but not yet as well-studied for SAD as bright white light.

However, early research on depression (non-seasonal) shows potential benefits, and many patients report improvements in energy and sleep. If you want to try it as an add-on (not a replacement), here’s how to do it safely:

Recommended ranges from clinical research

● Wavelengths:

○ Red light: 630–660 nm

○ Near-infrared: 810–850 nm

● Irradiance (power at the skin):

○ Aim for roughly 10–40 mW/cm2

● Session time:

○ Usually 5–15 minutes depending on device power

These guidelines come from photobiomodulation studies used in clinical research.

Important note about wattage- “Wattage” on the box often means electrical power, not therapeutic power. What matters is irradiance (mW/cm2), which only reputable brands publish.

Should red/infrared replace bright light therapy?

Not yet. Use red/NIR as a bonus option. Bright white light remains the primary treatment for SAD.

3. Vitamin D: Helpful If You’re Low

Vitamin D has mixed research results for seasonal depression. It’s not a cure by itself, but if your levels are low, replacing vitamin D can absolutely help your mood, energy, immunity, and sleep.

What I recommend

● Ask your provider to check your 25-OH vitamin D level

● Most people aim for 2,000 IU daily in winter if they are insufficient

● If levels are very low, a temporary higher dose may be used, but should be supervised

4. Exercise & Outdoor Time

Movement is one of the most powerful antidepressants we have and when you combine

exercise with daylight, results are even better.

Easy ways to start

● 20–30 minutes of walking in the morning

● Outdoor breaks whenever possible

● Resistance training 2–3 times weekly

● Join a class or follow online videos for accountability

Even small, consistent changes improve mood.

5. Sleep, Structure, and Routine

Your brain thrives on rhythm. Especially when the sunlight rhythm is disrupted.

Try:

● Waking up at the same time daily, even on weekends

● Using morning light (box + outdoor light) to “anchor” your clock

● Avoiding screens 1 hour before bed

● Keeping your bedroom dark and cool

6. When Medication Helps

Some people benefit from adding medication, especially if symptoms are more than mild.

Options include:

● Bupropion XL, which is FDA-approved for preventing seasonal episodes

● SSRIs (such as sertraline, escitalopram, fluoxetine)

● Short-term medication support during the winter months

When to Reach Out

You deserve to feel well all year, not just in summer.

Reach out if you notice:

● Persistent sadness

● Loss of motivation

● Oversleeping or low energy

● Increased appetite or cravings

● Withdrawing from people

● Thoughts of self-harm (always seek help immediately)

We can build a personalized plan using therapy, light, supplements, lifestyle support, or

medication, whatever combination helps you thrive during the darker months.

Final Thoughts

Seasonal depression is real, common, and treatable. Light is one of the most powerful tools we have, and when combined with movement, nutrition, routine, and if needed professional support.

References

1. Levitan RD et al., Optimal implementation of bright light therapy. (classic review on

lux/dosing). PMC

2. Yale School of Medicine — Winter Depression / light-box guidance (clinical

implementation). Yale School of Medicine

3. Wang L., Photobiomodulation: shining a light on depression (review of red/NIR PBM

mechanisms & trials). PMC

4. Frandsen TB et al., Vit D RCT in SAD (mixed results / underpowered). PubMed

5. Endocrine Society (2024) clinical guidance on vitamin D—check and correct deficiency

per usual practice. PubMed

6. Noetel M. et al., 2024 systematic review: exercise effective for depression. PubMed

7. FDA label / Wellbutrin XL: approved indication for prevention of seasonal major

depressive episodes. FDA Access Data