5 Science-Backed Supplements to Strengthen Your Immune System This Fall & Winter

As the days get shorter and colder, our immune systems have to work overtime to keep us healthy. Between holiday stress, lack of sleep, and being indoors more often, it’s no wonder so many people end up catching every cold and flu that goes around.

The good news? You can give your body a little extra support with targeted, science-backed supplements.

Here are my top five immune-support picks from a Naturopathic Functional Medicine perspective — and why they work.

1. Vitamin D₃ – Your Immune System’s “On Switch”

Vitamin D is more than just the “sunshine vitamin.” It activates T-cells, which are the immune cells that detect and destroy invaders. Unfortunately, many of us are deficient — especially in the darker months.

💡 Tip: Ask your provider to check your Vitamin D levels so you can personalize your dose. Always take Vitamin D with a healthy fat (like avocado or olive oil) to boost absorption.

2. Vitamin C – The Classic Immune Hero

Vitamin C is a powerful antioxidant that helps your white blood cells work more efficiently and may shorten the duration of colds.

Most adults do well with 500–1,000 mg daily. Just be aware that very high doses can upset your stomach, so it’s best to spread it throughout the day if you need more.

3. Probiotics – Because 70% of Immunity Lives in the Gut 

Your gut microbiome is one of the biggest drivers of immune health. Probiotics keep your intestinal barrier strong and help your immune system respond appropriately — not too weak, not too reactive.

I love UltraFlora® Immune Booster, which contains specific strains that support respiratory and sinus health. This is a great option if you tend to catch every sniffle.

4. Medicinal Mushrooms & Beta-Glucans – Training for Your Immune Cells

Mushrooms like reishi, maitake, and turkey tail are rich in beta-glucans, compounds that help “train” immune cells to respond more effectively.

One of my go-tos is Host Defense MycoShield Spray — I keep it in my bag and use it when I’m around a lot of people (like running errands or volunteering at school).

5. Viracid by Ortho Molecular – My Travel & Holiday Secret

Viracid is a professional-grade formula that combines zinc, vitamins A & C, elderberry, and echinacea for short-term immune support.

This is my personal favorite before, during, and after airplane travel — and yes, I’ve even given it as a stocking stuffer!

Quality Matters – Where to Find These Supplements

Not all supplements are created equal. I recommend using trusted, professional-grade products so you know you’re getting what’s on the label — and nothing you don’t want.

You can find all my immune support favorites in my online Fullscript dispensary, shipped straight to your door.

👉 Order Your Immune-Support Supplements on Fullscript