Vitamin C and the Immune System: Do You Really Need More Vitamin C When You're Sick?

Debunking the Vitamin C Myth: What Really Supports Your Immune System

Why gut health, vitamin D, and daily habits matter more for strong immunity.

Every winter, vitamin C flies off the shelves. Parents stock up for their kids, adults take extra at the first tickle in their throat, and supplements become a daily ritual. But does taking more vitamin C actually boost your immune system when you’re sick?

The short answer: not really. The longer answer tells us a lot about how immune myths spread—and what actually works to support your immune system, especially as we head out of winter and look to rebuild stronger foundations.

Where the Vitamin C Myth Began

The belief in “megadoses” of vitamin C dates back to the 1970s, when Nobel Prize winner Linus Pauling published a book claiming high doses could prevent and treat the common cold. The idea stuck, sales skyrocketed, and vitamin C became a cultural go-to for colds and flus. An "easy fix".

But as immunologist Daniel M. Davis explains in Self-Defense: A Myth-Busting Guide to Immune Health, the immune system is far more complex than a single nutrient. Decades of research since Pauling’s claims show that extra vitamin C doesn’t stop most people from getting sick. At best, it might shorten the length of your cold by just a few hours — if at all.

What Science Actually Says About Vitamin C

• Prevention: For most people, taking vitamin C daily doesn’t reduce the chance of catching a cold.

• Treatment: Starting vitamin C after you get sick hasn’t been shown to make colds shorter or milder.

• Regular intake: People who take moderate amounts of vitamin C daily may experience slightly shorter colds, but the effect is small.

• Special cases: Athletes under extreme stress (like marathon runners in cold weather) might benefit more—but this doesn’t apply to everyday life.

In short: Vitamin C is essential for health, but megadoses when you’re sick won’t “supercharge” your immunity.

The Real Foundation: Gut Health and Daily Habits

Did you know that around 70% of your immune system is connected to your gut? A healthy gut microbiome plays a crucial role in training and regulating your immune defences.

How to support gut-immune health:

• Eat a variety of fibre-rich foods (whole grains, legumes, fruits, vegetables, nuts, seeds).

• Include fermented foods such as yoghurt, kefir, kimchi or sauerkraut, if tolerated.

• Build balanced meals daily—not just when you’re unwell.

• Prioritise sleep, movement, and stress support, which all influence your immune response.

  
  

For kids, this is especially important. A gut-friendly diet helps set up their immune system for long-term resilience—not just to “fight bugs” in winter, but to thrive all year round.

My go-to once a week during cold season is a nourishing bone broth soup or stew — a simple, delicious way to get as much goodness into my family’s bodies to help build strong immune systems.

Vitamin D: The Quiet Immune Helper

Unlike vitamin C, vitamin D does have some evidence supporting its role in reducing respiratory infections—especially in people who are deficient. During New Zealand winters, lower sunlight exposure means vitamin D levels can drop, particularly in:

• Children

• People with limited sun exposure

• People with darker skin

• Older adults or those who cover up for cultural or health reasons

  
  

For most, daily moderate doses (e.g. 400–1000 IU) are more effective than occasional high doses. Vitamin D isn’t a cure-all, but for those at risk of deficiency, it can play a helpful role in immune support. It’s always best to check with your GP before starting supplements, especially for kids.

Building Your Family’s Immune Resilience After Winter

As we move out of the colder months, this is the perfect time to focus on rebuilding your immune foundations—for both adults and children. Instead of relying on quick-fix supplements during illness, think about how daily nutrition, gut health, and vitamin D status set the stage for a stronger immune system year-round.

Practical steps for the months ahead:

• Re-establish regular meal patterns after winter disruptions.

• Boost variety with seasonal spring produce.

• Focus on gut-friendly family meals.

• Get outside daily for sunlight and movement.

• Review vitamin D needs with your healthcare provider if relevant.

Ready to Strengthen Your Immune System Naturally?

If you or your child have been sick on repeat this winter, now is the time to build resilience from the inside out. Through evidence-based nutrition, gut health support, and tailored plans, I can help you create a strategy that supports your family’s immune health all year.

👉 Book a consultation with SuccessFuel Nutrition to build your post-winter immune support plan.