Can Vitamin D Help Prevent Colds and Flu?

Can Vitamin D help your immune system fight back against cold and flu viruses? Our RD dives into this essential nutrient and its role in immune health.

With cold and flu season in full swing, you may be looking for ways to help your body stay healthy or get back to healthy–fast. And that means giving your immune system lots of love. One way you may be able to support your immune system is to ensure you’re not deficient in a very crucial nutrient:

Vitamin D.

Truth is, most Americans are lacking in vitamin D all year round, not just in cold and flu season.

What is Vitamin D?

Vitamin D is a fat-soluble vitamin, meaning the body stores it in fat.

Vitamin D is naturally occurring in some foods and our body can synthesize its own vitamin D. When our skin is exposed to UV light, it triggers vitamin D synthesis in the body. When we are getting less sun exposure, or we are wearing protective UV blocking sunscreen, it can be hard to get all the D we need.

How Does Vitamin D Work?

Vitamin D is most famous for helping promote calcium absorption in the body. Our bodies need vitamin D in order to “unlock,” absorb and use calcium effectively. Without vitamin D, we are susceptible to things like rickets, bone softening or osteopenia, osteoporosis, and brittle bones.

But vitamin D does more than just help our bones stay strong. Some evidence suggests that it may prevent certain cancers. Additionally, early research shows it even can play a role in cognitive function and psoriasis.

Vitamin D receptors are present in immune cells and vitamin D supplementation studies have shown beneficial effects of vitamin D on immune function. Sufficient levels of Vitamin D can reduce your risk of infectious disease by strengthening your innate immune system and turns on key peptides in your immune system that trigger an anti-microbial response that can allow you to fight off invaders before they develop into a full-blown infection.

How Much Vitamin D Do You Need?

A 2005-2006 NHANES (National Health and Nutrition Examination Survey) found an average intake of vitamin D was around 144-276 IU per day, way below our needs!

The general recommendations for vitamin D needs are:

  • Healthy adults ages 14 through 70: 600 IU or 15 mcg daily
  • Kids ages 1-13: 600 IU or 15 mcg daily
  • Older adults over the age of 70:800IU or 20 mcg daily

Exclusively breastfed babies often need supplemental vitamin D, too. As always, check with your healthcare provider before starting any supplement regimen for you or your family members.

How to Get More Vitamin D

Sun Exposure

Your body can synthesize Vitamin D from sun exposure. But when the weather is cooler, days are shorter, or you spend most of the day inside, getting enough Vitamin D from the sun can be difficult.

Food Sources

Vitamin D is found naturally in many foods:

  • Salmon: about 447 IU in 3oz
  • Tuna: about 154 IU in 3oz
  • Fish liver oil: about 1360 IU in 1 tablespoon
  • Beef liver: about 42 IU in 3oz
  • Eggs: about 41 IU in 1 egg

Many Americans do not consume enough of those vitamin D rich foods. In response to a national D deficit, many foods are fortified with vitamin D. Commercially available dairy milk is fortified with D. Most dairy alternative beverages are also fortified with D, but always read the label to be sure. Vitamin D is also found in many ready to eat breakfast cereals.

Vitamin D Supplements

Supplements are plentiful in pharmacies, supermarkets, big box stores, even customized on the internet and can offer an easy way to get more Vitamin D.

Supplements aren’t regulated in the same way pharmaceutical products are. To be sure you are getting a quality product, do your research before trying a new supplement. Look for “USP” on the label. The U.S. Pharmacopeial Convention independently evaluates supplements for purity, potency, and quality. Products must pass their test before they can put the seal on their packages.

After finding a quality product, you may notice vitamin D2 and vitamin D3 are widely available. There are very few differences, some of which are very important to adopters of the vegan lifestyle.

  • Metabolism of D2 and D3 is nearly identical
  • D2 and D3 are both effective at raising blood serum vitamin D levels
  • D2 is ALWAYS vegan-friendly; it’s made from UV irradiation of yeast
  • D3 is sometimes ok for vegans, but not always
    • D3 is made from the conversion of naturally occurring cholesterol
    • It can be made from lanolin, from sheep, or lichens.
  • Vegans should read the label closely before choosing their D supplement

As cold and flu season is in full swing, be sure you’re not lacking in a nutrient that can help your immune system work optimally to help you stay healthy and well. Whether you’re getting your Vitamin D from sunlight, food sources, or supplements, avoiding a deficiency is key for optimal health.

Justine Hays, MS, RD, CDN
Hi! I'm Justine Hays, a registered dietitian, and wellness writer. Food, and memories of food, shaped my life early on, so did my drive and desire to help people. After getting a B.S. in business and marketing, I found my heart wasn't totally satisfied by what I was doing. So, I went back to school and earned my Masters in Dietetics and became a registered dietitian. Working with the general public, I see how much information (and misinformation) is out there. It can be overwhelming! Understanding the facts about food, and how foods work in our bodies, helps us let go of myths and fear so we can get back to enjoying food that nourishes our bodies. That's why I believe in letting experts, like dietitians, deliver the straight answers. I can help you understand what works, what doesn't, why, and how you can make choices to live your healthiest and happiest life. I believe in a whole food approach, meaning everything in moderation. As a working mother, I don't want to spend all my time in the kitchen when there are pictures to paint, flowers to pick, and playgrounds to explore. I find ways to prepare most of my foods from scratch with a healthy dose of convenience foods to make it easier. I prep, plan, and produce (mostly) healthy and affordable meals the whole family will eat, with a sweet treat thrown in the mix for balance, and I always look for ways to get the littlest hands involved in the kitchen. For more information about me and what I do, and for ways to communicate health value with your customers, or to work with a registered dietitian for yourself, your practice, product, website, or blog, please visit and get in touch!