How To Boost Your Vitamin D Levels During Cold and Flu Season

A young woman in her room with her face half in sunlight and shadow.


Key Takeaways

  • Vitamin D is a key nutrient that helps support the immune system. You can get it from sunlight, food, and supplements.
  • It can be difficult to get enough vitamin D during cold and flu season if you live in a climate that gets less sunlight during the winter months.
  • You can increase your vitamin D levels by getting sunlight, eating foods rich in vitamin D, or taking a supplement if necessary.

Supporting your immune system involves eating vitamin-rich foods, washing your hands, and getting quality sleep. Research has also shown that vitamin D plays a significant role in keeping your immune system at its best. Studies have shown that being deficient in vitamin D can make you more susceptible to infections.

During cold and flu season—particularly during a pandemic—a strong immune system is one of your best defenses. Here's what you need to know about vitamin D, including how to increase your intake.

What Is Vitamin D?

Although it has "vitamin" in its name, vitamin D is technically a hormone. Unlike many other key nutrients, your body can make vitamin D. When your skin is exposed to the sun for a long enough time, your body can synthesize vitamin D. You can also get it through foods and supplements. Vitamin D deficiency is linked to an increased risk of depression, weaker bones, and fatigue.

Vitamin D and Immune Support

From influenza and the common cold to COVID-19, our immune systems have a lot to contend with these days. While you won't find a single nutrient that can prevent you from getting sick, adequate levels of vitamin D helps your body combat illness.

One cross-sectional study evaluating over 14,000 people found that people with lower serum vitamin D levels had a 58% higher odds of getting an acute respiratory illness (like the common cold) compared to people who had higher levels. 

Researchers have also recently reported that people with a vitamin D deficiency are more susceptible to COVID-19's deadly “cytokine storm” (a dramatic immune system overreaction). Almost 20 data analyses have shown that vitamin D deficiency is a major contributor to COVID-19 risk and severity. 

What This Means For You

Vitamin D is key for a healthy immune system. While you can get it from sunlight, if you live in a place that doesn't get much during the winter months, there are other ways to boost your levels. There are some foods, like milk and eggs, that are naturally rich in vitamin D. Others, like milk and cereal, are fortified. You can also take supplements, if necessary, to prevent deficiency.

How To Support Healthy Vitamin D Levels

The recommended dietary intake of vitamin D is 600 to 800 IU per day for adults, although some experts believe the requirements should be increased. Your healthcare provider can evaluate whether you have a deficiency by conducting a simple lab test. 

There are three ways that you can support a healthy vitamin D level or replenish a diagnosed deficiency:  

  • Ensure adequate sun exposure. Exposure to the sun is key for your body to synthesize vitamin D. But remember to still use sunscreen to protect from the sun's harmful UV affects.
  • Take vitamin D supplements. Any supplementation should be discussed with your doctor before starting a regimen. Choose vitamin D in the D3 form, and not the D2 form when possible
  • Eat vitamin D-rich foods. While the list of foods that contain vitamin D is not extremely long, you have plenty of options—from fish and some vegetables to fortified foods and milk.

Vitamin D-Rich Foods

If you don't live in a climate that gets a lot of sunlight year-round and you'd prefer to avoid taking a supplement, know that you can get some vitamin D from your diet. If you eat animal products, like fish and milk, you'll have even more options. Many foods, like cereal, are fortified with nutrients including vitamin D.


Oily fish like salmon naturally contain vitamin D, along with other immune-supporting nutrients like DHA omega-3 fatty acids. Whether you toss it on a salad or serve it on a bed of rice, salmon can be a great choice for your vitamin D-building diet. 

When selecting your fish, choose sustainably raised options that are naturally low in mercury, like Chilean-farmed salmon.

Fortified Orange Juice

When choosing your OJ—from pulp-free or low acid—look for a bottle that's been fortified with vitamin D, calcium, and other key nutrients.

In addition to the immune-supporting vitamin C naturally provided by orange juice, the vitamin D found in these fortified choices gives the immune system a double-dose of support. 

Dairy Milk

Calcium is often the nutrient that comes to mind when people think about milk, but it's also full of other key nutrients, including vitamin D. Milk also contains vitamin A and protein, two other important nutrients for immune function.

Most milk is fortified with 100-150 IU of vitamin D per 8-ounce serving, providing 15% of the recommended daily value. 

Canned Tuna

Canned tuna is a quick and convenient vitamin D boost. Look for tuna that is packaged in BPA-free containers to minimize your exposure to the potentially harmful chemical.

Certain Mushrooms

As the only source of vitamin D in the produce aisle, mushrooms are able to produce vitamin D after being exposed to UV light (much like humans). 

Portabella, cremini, and white mushrooms top the list, but all mushrooms have at least some vitamin D.

When you're making a hamburger, meatloaf, or other ground beef-based dish, sub half of the meat with chopped mushrooms. The recipe tastes great and packs extra nutrition.

Fortified Cereals

Many popular brands of cereal are fortified with vitamin D, as well as other important nutrients. To get the full vitamin D trifecta for breakfast, combine your cereal choice with milk and a glass of fortified OJ.


Eggs can be a healthy source of vitamin D, as long as you are eating the yolk. Eggs that came from hens that live outside and get plenty of sunlight are especially beneficial. Research has shown that the vitamin D3 content of egg yolk is three-to fourfold higher when the eggs came from outdoor hens versus hens that live indoors.

Beef Liver

If you're a meat-eater, beef liver is a naturally rich source of vitamin D and other important nutrients, like folate. It's also a budget-friendly and versatile protein choice.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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