It’s Fine to Take Vitamins C and D to Help Boost Your Immune System—By Dr. Fauci. Here’s What to Know

“If you’re deficient in vitamin D, that does have an impact on your susceptibility to infection,” said Dr. Fauci, director of the National Institute of Allergy and Infectious Diseases. “I would not mind recommending, and I do it myself, taking vitamin D supplements.” But that’s not all: Dr. Fauci also recommended another vitamin. “The other vitamin that people take is vitamin C because it’s a good antioxidant, so if people want to take a gram or so of vitamin C, that would be fine,” he said.

How can vitamin D help boost your immune system?

Backing up a second here: Vitamin D, aka calciferol, is a fat-soluble vitamin that’s naturally present in a few foods, like fatty fish, beef liver, cheese, and egg yolks, per the National Institutes of Health Office of Dietary Supplements (NIH). It’s produced in your body when UV rays from the sun hit your skin and trigger what’s known as vitamin D synthesis.

Vitamin D can do a slew of different things in your body, including strengthen your bones, reduce inflammation, and help with immune function, the NIH says.

Here’s the big reason why vitamin D can be helpful as a supplement, per Dr. Adalja: Some people are deficient in it, meaning they don’t get enough of it on a regular basis. (An NIH data analysis specifically found that about 18% of people are at risk of having inadequate levels of vitamin D, while 5% are at risk of having an actual deficiency.)

As for the link with immune function, one systematic review and meta-analysis of data from 11,321 people published in the BMJ found that people took weekly or daily supplements of vitamin D were less likely to develop respiratory tract infections than those who didn’t. People who were the most deficient in vitamin D had the biggest benefit.

Another systematic review and meta-analysis of 5,660 people published in PLOS One found that vitamin D supplementation had a “protective effect” against respiratory tract infections, with a daily dose being the most effective.

Foods that contain Vitamin D


Few foods naturally contain vitamin D. The flesh of fatty fish (such as trout, salmon, tuna, and mackerel) and fish liver oils are among the best sources [17,1]. An animal’s diet affects the amount of vitamin D in its tissues. Beef liver, cheese, and egg yolks have small amounts of vitamin D, primarily in the form of vitamin D3 and its metabolite 25(OH)D3. Mushrooms provide variable amounts of vitamin D2 [17]. Some mushrooms available on the market have been treated with UV light to increase their levels of vitamin D2. In addition, the Food and Drug Administration (FDA) has approved UV-treated mushroom powder as a food additive for use as a source of vitamin D2 in food products [18]. Very limited evidence suggests no substantial differences in the bioavailability of vitamin D from various foods [19].

Animal-based foods typically provide some vitamin D in the form of 25(OH)D in addition to vitamin D3. The impact of this form on vitamin D status is an emerging area of research. Studies show that 25(OH)D appears to be approximately five times more potent than the parent vitamin for raising serum 25(OH)D concentrations [17,20,21]. One study found that when the 25(OH)D content of beef, pork, chicken, turkey, and eggs is taken into account, the total amount of vitamin D in the food is 2 to 18 times higher than the amount in the parent vitamin alone, depending on the food [20].

Fortified foods provide most of the vitamin D in American diets [1,22]. For example, almost all of the U.S. milk supply is voluntarily fortified with about 3 mcg/cup (120 IU), usually in the form of vitamin D3 [23]. In Canada, milk must be fortified with 0.88–1.0 mcg/100 mL (35–40 IU), and the required amount for margarine is at least 13.25 mcg/100 g (530 IU). Other dairy products made from milk, such as cheese and ice cream, are not usually fortified in the United States or Canada. Plant milk alternatives (such as beverages made from soy, almond, or oats) are often fortified with similar amounts of vitamin D to those in fortified cow’s milk (about 3 mcg [120 IU]/cup); the Nutrition Facts label lists the actual amount [24]. Ready-to-eat breakfast cereals often contain added vitamin D, as do some brands of orange juice, yogurt, margarine, and other food products.

The United States mandates the fortification of infant formula with 1–2.5 mcg/100 kcal (40–100 IU) vitamin D; 1–2 mcg/100 kcal (40–80 IU) is the required amount in Canada [1].

A variety of foods and their vitamin D levels per serving are listed in Table 3.

Food*Micrograms
(mcg) per
serving
International
Units (IU)
per serving
Percent DV*
Cod liver oil, 1 tablespoon34.01,360170
Trout (rainbow), farmed, cooked, 3 ounces16.264581
Salmon (sockeye), cooked, 3 ounces14.257071
Mushrooms, white, raw, sliced, exposed to UV light, ½ cup9.236646
Milk, 2% milkfat, vitamin D fortified, 1 cup2.912015
Soy, almond, and oat milks, vitamin D fortified, various brands, 1 cup2.5-3.6100-14413-18
Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 1 serving2.08010
Sardines (Atlantic), canned in oil, drained, 2 sardines1.2466
Egg, 1 large, scrambled**1.1446
Liver, beef, braised, 3 ounces1.0425
Tuna fish (light), canned in water, drained, 3 ounces1.0405
Cheese, cheddar, 1 ounce0.3122
Mushrooms, portabella, raw, diced, ½ cup0.141
Chicken breast, roasted, 3 ounces0.141
Beef, ground, 90% lean, broiled, 3 ounces01.70
Broccoli, raw, chopped, ½ cup000
Carrots, raw, chopped, ½ cup000
Almonds, dry roasted, 1 ounce000
Apple, large000
Banana, large000
Rice, brown, long-grain, cooked, 1 cup000
Whole wheat bread, 1 slice000
Lentils, boiled, ½ cup000
Sunflower seeds, roasted, ½ cup000
Edamame, shelled, cooked, ½ cup000

* DV = Daily Value. The FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for vitamin D on the new Nutrition Facts and Supplement Facts labels and used for the values in Table 3 is 20 mcg (800 IU) for adults and children aged 4 years and older [26]. The new labels must list vitamin D content in mcg per serving and have the option of also listing the amount in IUs in parentheses. FDA required manufacturers to use these new labels starting in January 2020, but companies with annual sales of less than $10 million may continue to use the old labels that list a vitamin D DV of 400 IU until January 2021 [28,29]. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.
** Vitamin D is in the yolk.

How can vitamin C help boost your immune system?

While Dr. Adalja says that there’s “more data for vitamin D,” there is some research to support taking vitamin C supplements, too. In case you’re not familiar with it, vitamin C is a water-soluble vitamin that’s naturally present in some foods, like oranges, strawberries, broccoli, and tomatoes, per the NIH. Also known as L-ascorbic acid, it’s an antioxidant that “plays an important role in immune function,” the NIH says.

One review and meta-analysis conducted by researchers at Cochrane found that people who took vitamin C supplements when they had a cold had the infection reduced by 8% in adults and 14% in children. (That translated to about a day less of dealing with a cold.) People who took vitamin D supplements also had less severe colds than those who didn’t.

Vitamin C supplements may also help if you tend to exercise a lot. One Cochrane review looked at data on 642 marathon runners, skiers, and soldiers who took vitamin C supplements and found that taking anywhere from 250 milligrams to 1 gram a day of the vitamin reduced the risk of developing a cold by 50%.

Sources of Vitamin C

Food

Fruits and vegetables are the best sources of vitamin C (see Table 2) [12]. Citrus fruits, tomatoes and tomato juice, and potatoes are major contributors of vitamin C to the American diet [8]. Other good food sources include red and green peppers, kiwifruit, broccoli, strawberries, Brussels sprouts, and cantaloupe (see Table 2) [8,12]. Although vitamin C is not naturally present in grains, it is added to some fortified breakfast cereals. The vitamin C content of food may be reduced by prolonged storage and by cooking because ascorbic acid is water soluble and is destroyed by heat [6,8]. Steaming or microwaving may lessen cooking losses. Fortunately, many of the best food sources of vitamin C, such as fruits and vegetables, are usually consumed raw. Consuming five varied servings of fruits and vegetables a day can provide more than 200 mg of vitamin C.

FoodMilligrams (mg) per servingPercent (%) DV*
Red pepper, sweet, raw, ½ cup95106
Orange juice, ¾ cup93103
Orange, 1 medium7078
Grapefruit juice, ¾ cup7078
Kiwifruit, 1 medium6471
Green pepper, sweet, raw, ½ cup6067
Broccoli, cooked, ½ cup5157
Strawberries, fresh, sliced, ½ cup4954
Brussels sprouts, cooked, ½ cup4853
Grapefruit, ½ medium3943
Broccoli, raw, ½ cup3943
Tomato juice, ¾ cup3337
Cantaloupe, ½ cup2932
Cabbage, cooked, ½ cup2831
Cauliflower, raw, ½ cup2629
Potato, baked, 1 medium1719
Tomato, raw, 1 medium1719
Spinach, cooked, ½ cup910
Green peas, frozen, cooked, ½ cup89

*DV = Daily Value. The U.S. Food and Drug Administration (FDA) developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for vitamin C on the new Nutrition Facts and Supplement Facts labels and used for the values in Table 2 is 90 mg for adults and children age 4 years and older [14]. FDA required manufacturers to use these new labels starting in January 2020, but companies with annual sales of less than $10 million may continue to use the old labels that list a vitamin C DV of 60 mg until January 2021 [13,15]. FDA does not require the new food food labels to list vitamin C content unless vitamin C has been added to the food. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.

Recommended Intakes

Intake recommendations for vitamin C and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine (IOM) of the National Academies (formerly National Academy of Sciences) [8]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender [8], include:

  • Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
  • Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.
  • Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.
  • Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.

Table 1 lists the current RDAs for vitamin C [8]. The RDAs for vitamin C are based on its known physiological and antioxidant functions in white blood cells and are much higher than the amount required for protection from deficiency [4,8,11]. For infants from birth to 12 months, the FNB established an AI for vitamin C that is equivalent to the mean intake of vitamin C in healthy, breastfed infants.

AgeMaleFemalePregnancyLactation
0–6 months40 mg*40 mg*
7–12 months50 mg*50 mg*
1–3 years15 mg15 mg
4–8 years25 mg25 mg
9–13 years45 mg45 mg
14–18 years75 mg65 mg80 mg115 mg
19+ years90 mg75 mg85 mg120 mg
SmokersIndividuals who smoke require 35 mg/day
more vitamin C than nonsmokers.

So should you take vitamin D and vitamin C supplements?

It’s hard to make a blanket statement that everyone should take a particular supplement, but Richard Watkins, M.D., an infectious disease physician and professor of internal medicine at the Northeast Ohio Medical University, tells Health that these supplements are good for people to consider taking “in general.” And, he says, it’s reasonable for people to take vitamins D and C “in normal amounts” to try to boost your immune system.

Just so you know, the NIH recommends that most healthy adults strive to get 15 micrograms of vitamin D a day, while healthy women should strive to take 75 milligrams of vitamin C, and men should aim for 90 milligrams of the vitamin a day.

Of course, if you’re interested in taking a new supplement, it’s a good idea to check in with your doctor, just in case it could interfere with any other medications you’re taking. But, in general, experts say adding vitamins D and C supplements could be a great thing for your immune system.

Lilian Mike

Author & Founder Healthfitness102

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