5 Facts You Need to Know About Vitamin C, According to an Expert in Nutritional Immunology

5 Facts You Need to Know About Vitamin C, According to an Expert in Nutritional Immunology

Immunity is top of mind for us all, and for good reason. From the social distancing, mask-wearing, sanitizing, and proper hand-washing to attempting to get more sleep, exercise, and bolstering our diets with nutrient-dense foods, everyone can agree that keeping our bodies in check is more important than ever before.

But before we start topping our pancakes with elderberry syrup and replacing water with Emergen-C, let's get our facts straight (so we can focus our eating-for-immunity efforts on the methods that are most effective).

vitamin c foods: citrus fruit slices
vitamin c foods: citrus fruit slices

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We spoke with Megan Meyer, PhD in microbiology and nutritional immunology and director of science communication at the International Food Information Council, about one of the most well-known immune-boosting vitamins: vitamin C. Here's everything you should know about vitamin C and immunity, including how it works and what foods are the best sources of vitamin C.

What Does Vitamin C Do for You, Exactly?

"Vitamin C is a water-soluble vitamin that acts as a potent antioxidant," explains Meyer. "It plays an important role in the nervous system, metabolism, and immunity." Additionally, vitamin C helps with micronutrient absorption, especially iron.

How Much Vitamin C Do We Need a Day?

According to Meyer, the recommended dietary allowances (RDAs) for vitamin C range from 15 milligrams to 120 milligrams per day, depending on age and gender. The RDA is also increased if you are pregnant and/or breastfeeding. To see the specific RDAs, check out this article.

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"Also of note: vitamin C used to be listed on the nutrition facts label but is no longer required since, on average, most Americans consume enough vitamin C each day," Meyer says.

Will Doubling Down on My Vitamin C Consumption Help My Immune System?

"Vitamin C is an important nutrient for optimal immune function," says Ali Webster, PhD, RD, director of research and nutrition communications for the International Food Information Council. "However, studies have shown that taking megadoses of it in supplement form doesn't actually do us any good when it comes to fighting off illnesses, like the common cold." According to Webster, more vitamin C isn't necessarily better, because our bodies can absorb only a few hundred milligrams of it at a time. The recommended dietary allowance (or RDA), which is the daily amount of a nutrient that meets the needs of most people, is set at 75 milligrams per day for adult females and 90 milligrams per day for adult males. "Any amount above this is excreted in the urine."

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Does That Mean You Can't Overdose or Take Too Much Vitamin C?

Unlikely, but it still doesn't make chugging Emergen-C five times a day worth it. "Since vitamin C is water-soluble, it has low toxicity and is not linked to adverse effects at high doses," says Meyer. "However, the Food and Nutrition Board at the Institute of Medicine of the National Academies has established a Tolerable Upper Intake Level (aka UL) for vitamin C, stating that long-term intake of vitamin C above this amount may increase the risk of adverse health effects." Similar to the RDAs Webster shared above, your body's UL depends on your age and gender. To find the specific UL for you, see here.

However, if you're taking certain medications, you'll need to be extra cautious with vitamin C supplements. "Vitamin C supplements may interact with several types of medications such as statins, chemotherapy, and radiation," Meyer adds. "Regardless of your medical history and dosages, everyone should be sure to consult with their healthcare provider before taking vitamin C supplements."

What Are the Best Vitamin C Foods to Eat?

According to Meyer, high amounts of vitamin C can be found in vegetables (such as broccoli, Brussels sprouts, cabbage, cauliflower, potatoes, spinach, and tomatoes), citrus fruits and citrus juice, strawberries, and tomato juice. Find our complete explainer on foods that pack the most vitamin C here.