Vitamins C and D: Their Effect on Your Immune System and the Proper Dosage for Your Family

We’ve all been there. Home from school as kids, blowing our noses and coughing up a storm, when mom walks in, pours us a glass of orange juice and tells us to drink up. The logic is sound; one cup of 100% orange juice has 124 mg of vitamin C, well above the recommended daily allowance of 90 mg for adult men and 75 mg for adult women. And while that OJ won’t cure your cold – or prevent it in the first place – studies have shown that it can reduce its duration and severity.

Newer research, however, shows vitamin D is just as important to a healthy immune system as vitamin C. Vitamin D is known as the “sunshine vitamin” because 50 to 90% of the vitamin D in our bodies is produced from exposure to sunlight, but with more and more people working indoors, avoiding the sun or wearing sunblock to ward off skin cancers, vitamin D deficiency has reached epidemic status worldwide. A 2011 study showed over 41% of Americans are deficient, with numbers increasing to 69% in Hispanics and 82% in African Americans.

Very recent research, done at Trinity College in Dublin and reported in April of this year, stated vitamin D deficiency plays an important role in the severity of COVID-19 infections. This mirrors previous research showing low vitamin D levels to be associated with frequent colds and influenza; a 2017 review of research found the odds of contracting a respiratory infection are reduced by 42% if vitamin D levels are sufficient.

Vitamin D also stimulates production of antimicrobial peptides, which means it has an antibiotic effect and can protect against infection. Not to mention it affects the body’s ability to activate T cells; T cells are a specific type of lymphocyte, or white blood cell, that can directly kill both virus-infected cells and cancer cells.

Vitamin C also affects the growth and function of immune cells and antibody production. It encourages the production of white blood cells, notably lymphocytes and phagocytes, which help protect the body against infection. It also helps these white blood cells function more effectively while protecting them from damage from free radicals. However, it is worth pointing out that while you have likely noticed the vitamin aisle in your local drugstore has been cleaned out of vitamin C during the COVID-19 pandemic, and it is true that doctors are experimenting with high-dose IV injections of vitamin C to treat COVID-19 patients, there is, as of yet, no evidence that vitamin C can treat or slow the virus. And even if it could, it would be unwise to take such a large dose of an oral supplement.

Dosage of Vitamin C

Vitamin C is an essential vitamin, which means the body does not produce it on its own; we have to take it in through food and supplements. The National Institutes for Health sets the RDA for vitamin C for adult men at 90 mg and adult women at 75 mg, but as nutritionist Jenn Gargiulo, RDN, CSSD, points out, the RDA is the bare minimum needed to prevent disease.

Vitamin C is also water soluble, which means that while vitamin C is carried to the body’s tissues, it is not stored in the body, so it must be consumed every day. If you consume more than your body needs, it is excreted in your urine. But if you consume too much – upwards of 2000 mg per day – it can cause diarrhea, nausea, stomach cramps or even kidney stones. “I recommend a higher dose than the RDA, especially for athletes and those susceptible to a lot of colds, but not a mega-dose,” Gargiulo says. “500 or 1000 milligrams in a split dose, half in the morning and half in the afternoon, it great for absorption.”

Dosage of Vitamin D

It is wise to have your vitamin D levels checked by your doctor at your annual physical, and if they come back low, you can load up on fatty fish like salmon or fortified dairy products. However, because of the ubiquitous nature of vitamin D deficiency, Gargiulo recommends everyone take a supplement and, as with vitamin C, that they take more than the RDA of 600 to 800 IU daily.

“I recommend 2000 IU per day, and if your levels are really low, you can get a therapeutic dose through a prescription from your doctor,” says Gargiulo, who also points out that in addition to strengthening the immune system, vitamin D reduces the risk of osteoporosis and bone fractures, helps the body transport calcium and, for athletes, can increase physical strength.

Unlike vitamin C, vitamin D is fat-soluble, which means it only dissolves in lipids, and requires the presence of fat to be properly absorbed and carried into the bloodstream. So, if you’re taking your vitamin D on an empty stomach or with your morning coffee, it will not be absorbed and stored for later use. To reap its benefits, try taking your vitamin D supplement with a few tablespoons of peanut butter or your morning eggs.