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Vitamin C – How Much Do I Need For Immune Benefit Can Megadoses Help?

I was at the drugstore last week to pick up a few household items and I received a text message from my friend “could you buy me some vitamin C, I forgot to get some.” She likely didn’t need any more Vitamin C, I thought to myself, as she was already taking MEND Regenerate (contains 30mg of vitamin C) and eating grapefruits and oranges daily in addition to her vegetarian diet. But during the COVID-19 pandemic, telling someone that they didn’t need something that they believed they needed for their well-being, was not wise. I replied “I’d be happy to” as I made my way over to the vitamin aisle. 

There were empty shelves where vit-c used to sit. It was completely sold out — apparently people were hoarding it, just as they were toilet paper and other essentials. My friend ended up ordering “Emergen-C” on Amazon — a thousand milligram per serving product that has become popular and widely available.

This got me thinking, how much Vitamin C should one be taking regularly and is there any evidence to suggest that temporary megadoses could help to address acute conditions or acute needs (such as revving up the immune system)?

First the basics

There are thirteen vitamins. These are organic molecules referred to as “micronutrients” that are needed in small amounts for the body to work correctly. Vitamins play a very diverse set of biochemical functions from strengthening bones and healing wounds to bolstering the immune system. Vitamins fall into two broad classes: water soluble and fat soluble. As implied by the name, water soluble vitamins dissolve in water and can be easily absorbed into the bloodstream. Fat soluble vitamins are much better absorbed when taken with fat.

Vitamin C is a water soluble essential vitamin that is found in many fruits and vegetables, including: oranges, strawberries, kiwi fruit, bell peppers, broccoli, kale, and spinach. 

It has a role in the repair of tissue, production of certain neurotransmitters, functioning of key enzymes and the immune system, and also acts as an antioxidant. Vitamin C is on the World Health Organization’s List of Essential Medicines, the safest and most effective medicines needed in a health system.

Vitamin C can impact the immune system in many ways. First, it is an antioxidant and can help as adequate amounts of neutralizing antioxidants are required, to prevent damage to the immune cells from the release of reactive oxygen species from phagocytes as they gobble up antigens. Second, it boosts the activity of phagocytes, which are immune cells that can “swallow” harmful bacteria and other particles. Finally, it promotes the growth and spread of lymphocytes, a type of immune cell that increases your circulating antibodies, proteins that can attack foreign or harmful substances in your blood.

How much Vitamin C do I need?

As per the Mayo Clinic, the recommended daily amount for adults is 65 to 90 milligrams (mg) a day, and the upper limit is 2,000 mg a day. Although too much dietary Vitamin C is unlikely to be harmful (as any unused amount is secreted by the body through urine), megadoses might cause diarrhea, nausea, vomiting, heartburn, abdominal cramps, headaches or insomnia.

If you’re eating a balanced diet, you’re likely getting plenty of Vitamin C for your day to day needs. People who are deficient, likely have a poor diet, may have kidney disease, are heavy drinkers or are smokers. If you’re among the 7% of Americans who aren’t getting enough, you’ll notice symptoms in weeks to 3 months. These symptoms include bruising, nosebleeds, bleeding gums, dry skin, weight gain and fatigue.

With 30 mg from her MEND Regenerate smoothie, 50-60 mg from orange and likely a lot more from her vegetarian diet, my friend was getting more than enough from a daily value perspective.

But was there any basis to her taking a megadose to boost her immune system?

Is there Evidence for Megadoses of Vitamin C?

The product my friend purchased contained more than 10x the daily recommended dose. Was there evidence supporting this level of dosing? 

Vitamin C has been studied fairly extensively as it relates to the common cold with studies generally concluding a statistically significant biological effect in reducing the duration and severity of colds. Furthermore, in one study there appeared to be a linear relationship with the duration and severity being reduced more at an 8g/day dose vs. 3g/day dose. It is worth noting however, that each of these studies looked at reduction of cold and not the prevention of a cold. Studies that have looked at the prevention of colds showed no positive effect.

COVID-19 is not the common cold, it’s an infectious disease caused by a new virus that science is still studying. While physicians and researchers are studying the effects of high dose intravenous Vitamin C on the new coronavirus, no supplement can prevent or treat the disease.

So should my friend be megadosing? The answer is unfortunately that there is no conclusive evidence yet that it will provide any benefits against. However given how safe it is and its well studied effects on supporting the immune system, there also doesn’t appear to be any risk in taking megadoses temporarily.