By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital

Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily

One trend in the nutrition world has been megadosing vitamin C. Some people believe that doing so will lead to optimal health and can even prevent diseases such as cancer. Professor Anding assesses the evidence.

Vitamin C Daily Needs

Vitamin C has a wide range of benefits, including assisting with wound healing, acting as an antioxidant, and helping us to better absorb essential amino acids. There is much debate surrounding how much vitamin C we need each day for optimal health.

The recommended daily allowance (RDA) indicates the amount sufficient to meet the requirements of nearly 98% of healthy individuals in particular life stages and gender groups. Many people believe that the daily value on a vitamin only covers 50% of the population, but that is not true. 

Another myth about interpreting the vitamin label is that if you’re ill, that amount of vitamin is going to cover you. Remember, it covers 98% of healthy individuals. 

“There is no daily requirement for individuals who are ill, and I think that’s where some of the issues come in,” Professor Anding said. 

Requirements can change throughout a person’s life cycle, and depends on their level of health. For example, if you have had a significant burn, you might need extra vitamin C to repair the damage.

Some people believe you need up to 2,000 milligrams of vitamin C per day. The RDA for health individuals is actually much less, though.

Males in the age range of 19 to 90 require about 90 milligrams; females in the same age group require 75 milligrams. When combining fruits and vegetables, it’s not too difficult to meet those requirements.

Cancer Prevention and Vitamin C

The National Cancer Institute (NCI) has issued a position, backed by more than 150 studies, that people who eat plenty of fruits and vegetables develop less cancer, including a number of different types of cancers. The NCI encourages the consumption of five or more servings of fruits and vegetables daily.

What’s in fruits and vegetables that’s contributing to this reduced cancer risk? Many people believe that because fruits and vegetables are a major source of vitamin C, it must be the vitamin C. 

“Over and over again in clinical nutrition, we’ve made that quantum mistake,” Professor Anding said. “We believe it’s one compound in fruits and vegetables—in this case, vitamin C—that’s responsible for the reduced risk of disease. That’s not the case.”

Additionally, the United States Department of Agriculture (USDA) recommends two to four servings of fruit and three to five servings of fruits and vegetables daily. Clearly, this is enough to meet the vitamin C requirements. However, interpretations from the NCI and the USDA guidelines always suggest that the vitamin C in fruits and vegetables is the mechanism that protects against cancer. 

“I’m going to suggest to you it’s probably not,” Professor Anding said. “Vitamin C may be an important component in disease risk reduction, but what’s unique about fruits and vegetables?”

Professor Anding recommends that you choose your fruits and vegetables based on the colors of the rainbow. Emerging science suggests that it’s the colors in the plants, rather than the vitamins and minerals in fruits and vegetables, that may actually give you the best disease reduction. 

Some of the supplement studies have consistently fallen short when it comes to demonstrating that vitamins alone—that is, vitamins that are synthetically produced and come in a bottle—are effective at preventing cancer and other chronic illnesses. Food-based research studies and the NCI-based publications suggest that eating more fruit is a much better way to prevent disease.

Special Considerations

Some populations need more or less vitamin C than others, and the need varies with other factors such as health status and lifestyle choices. Individuals engaged in strenuous exercise experience frequent viral infections. 

In fact, we see a spike in viral infections post-marathon. Some studies suggest that daily supplements of 500 to 1,500 milligrams of vitamin C—significantly more than the recommended daily value—may protect against upper respiratory infections in this group.

Those who lead unhealthy lifestyles may also need more vitamin C. Individuals who smoke or experience secondhand smoke need about one and a half times the normal amount. Female smokers need at least 95 milligrams per day and male smokers need at least 110 milligrams per day. 

Therefore, Professor Anding suggests that most individuals will probably do fine with the recommended guidelines for vitamin C, but those with a compromised immune system should take extra. Additionally, it is ideally best to obtain your vitamin C from whole fruits and vegetables rather than supplements. 

This article was edited by Kate Findley, Writer for The Great Courses Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.