When the average person thinks of vitamin C, thoughts of oranges, the common cold or immune function might arise—but scientific research has done a lot to expand our knowledge of vitamin C beyond all that. An understanding of what vitamin C is, why we need it and how it works can help you maximize all of its potential benefits.
What is Vitamin C?
Also known as ascorbic acid, vitamin C is part of the water-soluble group of vitamins, of which the eight B-complex vitamins are also members. Vitamin C is dissolved in the watery portions of our foods and is transported into our bloodstream after digestion. Our body then takes the circulating vitamin C and concentrates it, mainly in our white blood cells, eyes, specific hormone-producing glands and brain. Because our kidneys filter the contents of our bloodstream, vitamin C ends up being filtered, too, and any excess is eliminated in the urine, according to the National Institutes of Health (NIH).
How Does the Body Use Vitamin C?
Although conclusive research on vitamin C is elusive, certain functions of vitamin C at the molecular level are unquestionable.
First, vitamin C is necessary for a host of biosynthetic processes. It’s essential for making collagen, a key component of the connective tissue that forms cartilage, bones, teeth and blood vessels; helping heal wounds; and making L-carnitine, a molecule involved in fat metabolism, noted an NIH fact sheet on vitamin C.
Certain neurotransmitters, such as serotonin and norepinephrine, rely on vitamin C for their synthesis as well, according to articles in Pakistan Journal of Nutrition and Brain Research Bulletin. Serotonin is famous for improving mood stability and helps regulate sleep and appetite; norepinephrine plays a role in metabolism and stress.
Outside of its biosynthetic roles, vitamin C is known to support our immune defenses and protect against oxidative damage, functions supported by the results of research published in 2010 in The American Journal of Clinical Nutrition. Vitamin C, along with zinc, plays a vital role in optimizing the function of our white blood cells, which respond to and control infections. Like vitamin E, vitamin C acts as a powerful antioxidant that can combat the oxidative damage of harmful free radicals, even helping renew vitamin E pools. Additionally, vitamin C aids in the absorption of non-heme iron, the only form of the trace mineral present in plant-based foods.
What Are Some of the Benefits of Vitamin C?
Well before vitamin C was discovered in the 1930s, people had become attuned to something in citrus fruits that prevented scurvy, a connective tissue disease that afflicted millions of sailors between the years 1500 and 1800. In the 1970s, Nobel Laureate Linus Pauling promoted megadoses of vitamin C as a way to cure colds and cancer, which catapulted the baby boomer generation into widespread vitamin use.
The honest truth is that outside of preventing scurvy, research on the health benefits of vitamin C is inconclusive. Many researchers have classified the past three decades of related research to be fraught with a lack of scientific rigor, so current research is attempting to distinguish true findings from errors and provide explanations for new discoveries.
Cold Prevention and Treatment
The argument that vitamin C can prevent or treat colds, for example, has been largely refuted in research. Research evidence suggests that megadosing, or taking large amounts of vitamin C, right when cold symptoms begin, does not work better than taking a placebo. A 2002 cohort study in Epidemiology involving more than 4,000 subjects found that “Intake of vitamin C and zinc was not related to the occurrence of common cold,” according to the study’s authors.
Even to perhaps shorten the length of cold symptoms by half a day, research shows that close to 1,000 milligrams of vitamin C would have to be taken regularly, each day—for several months, according to a 2007 research review in Cochrane Database of Systematic Reviews.
Some scientists believe that because vitamin C is known to be involved in immune function and the production of stress-related hormones, that it can benefit people who have weakened immune systems as a result of stress. From research, we know that alcoholics, smokers and obese individuals—people with high levels of stressful insults to their systems—do have a higher risk of vitamin C deficiency.
One such study, published in the American Journal of Clinical Nutrition, compared adult male smokers and nonsmokers with matched dietary intake of antioxidants, and found decreased levels of vitamin C in the group who smoked. However, the research into this area is fairly new—and how the deficiency is related to those conditions is still unknown.
The issue of vitamin C’s antioxidant capabilities is also an interesting quandary. Ongoing research is trying to clarify whether vitamin C can prevent certain chronic diseases such as cancer, cardiovascular disease and arthritis by protecting against free radical buildup. Oxidative damage does play a critical role in these conditions. This information is to be taken with caution, though; Pauling died of cancer (at age 93) despite daily megadoses of vitamin C, and again, the research on chronic disease prevention is fairly nascent.
Though this condition is rare in the U.S., scurvy is a direct result of inadequate vitamin C intake, according to an article published in the American Journal of Public Health in 2004. Its first symptom can simply be fatigue, although scurvy’s most distinctive symptoms are due to general connective tissue weakness manifested as blood vessel fragility, poor wound healing, bleeding from the gums and yellow skin from anemia.
Other Areas of Research
Current research on vitamin C includes studies looking at preventing or slowing macular degeneration, often an age-related eye disease with a pathological process that involves oxidative damage. High blood pressure and stroke risk, although still representing conflicting areas of research, are also popular vitamin C-related research topics due to vitamin C’s possible role in preventing oxidative damage that leads to blood vessel plaques.
Vitamin C’s relationship to aging skin is also being examined. In a study of more than 4,000 women age 40 to 74, vitamin C was linked to better skin elasticity, possibly due to increased collagen production in the skin (Journal of the American Academy of Dermatology, 2003).
How Much Do You Need?
To prevent vitamin C deficiency, the National Academy of Sciences recommends 90 and 75 mg of vitamin C per day for adult men and women, respectively. Most likely, you are among the roughly 85 percent of U.S. adults who already get enough vitamin C. For vitamin C to reduce the risk of atherosclerosis, arthritis and macular degeneration, research studies have typically used a dosage of at least 500 to 1,000 milligrams per day, according to the NIH fact sheet mentioned previously.
How Much Is Too Much?
As mentioned, our kidneys generally regulate the concentration of vitamin C in our bodies. However, 2,000 milligrams per day is the established tolerable upper intake level for vitamin C before adverse events like nausea and diarrhea can appear. Too much vitamin C can also affect how readily certain medications dissolve in urine and can alter the extent to which drugs remain active, the NIH fact sheet also noted. Furthermore, absorption of copper, an essential trace mineral like iron, can be limited by the amount of vitamin C ingested.
Where to Find Vitamin C
Humans, unlike other animals, cannot make vitamin C ourselves, so we need to constantly replenish our bodily stores. These are some of the foods cited by the National Institutes of Health as excellent sources of vitamin C:
- Citrus fruits
- Kiwi fruit
- Strawberries, raspberries, blueberries
- Broccoli, Brussels sprouts, cauliflower
- Green and red peppers
- Spinach and other leafy greens
- Sweet and white potatoes
- Winter squash
Because vitamin C is a highly volatile compound, oxygen, heat and light can speed up how quickly it is oxidized and reduce how long it stays effective. Therefore, foods rich in vitamin C are best eaten raw, without exposure to heat from cooking, according to the Journal of the Science of Food and Agriculture. Also, to maximize vitamin C’s lifespan, vitamin C supplements and fruit juices should be stored in cool places in opaque, airtight containers.
Ultimately, a balanced diet with a full nine servings of fruits and vegetables is the ideal method for ensuring an adequate intake of vitamins, according to Dietary Guidelines for Americans 2015-2020, a publication of the U.S. Department of Health and Human Services and the U.S. Department of Agriculture. If your diet is lacking in fruits and vegetables, some cereals and other foods and juices are fortified with vitamin C. The best way to know is to check the product labels. For those who need extra help, vitamin C supplements may be an additional option.
Benita Lee has a formal background in public health and attended medical school before joining Labdoor, a company that tests and ranks retail supplements, as editorial director and research consultant. Her experience includes research, health care consulting, community and health infrastructure development in resource-poor settings, and patient care in the U.S. and overseas.