When cold and flu season arrives, the focus turns toward vitamin C in the hope that getting more of it will prevent the common cold and other pesky viral infections. Unfortunately, the evidence that vitamin C prevents colds is weak. Still, getting enough vitamin C is important for a healthy immune system, your body’s defense against cold and flu viruses. But, this doesn’t mean that mega-doses offer additional benefits. In defense of vitamin C and its role in cold prevention, it does based on studies, slightly shorten the duration of a cold. You might feel better a day sooner if you increase your vitamin C intake if you have a vitamin c deficiency.
However, vitamin C is more than a one-trick pony. You need sufficient amounts of it for a variety of functions in the human body including:
· Synthesis of collagen for healthy skin and joints
· To fight oxidative stress
· To prevent a serious disease called scurvy
· To recycle other antioxidants, including vitamin E
· For wound healing
· To help absorb iron from plant-based foods. Vitamin C boosts its absorption
· To synthesize the neurotransmitter norepinephrine
· To make carnitine, an important cellular component for converting fat to energy
Humans, along with primates and guinea pigs, are the only animals that can’t make vitamin C and must get it through diet to avoid a deficiency. The U.S.D.A. recommends that males get a minimum of 90 milligrams of vitamin C daily and women 75 milligrams.
How easy is it to get this quantity of vitamin C through diet? If you eat a large orange each day, you’ll almost meet your vitamin C requirements. But, oranges aren’t the best source of vitamin C. A large orange has around 75 milligrams, but a cup of strawberries has 85 milligrams. Pineapples, mangos, kiwis, and Brussels sprouts are also excellent sources. Most fruits and vegetables contain at least modest amounts of vitamin C. However, cooking can destroy 15 to 55% of the vitamin C content of a vegetable. So, all in all, fruit is a better source of vitamin C because you typically don’t cook it.
Is the Recommended Intake of Vitamin C Too Low?
The vitamin C guidelines were developed to lower the risk of developing scurvy, the classic vitamin C deficiency disease. Before the link between vitamin C and scurvy was discovered, sailors who ate no plant-based foods for many months developed classic symptoms of this disease, bruising, poor wound healing, bleeding gums, and anemia due to vitamin C deficiency. Many of them died. Although the quantity of vitamin C needed to prevent scurvy is lower than the U.S.D.A. recommendations, the guidelines are still based on the amount needed to prevent scurvy, not to maximize health. If you could ask Linus Pauling, he would tell you that you need substantially more. In fact, he himself took mega-doses of vitamin C.
What would be the benefits of getting more? Some studies link diets higher in vitamin C with a lower risk of some types of cancer, but it’s hard to show cause and effect. The reduced risk of vitamin C could be because people who get lots of vitamin C in their diet also eat more fruits and vegetables. Yet we know vegetables and fruits contain other components that help ward off cancer. There’s also some evidence that consuming more vitamin C reduces the risk of age-related eye problems such as age-related macular degeneration and cataracts.
All in all, there’s no strong evidence that getting high doses of vitamin C helps prevent the common cold or other diseases, with the possible exception of age-related eye diseases. But, the recommended daily intake is still on the conservative side as these guidelines are based on the prevention of scurvy. If the link between cancer risk and vitamin C is real, there would certainly be an incentive to get more than the current recommendations. But, at this point, there’s little justification for taking mega-doses or a high dose supplement, especially when fruits and vegetables contain substantial quantities.
Reasons You Might Have a Vitamin C Deficiency
Is vitamin C deficiency common? A 2009 study placed the incidence at around 13%. You might surmise that folks who are deficient don’t eat their fruits and vegetables – likely true, but certain lifestyle habits and medical problems increase your body’s need for vitamin C. For example, smokers have levels, of vitamin C in their tissues, as much as one-third lower than non-smokers. Stress and physical illness also increase the demand for vitamin C since vitamin C is an antioxidant vitamin and gets used up faster when your body is under stress. Athletes may need slightly more as exercise is a form of stress on the body, although taking a vitamin C supplement prior to exercise may interfere with some of the adaptations to exercise, based on some research. If you have certain diseases that reduce absorption of vitamin C, you may become deficient despite consuming vitamin C through diet.
Are There Downsides & Side Effects associated with Increasing Your Vitamin C Intake?
You’re unlikely to have side effects from vitamin C if you consume it exclusively through diet. vitamin C supplement can cause digestive symptoms, like diarrhea. It also stimulates the excretion of oxalate and may boost the risk of oxalate kidney stones. Plus, vitamin C at high doses can interfere with the activity of some medications. The risk of side effects goes up as vitamin C consumption exceeds 500 milligrams daily.
Finally, your body doesn’t take up all of the vitamin C when you take high doses. You absorb it best at between 30 to 180 milligrams daily. As you increase the dose above this daily quantity, absorption drops by as much as half. Since vitamin C is a water-soluble vitamin, the excess is excreted in the urine. So, you lose a portion of the vitamin C you take in and the loss is higher when you consume high amounts.
The Bottom Line
It’s important to get meet the daily recommended value of vitamin C, but since these guidelines were based on preventing scurvy, most of us can benefit from consuming more than the minimum, particularly smokers, athletes, and anyone else under stress – and who isn’t? This doesn’t mean you should take a vitamin C supplement. Instead, get vitamin C from eating 5 or more servings of fruits and vegetables daily and make sure at least one of those servings is a piece of raw fruit. By doing this, you’ll easily get double the recommended amount and will enjoy the other nutrients and phytonutrients that fruits and veggies offer.
Am J Clin Nutr November 2009. vol. 90 no. 5 1252-1263
NY Times. Ask Well. “Ask Well: Does Boiling or Baking Vegetables Destroy Their Vitamins?”
Mayo Clinic. “Vitamin C”