Vitamin C: Everything You Need to Know

If you picture an orange when you think of vitamin C, you're right on -- the fruit, as well as other citrus fruits, is a vitamin C powerhouse. You may also quickly associate the vitamin with cold prevention, another understandable link, since some research -- and more products (and moms) -- tout it.

But vitamin C is a lot more than that, even though it doesn't get as nearly much attention as vitamin D, probably because far fewer Americans are deficient in it, says Dr. Gail Feinberg, chair of the primary care department at Touro University California College of Osteopathic Medicine. "Most people are getting a daily dose of vitamin C from their routine diets," she says.

[See: 7 Reasons to Choose a Plant-Based Diet.]

Still, it's important to appreciate the benefits of Vitamin C, because without it, we'd all have scurvy -- a now-rare disease in developed countries that can cause swollen, bleeding gums and other wounds. Here's what else you need know about this under-appreciated vitamin:

What is vitamin C?

Also known as L-ascorbic acid, vitamin C is a water-soluble vitamin, which means that if you take in more than your body needs, you pee it out. (Fat-soluble vitamins like A and D, on the other hand, are mostly stored in your fat tissues and liver, and are eliminated more slowly.) Because your body doesn't make vitamin C itself, you have to consume it, either in foods that naturally contain it or that are fortified with it, or with supplements, according to the National Institutes of Health Office of Dietary Supplements.

The health benefits of vitamin C

Here's where the research stands on vitamin C's various benefits:

-- Cold prevention. Interestingly, vitamin C's reputation as a cold-preventer or cold-shortener is a lot stronger than the research behind it. One 2013 review of 29 studies on the vitamin and colds found that "routine supplementation is not justified" to reduce the incidence of colds in the general population. "It has been shown to actually help with prevention of the common cold as well as shortening and treating this illness in some studies, and shown to be no help in others," Feinberg says.

-- Protection against free radicals. Vitamin C is a natural antioxidant, which means it helps protect against damage from free radicals, or molecules that can damage your cells. Your body is always generating free radicals, but certain experiences like smoking, sunbathing and even exercising can bring on more. That helps explain why the research does show vitamin C can be helpful for recovery from intense exercise. "Vitamin C is ... by nature anti-inflammatory because it blunts the effects of circulating free radicals," says Robin Foroutan, an integrative registered dietitian nutritionist in New York City and a spokesperson for the Academy of Nutrition and Dietetics.

-- Tissue health. Vitamin C is also key for skin and hair, bone and joint, and cardiovascular health because it's "an important cofactor in our own synthesis of collagen," Foroutan says. In other words, it helps your body process collagen, which is well-known to keep those tissues young. In the case of blood vessels, that means keeping them flexible and able to easily constrict and expand, Foroutan says.

-- Nutrient absorption. Vitamin C also partners with iron for optimal absorption, so if you're aiming to up your iron intake, consider consuming more vitamin C too -- perhaps some spinach alongside that steak?

-- Eye health. Your eyes contain high concentrations of vitamin C, which may help explain why some research has shown that people with vitamin C-rich diets may be less likely to get cataracts.

-- Weight control. Some research has linked vitamin C consumption with a lower body mass index and body fat percentage, although exactly why is unclear, Foroutan says.

-- Disease prevention. While some people believe vitamin C may help prevent conditions ranging from heart disease and cancer to depression and Alzheimer's disease, there's not enough research yet to support these claims, Feinberg says.

How much vitamin C should you have daily?

The recommended daily allowance of vitamin C is 90 milligrams for adult men and 75 milligrams for adult women. "Smokers need 35 milligrams more than that each day because of all the free radical damage they expose themselves to from cigarette smoke," Foroutan says. Folks who are exposed to a lot of secondhand smoke or UV rays may consider upping their dosage, too.

You can check your levels of vitamin C with a simple blood test from your doctor, Foroutan says. If you're seriously deficient, you'll feel it -- and feel the improvements quickly upon correcting the issue, Feinberg says. "In the U.S., deficiency occurs mostly in severely malnourished individuals, drug and alcohol abusers or those living in poverty or on diets that are void of fruits and vegetables," she says. "Early symptoms include weakness, irritability, weight loss and vague muscle and joint pain."

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Can you overdose on vitamin C?

Because vitamin C is water soluble, it's pretty hard to consume too much, experts say. Still, more isn't always better. For example, overdoing the vitamin C on a regular basis can lead to diarrhea and abdominal bloating, Feinstein says. Nausea, vomiting, cramps and other gastrointestinal issues can also occur. And some research has linked vitamin C intake with a certain type of kidney stone in men, so supplementation isn't usually recommended for men and others at risk for oxalate stones.

What foods are high in vitamin C?

Like all vitamins and minerals readily available in foods, consuming most, if not all, of your vitamin C in your diet is the best way to go since that's how your body was designed to process them. Most brightly-colored fruits and vegetables are rich in vitamin C -- think citrus fruits, bell peppers, broccoli, Brussels sprouts, tomatoes, papaya, kiwi, pineapple and cantaloupe. "It's good to rotate them," Foroutan says, "because each food has its own blend of not just vitamins and minerals, but also of phytonutrients and phytochemicals."

[See: 8 Foods Loaded With Vitamin C.]

Should I take a vitamin C supplement?

-- While most Americans are just fine without one, if you are at risk for or have been tested for a vitamin C deficiency, supplementation is a good idea. Even if you don't have or aren't at risk for a vitamin C deficiency, taking an over-the-counter supplement or multivitamin that contains 500 to 1000 milligrams daily won't hurt you, Feinberg says, "as long as you are not taking a combination pill with massive amounts of fat soluble vitamins ... which can cause toxicity."