Vitamin C: benefits, research and safety

What vitamin C is

Vitamin C, also called ascorbic acid, is a water-soluble vitamin. Most animals make their own, but humans lost that ability long ago, along with other primates and guinea pigs. That means every bit of vitamin C you have comes from food or supplements.

Because it dissolves in water, your body does not store much of it. Extra amounts leave in urine, which is why a steady daily intake matters more than an occasional large dose. When intake stays very low for weeks, the result is scurvy, the disease that once plagued sailors on long voyages. In 1747 a Scottish naval surgeon, James Lind, showed that oranges and lemons helped sailors recover from scurvy, one of the earliest controlled experiments in medicine. Scurvy is rare in the US today, though it still turns up in people with very limited diets.

What vitamin C does in the body

Vitamin C has several jobs, and some of them matter directly for your heart and circulation.

• It is needed to make collagen, the protein that gives structure to skin, gums, tendons and the walls of your blood vessels. Easy bruising and bleeding gums are early signs of scurvy for this reason.
• It is an antioxidant. It neutralizes free radicals, unstable molecules that can damage cells, fats and DNA when they build up.
• It helps recycle vitamin E, another antioxidant, back to its active form so it can keep protecting cell membranes.
• It improves absorption of non-heme iron, the type found in beans, lentils, spinach and fortified cereals.
• It helps the body make carnitine, which carries fats into cells to be burned for energy, and some brain chemicals such as norepinephrine.

It also supports normal immune function. White blood cells hold high concentrations of vitamin C and use it up quickly during an infection.

What vitamin C has been studied for

Heart and blood vessel health

Researchers have been interested in vitamin C and the heart for a long time. Oxidized LDL cholesterol is one of the things that helps plaque form in artery walls, and vitamin C is an antioxidant, so the idea makes sense. Large observational studies have found that people who eat plenty of fruit and vegetables and have higher blood levels of vitamin C tend to have lower rates of heart disease.

Trials that gave people vitamin C supplements have had mixed results. Several large studies did not find that extra vitamin C reduced heart attacks or strokes in people who were already reasonably well nourished. The NIH Office of Dietary Supplements sums up the evidence as inconclusive, which is why the usual advice is to get vitamin C from food first and to view supplements as a way of filling gaps.

Blood vessel function and blood pressure

Some smaller studies have looked at how vitamin C affects the lining of blood vessels (the endothelium) and how well arteries relax. Others have measured blood pressure. Several found modest benefits, though results vary from study to study, and scientists are still working out who responds best.

Cholesterol and blood sugar

A number of trials have measured cholesterol, triglycerides and blood sugar in people taking vitamin C, including adults with type 2 diabetes. Some reported small improvements and others found none. Smokers and people with low starting levels seem more likely to see a change, which fits with the idea that vitamin C helps most when you are short on it.

Colds

For the general population, taking vitamin C every day does not seem to reduce how often people catch a cold. Regular supplements may shorten colds slightly, and people under heavy physical stress, such as marathon runners, may benefit more.

How much vitamin C you need

The Recommended Dietary Allowance (RDA) for adults is the amount that meets the needs of nearly all healthy people. Smokers need more because smoking uses up vitamin C faster.

The Daily Value on US food and supplement labels is 90 mg. Most Americans get close to the RDA from food, but people who smoke, people with very limited diets and some people with digestive conditions that affect absorption are more likely to fall short.

Best food sources of vitamin C

Fruits and vegetables supply almost all the vitamin C in the American diet. A single serving of several of these foods covers most or all of a day's needs.

Vitamin C breaks down with heat, light and long storage, so fresh and lightly cooked produce keeps more of it. Steaming or microwaving vegetables loses less than boiling them in a big pot of water. Eating some foods raw, such as peppers, berries and citrus, is an easy way to get the full amount.

Amounts used in studies and supplement forms

Research on heart and metabolic health has often used 500 to 1,000 mg of vitamin C a day, well above the RDA but under the 2,000 mg upper limit. Studies usually run for several weeks to several months.

Most supplements use ascorbic acid, which the body absorbs about as well as the vitamin C in food. Mineral ascorbates such as sodium ascorbate and calcium ascorbate are less acidic and may be gentler on the stomach for some people. Absorption becomes less efficient as the dose climbs, so a moderate amount taken regularly makes more sense than an occasional megadose.

Safety and who should talk to a doctor

Vitamin C has very low toxicity, and food sources are safe for everyone. With supplements, the most common problems above the 2,000 mg upper limit are diarrhea, nausea and stomach cramps. A few groups should be more careful:

• People with hemochromatosis, a condition that causes iron overload, should talk to their doctor, because vitamin C increases iron absorption.
• People with a history of kidney stones should ask before taking high doses, since large amounts may raise the risk of stones in some people.
• If you are having chemotherapy or radiation treatment, check with your cancer care team before taking antioxidant supplements.
• People taking a statin together with niacin for cholesterol should mention any antioxidant supplements to their doctor, as the combination has been studied for possible interactions.

During pregnancy and breastfeeding, vitamin C needs go up slightly, and a prenatal vitamin plus a diet with plenty of fruit and vegetables usually covers them. If you take prescription medicine, it is always a good idea to share your supplement list with your doctor or pharmacist.

Why vitamin C is in ColestZen

ColestZen is designed to support heart and metabolic health, and vitamin C fits that aim well. It is needed for the collagen in blood vessel walls, it protects cells from oxidative stress and it helps recycle vitamin E, which is also part of the ColestZen formula. Those two antioxidants have long been studied together, and they work as a pair in the body.

The brand does not publish how much vitamin C each capsule contains, so we cannot say how the amount compares to the RDA or to research doses. What we can say is that vitamin C is one of the safest and best understood nutrients, and it makes sense in a blend that also includes cinnamon bark, alpha lipoic acid and other ingredients studied for blood sugar and cholesterol support. For the full picture on the formula, its price and the 60-day money-back guarantee, read our full ColestZen review.

Whatever supplement you choose, a plate that is half fruit and vegetables gives you vitamin C along with fiber and potassium, which also support a healthy heart.

Frequently asked questions

Sources

• NIH Office of Dietary Supplements: Vitamin C fact sheet for health professionals
• Food and Nutrition Board, National Academies: Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (2000)
• MedlinePlus: Vitamin C