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VITAMIN C (ASCORBIC ACID)

Vitamin C is also known as ascorbic acid. Vitamin C deficiency causes scurvy. As early as 3000 BCE, a scurvy epidemic was recorded in Egypt. In 1753, James Lind demonstrated experimentally that fruit consumption could alleviate scurvy in sailors during a long sea voyage. In 1854, the English court enacted laws stipulating that all sailors during long sea voyages be given a daily portion of fruits. In 1928, Albert Szent-Györgyi isolated a six-member carbon compound from the adrenal gland, oranges, and cabbage. In 1932, his research group demonstrated that this water-soluble substance could cure scurvy, and they named it ascorbic acid. Szent-Györgyi was awarded the 1937 Nobel Prize in Physiology or Medicine for his contributions.

Some mammals—such as monkeys, cows, sheep, and dogs—can produce vitamin C in the body. They do not have to rely on foods for vitamin C. Humans cannot produce vitamin C because we do not have an enzyme in the liver required for the de novo synthesis of vitamin C; thus, we need to acquire it from plant-based foods.

Vitamin C is an electron donor, a chemical entity that donates electrons to another chemical entity. All functions of vitamin C in the body are related to this electron donor property. Vitamin C can donate electrons to at least 12 different enzymes that are responsible for many physiological functions. One of these enzymes is involved in the synthesis of collagen. Collagens are the major proteins in the skin, cartilage, tendons, ligaments, and blood vessels.

Vitamin C can also donate electrons to free radicals. After accepting electrons from vitamin C, free radicals are neutralized and can no longer harm the cell. Vitamin C protects DNA, proteins, and lipids in the cell from free radical–induced oxidative damage. Vitamin C participates in many other physiological functions, including accelerating wound healing, repairing and maintaining healthy bones and teeth, and enhancing iron absorption in the intestines.

What Are the Symptoms of Vitamin C Deficiency?

 • Scurvy. Severe vitamin C deficiency causes scurvy, characterized by subcutaneous bleeding, hair and tooth loss, swollen joints, impaired wound healing, and even death. Nowadays, scurvy is a rare disease restricted only to a high-risk group that includes cancer patients with cachexia, a wasting syndrome in which patients lose weight and experience a decline in overall health and malnutrition. Alcoholics, drug abusers, and institutionalized elderly people are also especially vulnerable.

 • Vitamin C insufficiency. Vitamin C insufficiency implies the blood level of vitamin C is insufficient, although it has not reached the deficient state. The symptoms of vitamin C insufficiency include dry and cracked hair, periodontal disease, easy bruising, nosebleed, and bacterial infections.

Prevention and Treatment of Diseases

 • Prevention. Meta-analysis confirms that vitamin C can prevent breast cancer (47), renal cell cancer (100), bladder cancer (44), stomach cancer (107), cervical cancer (50), esophageal cancer (64), endometrial cancer (63), Alzheimer’s disease (37), gout (71), stroke (108), cervical intraepithelial neoplasia (51), cataracts (49), exercise-induced bronchoconstriction (65), atrial fibrillation (40), and sleep apnea (106).

 • Treatment. Meta-analysis confirms that vitamin C can treat breast cancer (47), hypertension (78), cardiovascular disease (48), asthma (38), hemodialysis (75), sleep apnea (106), and hypercholesterolemia (77).

Can Vitamin C Prevent or Treat the Common Cold?

Can vitamin C prevent you from catching a cold? This is still an unsettled question, taking a vitamin C supplement seems to prevent athletes from catching a cold, but it will not protect nonathletes. However, taking a vitamin C supplement soon after catching a cold may alleviate cold symptoms and accelerate the recovery. The recommended daily dose is 1,000 mg of vitamin C.

Which Food Items Are Vitamin C Rich?

Plant-based foods, such as fruits and vegetables, are excellent sources of vitamin C. Fruits—including oranges, grapefruits, lemons, limes, papayas, strawberries, pineapples, cantaloupes, and raspberries—are rich in vitamin C. Vegetables—such as broccoli, kale, potatoes, sweet potatoes, tomatoes, bell peppers, and cauliflower—contain high amounts of vitamin C.

This list of vitamin C–rich food items is adapted from information provided by the USDA.

Daily reference value of vitamin C is 60 mg according to the 2013 FDA food-labeling guidelines.

What Are the Recommended Dietary Allowances for Vitamin C?

The upper daily intake limit of vitamin C is 2,000 mg.

Vitamin C Supplements

 • Dosage. The most common dosages of vitamin C supplements are 50–1,000 mg. Vitamin C supplementation has beneficial effects on health, but high-dose vitamin C supplements can cause diarrhea and other digestive problems. Avoid taking more than 2,000 mg of vitamin C per day.

 • Types. Various vitamin C supplements are available in the marketplace. Although there are many different kinds, they are all similar in regard to bioavailability. There is no evidence that one product is better than the other in terms of their absorption or efficacy. Ascorbic acid and sodium ascorbate are the two most common vitamin C supplements. Vitamin C palmitate converts to vitamin C and palmitate in the intestines. Some manufacturers claim that their products contain a 100% “reduced form” of vitamin C. The fact is that all vitamin C supplements contain only the “reduced form” if manufactured properly.

 • Liposomal vitamin C. Liposomal vitamin C is a lipid formulation in which water-soluble vitamin C is encapsulated in liposomes made of phospholipids. The logic behind the design was that the encapsulation of vitamin C in a liposomal form could enhance its absorption in the intestines, thereby elevating the blood level of vitamin C. However, the clinical data so far do not seem to support such claims. If you need to take a vitamin C supplement, choose ascorbic or sodium ascorbate. You do not need to purchase expensive products like liposomal vitamin C.

 • Cataracts. Vitamin C may prevent cataracts and mitigate the condition. Studies from England have shown that taking a vitamin C supplement at a dose of 250 mg daily for 10 years curtailed the risk of cataracts.

 • Smoking. Cigarette smoke can deplete vitamin C in the lungs as well as the rest of the body, causing insufficient vitamin C and free radical–mediated oxidative stress. It is imperative that smokers take vitamin C supplementation to avoid vitamin C insufficiency and its deleterious consequences.

 • Hypertension. Vitamin C supplementation can lower blood pressure, and this beneficial effect is more robust in hypertensive patients. Vitamin C reduces blood pressure through inhibition of endothelin-1, a vasoactive protein that elevates blood pressure.

 • Gout. Vitamin C supplements may alleviate gout symptoms. The suggested daily dose is 500 mg of vitamin C.

 • Premature mortality. Vitamin C may decrease the risk of premature death and increase life expectancy. Studies from the US have shown that vitamin C supplementation or sufficient dietary intake of vitamin C could prolong one’s life-span. The suggested daily dose is 500 mg of vitamin C.

 • Preeclampsia. Vitamin C taken together with vitamin E can lower the risk of preeclampsia in pregnant women. Symptoms of preeclampsia include hypertension, edema, and renal problems. The suggested daily doses are 500 mg of vitamin C and 100 IU of vitamin E.

 • Bruises. Vitamin C supplements can help prevent bruising. The suggested daily dose is 500 mg of vitamin C.

 • Cancers. High-dose intravenous vitamin C therapy is effective in treating certain types of cancers, particularly in terminally ill cancer patients who have refused any further chemotherapy. (See chapter 47, “Breast Cancer,” for details.)

Safety Issues

 • Side effects. High-dose vitamin C supplementation may increase the risk of cataracts and kidney stones. Vitamin C can be converted to oxalate, which forms oxalate crystals, leading to kidney stones. Studies from Switzerland have shown that taking a vitamin C supplement at a daily dose of 1,000 mg increases one’s risk of kidney stones by 66%. Another study from Sweden shows that taking a vitamin C supplement at a dose of 1,000 mg for 10 years increases the risk of cataracts by 25%.

 • Iron. Vitamin C boosts the absorption of iron by the intestines. People who take iron supplements together with vitamin C supplements need to monitor their blood iron levels to avoid problems associated with iron overload.

What Types of Drugs May Interact with Vitamin C?

 • Oral contraceptives and aspirin. Both oral contraceptives and aspirin can reduce the blood level of vitamin C.

 • Acetaminophen (Tylenol). Vitamin C increases the blood level of acetaminophen and exacerbates acetaminophen-induced liver damage. People who take vitamin C supplements together with acetaminophen need to be aware of the potential problems associated with liver damage.

 • Anticoagulants. Vitamin C decreases the efficacy of anticoagulant drugs such as warfarin and heparin.