FOODS HIGH IN ASCORBIC ACID (VITAMIN C)
|6 or 7 Brussels sprouts
||87 milligrams vitamin C
|1 cup cauliflower
||62 milligrams vitamin C
|1 medium orange or 1/2 cup orange juice
||60 milligrams vitamin C
|1 cup shredded cabbage
||47 milligrams vitamin C
|1 slice watermelon
||42 milligrams vitamin C
|1/2 grapefruit or 2/3 cup grapefruit juice
||40 milligrams vitamin C
|1 medium potato
||30 milligrams vitamin C
Ascorbic acid, also called vitamin C, helps bind cells together and promotes healing. It is found in certain fruits and vegetables (see box above), and a well-balanced diet with a variety of healthful foods should supply all the vitamin C that you need. The recommended dietary allowance (RDA) for older adults is 60 milligrams (mg) per day. The optimal intake of vitamin C is approximately 300-400 mg per day. A single 8-ounce glass of orange juice contains about 100 mg of vitamin C.
Vitamin C deficiency, known as scurvy, is rare. It is seen occasionally in people whose diets do not supply enough vitamin C - some older adults who live alone, alcoholics and drug abusers, for example. Symptoms of scurvy include anemia, loose teeth, red and swollen gums, wounds that do not heal and small broken blood vessels that cause tiny purplish-red spots in the skin. Scurvy is easily prevented and is treated by increasing the intake of vitamin C through diet and a supplement.
Getting the right amount of vitamin C
You should take a vitamin C supplement only if your diet does not supply enough to prevent and treat a vitamin C deficiency, or if your body has a special demand for more vitamin C due to surgery, smoking or an infectious disease. Although doses that far exceed the RDA are touted as remedies for many conditions — from the common cold to cancer — research does not support such claims. There is no convincing evidence that taking supplements of vitamin C prevents any disease.
If you use a vitamin C supplement without a doctor’s supervision, do not take more than the RDA. Higher doses have few beneficial effects except in people with scurvy, and high-dose products are more expensive. Also, taking high doses of vitamin C is risky for people with a history of kidney stones and for people who use anticoagulants (drugs that prevent blood clots from forming in the blood vessels) such as warfarin (COUMADIN). If you are taking high doses of vitamin C and want to stop, do not stop suddenly. Reduce your dose gradually because your body needs time to adjust to the reduction.
Vitamin C and your health
One of the most common uses for large doses of vitamin C has been to prevent or lessen the severity of colds. A recent study randomized people to receive a supplement containing either 30 mg of vitamin C (less than one-half of the recommended daily allowance) or 1 gram or 3 grams of vitamin C upon the onset of a cold and for two days subsequently. There was no difference in the duration or severity of colds in people getting 1 or 3 grams of vitamin C and those getting only 30 mg a day.
A 2004 review of short-term, randomized controlled trials published by the Cochrane Collaboration, a highly respected nonprofit organization, found that taking vitamin C does not prevent upper respiratory infections such as the common cold.
A meta-analysis of three small trials in older adults published in the Aug. 28, 1999, issue of British Medical Journal found no beneficial effect of vitamin C on decreasing mortality.
The Medical Letter editors caution that high doses of vitamin C — more than 1,000 mg — are poorly absorbed, cause diarrhea and could increase the risk of kidney stones in people prone to developing them.
A study published in February 2013 in the Journal of the American Medical Association showed that the use of high-dose ascorbic acid supplements (approximately 1,000 mg) in men had an increased risk of kidney stones. The authors of the article stated, “Currently there are no well-documented benefits of high-dose ascorbic acid supplement use and, therefore, it seems prudent to advise that high-dose preparations be avoided, particularly by those with a history of kidney stones.”
A large study published in the January 2009 issue of the Journal of the American Medical Association refutes the belief that vitamins, specifically large quantities of vitamins C and E, can prevent cancer. The study’s authors concluded, "These data provide no support for the use of these supplements in the prevention of cancer in middle-aged and older men."
Vitamin C could be recommended as a cancer preventive only if it reduced the number of cases of cancer in a randomized controlled trial. In fact, for almost a decade, there has been such a study under way in China in which patients with precancerous lesions in their stomachs were randomized to receive either a combination of drugs, vitamins (C and E) plus a micronutrient (selenium), or garlic. The trial found that neither garlic nor the combination of vitamins and a micronutrient had any effect on reducing the occurrence of gastric cancer.
A large study sought to examine the use of vitamins C and E in ways that had not previously been studied. The authors of the study, which was recently published in the Archives of Ophthalmology, stated, “There have been no data for vitamin E treatment durations longer than 6.5 years in men and no data for supplementation with vitamin C alone in men or women.” Previous longer-term studies in women had failed to show any benefit of vitamin E for cataract prevention.
The authors’ conclusion adds cataracts to the list of diseases not prevented by vitamins C or E: “Long-term alternate-day use of 400 IU of vitamin E and daily use of 500 mg of vitamin C had no notable beneficial or harmful effect on the risk of cataracts.”
A recent Journal of Parenteral and Enteral Nutrition (JPEN) systematic review revealed that, with a few possible exceptions, dietary supplements offer no benefits to well-nourished adults eating a Western diet and, in many cases, may be harmful. The results of this study reinforce our longstanding view that there is little evidence that dietary supplements are either safe or effective.
The study authors concluded that with the possible exception of vitamin D in elderly patients and omega-3 fatty acids in patients with a history of cardiovascular disease, no data support the widespread use of dietary supplements in the U.S. and other Western countries. Indeed, the data suggest that certain commonly used dietary supplements, including beta-carotene, vitamin A, and vitamin E, may be harmful. We agree.
In 2020, JAMA Network Open published results of a randomized clinical trial showing that vitamin C supplements, alone or in combination with zinc supplements, were not effective for treating COVID-19 but did cause gastrointestinal adverse effects, including diarrhea, nausea, or stomach pain or cramps.