Vitamin C [Ascorbic acid]
- overview
University of Maryland Medical Center
Overview
Vitamin C is a water-soluble vitamin needed for the growth and repair of tissues in all parts of the body. It is necessary to form collagen, an important protein used to make skin, scar tissue, tendons, ligaments, and blood vessels. Vitamin C is essential for the healing of wounds, and for the repair and maintenance of cartilage, bones, and teeth.
Vitamin C is one of many antioxidants. Vitamin E and beta-carotene are two other well known antioxidants. Antioxidants are nutrients that block some of the damage caused by free radicals, which are by-products that result when our bodies transform food into energy. The build up of these by-products over time is largely responsible for the aging process and can contribute to the development of various health conditions such as cancer, heart disease, and a host of inflammatory conditions like arthritis. Antioxidants also help reduce the damage to the body caused by toxic chemicals and pollutants such as cigarette smoke.
Vitamin C deficiency can lead to dry and splitting hair; gingivitis (inflammation of the gums) and bleeding gums; rough, dry, scaly skin; decreased wound-healing rate, easy bruising; nosebleeds; weakened enamel of the teeth; swollen and painful joints; anemia; decreased ability to ward off infection; and, possibly, weight gain because of slowed metabolic rate and energy expenditure. A severe form of vitamin C deficiency is known as scurvy, which mainly affects older, malnourished adults.
The body does not manufacture vitamin C on its own, nor does it store it. It is therefore important to include plenty of vitamin C-containing foods in one's daily diet. Large amounts of vitamin C are used by the body during any kind of healing process, whether it's from an infection, disease, injury, or surgery. In these cases extra vitamin C may be needed.
Uses
Low levels of vitamin C have been associated with a variety of conditions including hypertension, gallbladder disease, stroke, some cancers, and atherosclerosis (the build up of plaque in blood vessels that can lead to heart attack and stroke; conditions that are caused by atherosclerotic build up are often collectively referred to as cardiovascular diseases). Eating adequate amounts of vitamin C in the diet (primarily through lots of fresh fruits and vegetables) may help reduce the risk of developing some of these conditions. There is little evidence, however, that vitamin C supplements can cure any of these diseases.
As an anti-oxidant, vitamin C plays an important role in protecting against the following:
Heart Disease
Results of scientific studies regarding the benefit of vitamin C for heart disease or stroke is somewhat confusing. While not all of the studies agree, some information suggests that vitamin C may help protect blood vessels from the damaging effects that lead to or result from the presence of atherosclerosis.
For example, those with low levels of vitamin C may be more likely to have a heart attack, stroke, or peripheral artery disease, all potential outcomes of atherosclerosis. Peripheral artery disease is the term used to describe atherosclerosis of the blood vessels to the legs. This can lead to pain with walking, known as intermittent claudication.
In terms of damage that can cause atherosclerosis, some studies have shown that vitamin C helps prevent oxidation of LDL (bad) cholesterol – a process that contributes to plaque buildup in the arteries.
Under most circumstances, dietary vitamin C is adequate for protecting against the development of or consequences from cardiovascular disease. If you have low levels of this nutrient, however, and find it difficult to obtain through dietary sources, a knowledgeable healthcare provider may recommend vitamin C supplements.
High Cholesterol
Information from several studies, involving only small numbers of people, suggest that vitamin C (3 glasses of orange juice per day or up to 2000 mg per day as a supplement) may help decrease total and LDL cholesterol and triglycerides, as well as increase HDL levels (the good kind of cholesterol). Studies evaluating larger groups of people would be helpful in determining how accurate these preliminary research results are and to whom this potential benefit applies.
High Blood Pressure
Free radicals, the damaging by-products of metabolism mentioned earlier, are associated with higher blood pressure in studies of animals and people. Population based studies (which involve observing large groups of people over time) suggest that people who eat foods rich in antioxidants, including vitamin C, are less prone to high blood pressure than people without these nutritious foods in their diet. For this reason, many clinicians recommend foods rich in vitamin C, particularly if you are at risk for high blood pressure. In fact, the diet most frequently recommended for treatment and prevention of hypertension, known as the DASH (Dietary Approaches to Stop Hypertension) diet advocates lots of fruits and vegetables, which are loaded with antioxidants.
Common Cold
Despite the popular belief that vitamin C can cure the common cold, the scientific evidence supporting this conviction is limited. There have been a few studies suggesting that taking large doses of vitamin C supplements at the onset of cold or flu symptoms, or just after exposure to one of these viruses, can shorten the duration of the cold or ward it off altogether. However, the majority of studies, when looked at collectively, lead researchers to conclude that vitamin C does not prevent or treat the common cold. Some experts suggest that vitamin C may only be useful in case of a cold if you have low levels of this nutrient to begin with. Another possibility is that the likelihood of success may be very individual – some improve, while others do not. If you are amongst the 67% of people who believe that vitamin C is helpful for your colds, there may be power in your conviction. In other words, your experience is probably more important than what the research is stating. Talk to your doctor about any pros and cons with regards to using vitamin C during cold and flu season.
Cancer
While the precise role of vitamin C in preventing cancer remains controversial, results of many population based studies (evaluating groups of people over time) imply that foods rich in vitamin C may be associated with lower rates of cancer, including skin cancer, cervical dysplasia (changes to the cervix which may be cancerous or precancerous, picked up by pap smear), and, possibly, breast cancer. At best, however, particularly for breast cancer, the specific connection of vitamin C and cancer prevention is weak. This is mainly because protection comes from eating foods, such as fruits and vegetables, which contain many beneficial nutrients and antioxidants, not only vitamin C.
Also, there is no evidence that taking large doses of vitamin C once diagnosed with cancer will help your treatment. In fact, there is concern that large doses of antioxidants from supplements could interfere with chemotherapy medications. Much more research in the area of antioxidants and cancer treatment is needed.
Osteoarthritis
Vitamin C is essential for normal cartilage. Plus, free radicals can be produced in the joints and have been implicated in many degenerative changes in the aging body, including destruction of cartilage and connective tissue that lead to arthritis. Antioxidants appear to offset the damage caused by free radicals. Although further evidence is needed to substantiate these claims, studies of groups of people observed over time suggest that vitamin C, as well as vitamin E, may help to reduce the symptoms of OA.
Obesity and Weight Loss
Studies suggest that obese individuals may have lower vitamin C levels than nonobese individuals. Researchers speculate that insufficient amounts of vitamin C may contribute to weight gain by decreasing metabolic rates and energy expenditures. Many sensible weight loss programs will be sure to include foods rich in vitamin C, such as plenty of fruits and vegetables.
Cataracts
Studies have shown that vitamin C may slow or even stop the progression of cataracts in the elderly. A recent study, for example, of women from the Nurses' Health Study (a very large, important study that has followed women over many years) showed that women under 60 years of age who had high dietary intake of vitamin C or who had used vitamin C supplements for 10 years or more had significantly reduced chances of developing cataracts.
Age-related Macular Degeneration
Vitamin C works together with other antioxidants like selenium, beta-carotene, and vitamin E to protect the eyes against developing macular degeneration. This is a painless, degenerative eye disease that affects more than 10 million Americans. It is the leading cause of legal blindness in persons over the age of 55 in the United States. While complete blindness does not occur in most people with the disorder, macular degeneration often interferes with reading, driving, or performing other daily activities.
While not all research agrees, antioxidants, including vitamin C, primarily from dietary sources may help prevent macular degeneration. Many qualified clinicians will recommend a combination of these nutrients for treating or preventing this serious and frustrating eye disorder.
Diabetes
Vitamin C may be helpful for people with diabetes in a number of ways. First, some studies suggest that people with diabetes have high levels of free radicals (the damaging metabolic by-products, mentioned earlier, associated with many chronic illnesses) and low levels of antioxidants, including vitamin C. This imbalance may contribute to the fact that those with diabetes are at greater risk for developing conditions such as high cholesterol and atherosclerosis.
Secondly, insulin (which is low in type 1 diabetics and does not function properly in type 2 diabetics) helps cells in the body take up the vitamin C that they need to function properly. At the same time, lots of circulating blood sugar (glucose), as is often the present in diabetics, prevents the cells from getting the vitamin C that they need, even if eating lots of fruits of vegetables. For this reason, taking extra vitamin C in the form of supplements may be helpful in those with diabetes.
Alzheimer's Disease and other types of Dementia
While the evidence is somewhat stronger for another important antioxidant, namely vitamin E, vitamin C may help prevent the development of Alzheimer's disease. It may also improve cognitive function in dementia from causes other than Alzheimer's (such as multiple strokes). The use of these antioxidants for improving cognitive ability in those who already have dementia of the Alzheimer's type has not been well tested to date.
Other
Although the information is somewhat limited, studies suggest that vitamin C may also be helpful for:
- Boosting immune system function
- Maintaining healthy gums
- Relieving eye pressure in those with glaucoma
- Improving visual clarity for those with uveitis (an inflammation of the middle part of the eye)
- Slowing progression of Parkinson's disease
- Treating allergy-related conditions, such as asthma, eczema, and hay fever (called allergic rhinitis)
- Relieving pain from pancreatitis; vitamin C levels are often low with this condition
- Reducing effects of sun exposure, such as sunburn or redness (called erythema) and even, possibly, skin cancer
- Alleviating dry mouth, particularly from antidepresant medications (a common side effect from these drugs)
- Healing burns and wounds
Dietary Sources
Since vitamin C is not produced by the body, it must be obtained from fruits and vegetables. Some excellent sources of vitamin C are oranges, green peppers, watermelon, papaya, grapefruit, cantaloupe, strawberries, kiwi, mango, broccoli, tomatoes, brussels sprouts, cauliflower, cabbage, and citrus juices or juices fortified with Vitamin C. Raw and cooked leafy greens (turnip greens, spinach), red and green peppers, canned and fresh tomatoes, potatoes, winter squash, raspberries, blueberries, cranberries and pineapple are also rich sources of Vitamin C. Vitamin C is sensitive to light, air, and heat, so it is best to eat fruits and vegetables raw, or minimally cooked in order to retain their full vitamin C content.
