Benefits of Vitamin C
Introduction
Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. Humans, unlike most animals, are unable to synthesize vitamin C endogenously, so it is an essential dietary component .
Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters; vitamin C is also involved in protein metabolism . Collagen is an essential component of connective tissue, which plays a vital role in wound healing. Vitamin C is also an important physiological antioxidant and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E) . Ongoing research is examining whether vitamin C, by limiting the damaging effects of free radicals through its antioxidant activity, might help prevent or delay the development of certain cancers, cardiovascular disease, and other diseases in which oxidative stress plays a causal role. In addition to its biosynthetic and antioxidant functions, vitamin C plays an important role in immune function and improves the absorption of nonheme iron , the form of iron present in plant-based foods. Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, widespread connective tissue weakness, and capillary fragility.
The intestinal absorption of vitamin C is regulated by at least one specific dose-dependent, active transporter . Cells accumulate vitamin C via a second specific transport protein. In vitro studies have found that oxidized vitamin C, or dehydroascorbic acid, enters cells via some facilitated glucose transporters and is then reduced internally to ascorbic acid. The physiologic importance of dehydroascorbic acid uptake and its contribution to overall vitamin C economy is unknown.
Oral vitamin C produces tissue and plasma concentrations that the body tightly controls. Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg/day. However, at doses above 1 g/day, absorption falls to less than 50% and absorbed, unmetabolized ascorbic acid is excreted in the urine [4]. Results from pharmacokinetic studies indicate that oral doses of 1.25 g/day ascorbic acid produce mean peak plasma vitamin C concentrations of 135 micromol/L, which are about two times higher than those produced by consuming 200–300 mg/day ascorbic acid from vitamin C-rich foods . Pharmacokinetic modeling predicts that even doses as high as 3 g ascorbic acid taken every 4 hours would produce peak plasma concentrations of only 220 micromol/L .
The total body content of vitamin C ranges from 300 mg (at near scurvy) to about 2 g . High levels of vitamin C (millimolar concentrations) are maintained in cells and tissues, and are highest in leukocytes (white blood cells), eyes, adrenal glands, pituitary gland, and brain. Relatively low levels of vitamin C (micromolar concentrations) are found in extracellular fluids, such as plasma, red blood cells, and saliva
Recommended Intakes
Intake recommendations for vitamin C and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine (IOM) of the National Academies (formerly National Academy of Sciences) . DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender , include:
Table 1 lists the current RDAs for vitamin C . The RDAs for vitamin C are based on its known physiological and antioxidant functions in white blood cells and are much higher than the amount required for protection from deficiency . For infants from birth to 12 months, the FNB established an AI for vitamin C that is equivalent to the mean intake of vitamin C in healthy, breastfed infants.
| Age | Male | Female | Pregnancy | Lactation |
|---|---|---|---|---|
| 0–6 months | 40 mg* | 40 mg* | ||
| 7–12 months | 50 mg* | 50 mg* | ||
| 1–3 years | 15 mg | 15 mg | ||
| 4–8 years | 25 mg | 25 mg | ||
| 9–13 years | 45 mg | 45 mg | ||
| 14–18 years | 75 mg | 65 mg | 80 mg | 115 mg |
| 19+ years | 90 mg | 75 mg | 85 mg | 120 mg |
Sources of Vitamin C
Food
Fruits and vegetables are the best sources of vitamin C (see Table 2) . Citrus fruits, tomatoes and tomato juice, and potatoes are major contributors of vitamin C to the American diet . Other good food sources include red and green peppers, kiwifruit, broccoli, strawberries, Brussels sprouts, and cantaloupe (see Table 2) . Although vitamin C is not naturally present in grains, it is added to some fortified breakfast cereals. The vitamin C content of food may be reduced by prolonged storage and by cooking because ascorbic acid is water soluble and is destroyed by heat . Steaming or microwaving may lessen cooking losses. Fortunately, many of the best food sources of vitamin C, such as fruits and vegetables, are usually consumed raw. Consuming five varied servings of fruits and vegetables a day can provide more than 200 mg of vitamin C.
| Food | Milligrams (mg) per serving | Percent (%) DV* |
|---|---|---|
| Red pepper, sweet, raw, ½ cup | 95 | 106 |
| Orange juice, ¾ cup | 93 | 103 |
| Orange, 1 medium | 70 | 78 |
| Grapefruit juice, ¾ cup | 70 | 78 |
| Kiwifruit, 1 medium | 64 | 71 |
| Green pepper, sweet, raw, ½ cup | 60 | 67 |
| Broccoli, cooked, ½ cup | 51 | 57 |
| Strawberries, fresh, sliced, ½ cup | 49 | 54 |
| Brussels sprouts, cooked, ½ cup | 48 | 53 |
| Grapefruit, ½ medium | 39 | 43 |
| Broccoli, raw, ½ cup | 39 | 43 |
| Tomato juice, ¾ cup | 33 | 37 |
| Cantaloupe, ½ cup | 29 | 32 |
| Cabbage, cooked, ½ cup | 28 | 31 |
| Cauliflower, raw, ½ cup | 26 | 29 |
| Potato, baked, 1 medium | 17 | 19 |
| Tomato, raw, 1 medium | 17 | 19 |
| Spinach, cooked, ½ cup | 9 | 10 |
| Green peas, frozen, cooked, ½ cup | 8 | 9 |
Vitamin C
Is a glass of OJ or vitamin C tablets your go-to when the sniffles come? Loading up on this vitamin was a practice spurred by Linus Pauling in the 1970s, a double Nobel laureate and self-proclaimed champion of vitamin C who promoted daily megadoses (the amount in 12 to 24 oranges) as a way to prevent colds and some chronic diseases.
Vitamin C, or ascorbic acid, is a water-soluble vitamin. This means that it dissolves in water and is delivered to the body’s tissues but is not well stored, so it must be taken daily through food or supplements. Even before its discovery in 1932, nutrition experts recognized that something in citrus fruits could prevent scurvy, a disease that killed as many as two million sailors between 1500 and 1800. [1]
Vitamin C plays a role in controlling infections and healing wounds, and is a powerful antioxidant that can neutralize harmful free radicals. It is needed to make collagen, a fibrous protein in connective tissue that is weaved throughout various systems in the body: nervous, immune, bone, cartilage, blood, and others. The vitamin helps make several hormones and chemical messengers used in the brain and nerves. [2]
While megadosing on this vitamin is not uncommon, how much is an optimum amount needed to keep you healthy, and could taking too much be counterproductive?
Vitamins are substances that your body needs to grow and develop normally. Vitamin C is an antioxidant. It is important for your skin, bones, and connective tissue. It promotes healing and helps the body absorb iron.
Vitamin C comes from fruits and vegetables. Good sources include citrus, red and green peppers, tomatoes, broccoli, and greens. Some juices and cereals have added vitamin C.
Some people may need extra vitamin C:
- Pregnant/breastfeeding women
- Smokers
- People recovering from surgery
- Burn victims
No comments:
Post a Comment