Vitamin C: Health Benefits, Deficiency and Food Sources
Vitamin C (L-ascorbic acid) is a water soluble vitamin that most people readily associate with fresh fruits and vegetables. This vitamin is involved in the activity of several enzymes and works as a powerful antioxidant. Its multiple roles within the body include making collagen for connective fibers in tissues such as bones, teeth, skin and cartilage, making L-carnitine that is necessary for fat metabolism, helping to heal cuts and bruises, taking part in the formation of liver bile and production of adrenal hormones and neurotransmitters, enhancing absorption of non-heme iron, helping the blood vessels to relax and to keep them flexible, protecting the cells from oxidative stress, and promoting strong immune system and thus preventing infection.
Most experts agree that an adequate intake of vitamin C may help prevent immunodeficiency (e.g., when caused by enormous stress), cardiovascular disease, cataracts, prenatal health problems, bone loss and premature aging of the skin. Some of these benefits are largely due to the antioxidative properties of vitamin C. Recent research shows that vitamin C may also help reduce the risk of developing other medical conditions including asthma, age-related macular degeneration, periodontal disease and even cancer. In addition, vitamin C may be beneficial in treating allergies, eczema, sunburns, wounds, fighting certain viruses and lowering blood sugar levels in diabetics. Also, when taken together, vitamin C increases the potency of vitamin E.
Vitamin C is easily absorbed from the diet but it cannot be stored in the body and any excess amount is readily excreted through urine. Hence, overdose usually is not an issue. Five servings of fresh fruits and vegetables per day should for most people be sufficient to meet their daily recommended intake of this vitamin. Supplementation with vitamin C is often recommended to smokers, alcoholics, obese people and the elderly as well as to those who do not eat enough fresh fruits and vegetables. However, absorption is dose-dependent. Individuals who take a once-daily supplement of 500mg of vitamin C may not be able to absorb it all. In addition, some of the absorbed amount will not be metabolized and will be quickly flushed out from the body. Therefore, people are advised to take several smaller doses of supplements a day.
Deficiency of Vitamin C
Deficiency of vitamin C is rare in the developed world. However, certain populations may require increased intakes of this vitamin. For example, smokers need extra vitamin C because they have more free radicals in their bodies than non-smokers while people who regularly consume alcohol require more vitamin C because alcohol depletes this vitamin in body tissues. Other populations that may need to supplement their diet with vitamin C include the elderly, patients with impaired absorption of nutrients, severely obese individuals, people with compromised immune system, individuals who take steroids and those who do not eat enough fresh fruits and vegetables.
A lack of vitamin C in the diet causes impaired collagen synthesis. This results in symptoms such as sensitive inflamed gums (gingivitis), gum bleeding, loose tooth, dry and scaly skin, dry splitting hair, easy bruising and slow wound healing, nosebleeds, fluid retention, frequent infections, anemia and weakness. Severe long term deficiency of vitamin C can eventually lead to scurvy.
Overdose on Vitamin C
Excess vitamin C is not retained and so it does not build up in the body. Therefore, overdosing on vitamin C from a regular diet is practically impossible. However, exceeding the recommended dietary allowances (see the table below) through megadoses of dietary supplements may cause certain adverse reactions. These may include heartburn, upset stomach, nausea, vomiting, abdominal bloating and diarrhea. Chronic overdose may also cause headaches, sleeplessness and may promote build-up of kidney stones. In addition, increased intake of vitamin C may impair the effectiveness of the blood thinning agent warfarin.
Recommended Intake Levels of Vitamin C
Recommended dietary allowances (RDAs) and tolerable upper intake levels (ULs) for vitamin C are as follows (please note that smokers require additional 35mg/day):
|RDA (mg per day)||Upper Limit (mg per day)|
|Birth to 6 months||40 (*)||40 (*)||None established||None e.|
|7 – 12 months||50 (*)||50 (*)||None established||None e.|
|1 – 3 years||15||15||400||400|
|4 – 8 years||25||25||650||650|
|9 – 13 years||45||45||1,200||1,200|
|14 -18 years||75||65, pregnant 80, lactating 115||1,800||1,800|
|19 and older||90||75, pregnant 85, lactating 120||2,000||2,000|
* Adequate intake (AI) as no RDA has been established
Dietary Sources of Vitamin C
The chief dietary source of vitamin C are fresh fruits and vegetables. Foods and beverages fortified with vitamin C are also commonly available. Most fruits and vegetables contain some vitamin C. Those that are particularly high in this vitamin include Barbados cherry (1,678mg/gram), sea buckthorn berries (up to 1,550mg/100gram), guavas (228mg/100gram), blackcurrants (160mg/100gram), red peppers (128mg/gram), kale (120mg/100gram), kiwifruit (93mg/100gram), broccoli (89mg/100gram), Brussels sprouts (85mg/100gram), green peppers (80mg/100gram), papaya (61mg/100gram), strawberries (59mg/100gram), oranges (53mg/100gram), cauliflower (48mg/100gram), pineapple (48mg/100gram) and green peas (40mg/100gram).
Vitamin C is the least thermally and chemically stable of all vitamins. Prolonged storage (oxygen), light and, particularly, heat diminish vitamin C content of all foods. Since vegetables such as kale, broccoli, Brussels sprouts or cauliflower are usually not eaten raw, their vitamin C content is greatly reduced when steamed or cooked.
Vitamin C is probably the most popular stand-alone dietary supplement though it can also be found in most multivitamin and multimineral supplements. As it was mentioned above, it is poorly absorbed at high intakes and only partially metabolized and should better be taken in several smaller doses (e.g., 100mg) throughout the day.