VITAMIN C: POWERFUL ANTIOXIDANT AND IMMUNE SUPPORTER

What is vitamin C?

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin found naturally in some foods, added to others, and available as a dietary supplement. Humans, unlike most animals, cannot synthesize vitamin C in their bodies, so it is an (essential) dietary component that must be taken from outside.

What are the dietary sources?

Fruits and vegetables are the best sources of vitamin C. Citrus fruits, tomatoes, tomato juice, and potatoes are the main foods that contribute vitamin C to the diet. Other good food sources include red and green peppers, kiwi, broccoli, strawberries, Brussels sprouts, and cantaloupe. Vitamin C is not naturally found in cereals but is added to some fortified breakfast cereals. The vitamin C content of foods can be reduced by prolonged storage and cooking because ascorbic acid is water-soluble and destroyed by heat. Steaming or microwaving can reduce losses. Fortunately, many of the best sources of vitamin C, such as fruits and vegetables, are usually consumed raw. Eating five servings of fruits and vegetables daily can provide more than 200 mg of vitamin C.

What is the recommended daily dose?

According to the US National Institutes of Health, the Recommended Daily Dietary Allowance (RDA) of vitamin C is 90 milligrams (mg) per day for men and 75 mg for women. Pregnant or breastfeeding women should consume up to 120 mg of vitamin C daily. Research also shows that smokers need 35 mg more vitamin C than non-smokers. Many researchers think we should consume significantly more vitamin C than the RDA. For example, the daily dose of vitamin C used in studies showing a reduced risk of cataracts was 500 mg. Long-term studies found that people who took more than 700 mg of vitamin C supplements per day had a 25 percent lower risk of coronary heart disease than people who did not take vitamin C supplements.

Vitamin C supplementation

When five fruits and vegetables rich in vitamin C are consumed daily, the recommended daily amount can be easily reached. However, when it cannot be taken at sufficient levels with food, the use of supplements containing vitamin C gains importance. These supplements are available on the market, mostly in ester or salt form, and in doses ranging up to 1000 mg. A 1000 mg supplement, formulated taking into account the absorption and metabolism of the vitamin, will provide our body with approximately 200 mg of active ascorbic acid, which is the optimum amount for supplementation. 

Recent research on the protective effect against COVID-19 and whether it is effective in treatment has led to a significant increase in the use of supplements containing vitamin C. There are different concentrations of vitamin C supplements on the market, and since these supplements can be purchased without a prescription, it is possible to take more than the amount we need when used unconsciously. The maximum daily limit for vitamin C is 2 grams (2000 mg). If this dose is exceeded, unwanted effects may occur. The most common undesirable effects are diarrhea, nausea, abdominal pain, and other digestive system problems. For people with a history of kidney stones, taking more than the daily limit of vitamin C is even more dangerous. In addition, vitamin C supplements interact with certain medications, such as amphetamine derivatives and deferoxamine, and should not be used inadvertently. Antioxidants, when used in high doses, can themselves be converted into metabolites that can lead to oxidation. For this reason, it should be remembered that vitamin C should be used in appropriate doses to protect health.

What are the benefits of vitamin C?

Vitamin C is essential in collagen synthesis, thus in the provision of normal connective tissue, wound healing, and the formation of bone tissue. It helps the absorption of iron. Increases the utilization of folic acid (vitamin B9). Vitamin C has been shown to replenish other antioxidants in the body, including vitamin E. It also plays an important role in the body's immune functions.

Because of its function as an antioxidant and its role in immune function, vitamin C is known as a tool to help prevent and/or treat numerous health conditions. These benefits include reduced risk of heart disease, reduced risk of some cancers, some anti-aging effects, protection against infections, strengthening of blood vessel walls, improved blood circulation, reduced blood cholesterol, and improved liver function. Let's take a brief look at some of the diseases or conditions in which vitamin C may play a role, such as cancer, cardiovascular disease, cataract, and the common cold.

Cancer prevention and treatment

Evidence from many studies suggests that consuming more fruits and vegetables, perhaps in part due to their high vitamin C content, is associated with a lower risk of most types of cancer. Vitamin C may limit the formation of carcinogens by regulating the immune response and, through its antioxidant function, possibly reduce the damage that can lead to cancer.

Many studies have found an inverse association between dietary vitamin C intake and cancers of the lung, breast, colon or rectum, stomach, oral cavity, larynx or pharynx, and esophagus. Vitamin C levels in the blood are also lower in people with cancer than in healthy people.

Some studies suggest that high doses of vitamin C have beneficial effects on quality of life and survival in patients with terminal cancer.

Cardiovascular disease

Evidence from many epidemiologic studies suggests that a high intake of fruits and vegetables is associated with a reduced risk of cardiovascular disease. This association may be partly attributable to the antioxidant content of these foods. In addition to its antioxidant properties, vitamin C has been shown to reduce monocyte adhesion to the endothelium, improve endothelium-dependent nitric oxide production and vasodilation, and reduce vascular smooth muscle cell apoptosis, which prevents plaque instability in atherosclerosis (thus improving vascular occlusion).

In the Nurses' Health Study, a 16-year prospective study involving 85,118 female nurses, vitamin C intake from both dietary and supplemental sources was inversely associated with coronary heart disease risk. However, dietary vitamin C alone did not show a significant association, suggesting that those who use vitamin C supplements may have a lower risk of coronary heart disease.

A study of 20,649 British adults found that those in the top quartile of baseline plasma vitamin C concentrations had a 42% lower risk of stroke than those in the bottom quartile. Nine studies involving 293,172 people without coronary heart disease at baseline found that those taking ≥700 mg/day of supplemental vitamin C had a 25% lower incidence of coronary heart disease than those not taking supplemental vitamin C.

Cataract

Higher dietary intake of vitamin C has been associated with a lower risk of cataract formation in some studies. In a 5-year study conducted in Japan, higher dietary vitamin C intake was associated with a reduced risk of cataract development in a group of more than 30,000 adults aged 45–64 years. Results from two case-control studies suggest that vitamin C intake of more than 300 mg/day reduces the risk of cataract formation by 70%–75%.

The common cold

In the 1970s, Linus Pauling suggested that vitamin C could successfully treat and/or prevent the common cold. Subsequent studies have shown that prophylactic use of vitamin C in the general population reduces the duration of the common cold by 8% in adults and 14% in children. However, in studies involving marathon runners, skiers, and soldiers exposed to extreme physical exercise and/or cold environments, prophylactic vitamin C use at doses ranging from 250 mg/day to 1 g/day reduced the incidence of colds by 50%. Studies also suggest that regular vitamin C intake at doses of at least 200 mg/day may be beneficial for the elderly and chronic smokers. The use of vitamin C supplements may shorten the duration of the common cold and improve symptom severity in the general population, possibly due to the antihistamine effect of high doses of vitamin C. Taking vitamin C after the onset of cold symptoms did not affect cold duration or symptom severity.

Vitamin C deficiency

Vitamin C deficiency causes scurvy. Although the time it takes for scurvy to develop depends on the vitamin C stores in the body, symptoms can appear within a month in cases where vitamin C intake is very low or absent (less than 10 mg/day). Initial symptoms may include fatigue, weakness, and inflammation of the gums. As vitamin C deficiency progresses, collagen synthesis is impaired and connective tissues weaken, causing joint pain and poor wound healing. Other symptoms of scurvy include depression as well as swollen, bleeding gums and loosening or loss of teeth due to tissue and capillary fragility. Iron deficiency anemia can also occur due to increased bleeding and decreased iron absorption due to low vitamin C intake. Bone disease may be present in children. Left untreated, scurvy is fatal.

Until the late 18th century, many sailors on long ocean voyages who took little or no vitamin C contracted or died from scurvy. In the mid-1700s, British Navy surgeon Sir James Lind conducted experiments and found that consuming citrus fruits or fruit juices could treat scurvy, but it was not until 1932 that scientists were able to prove that ascorbic acid was the active ingredient.

Today, vitamin C deficiency and scurvy are rare in developed countries. Clear signs of deficiency only occur if vitamin C intake falls below about 10 mg per day for weeks. Vitamin C deficiency is rare in developed countries but can still occur in people with a limited variety of foods.

Groups at high risk of vitamin C deficiency

Smokers and passive smokers

Studies consistently show that smokers have lower plasma and leukocyte vitamin C levels than non-smokers, partly due to increased oxidative stress. Therefore, smokers require 35 mg more vitamin C per day than non-smokers. Exposure to secondhand smoke also lowers vitamin C levels. Although research has not established a specific vitamin C requirement for non-smokers regularly exposed to secondhand smoke, they should ensure that they meet the RDA for vitamin C.

Babies fed evaporated or boiled milk

Most babies in developed countries are fed breast milk and infant formula, providing adequate amounts of vitamin C. For many reasons, it is not recommended to feed babies evaporated or boiled cow's milk. This practice can lead to vitamin C deficiency because cow's milk naturally contains very little vitamin C, and heat can destroy vitamin C.

Inpiduals with limited food persity

Although fruits and vegetables are the best sources of vitamin C, many other foods contain small amounts of this nutrient. Therefore, with a varied diet, most people should be able to meet the RDA for vitamin C or at least get enough to prevent scurvy. Some people with limited dietary persity, such as the elderly, the self-catering poor, people who abuse alcohol or drugs, food addicts, people with mental illness, and sometimes children, may not get enough vitamin C.

People with malabsorption and some chronic diseases

Some medical conditions can reduce the absorption of vitamin C and/or increase the amount needed by the body. People with severe intestinal malabsorption and some cancer patients may be at risk of vitamin C deficiency. Low vitamin C concentrations may also occur in patients with end-stage renal disease on chronic hemodialysis.

Health risks of excess vitamin C

Vitamin C has low toxicity and is not believed to cause serious side effects at high intakes. The most common complaints are that vitamin C is not absorbed in the gastrointestinal tract, leading to diarrhea, nausea, abdominal cramps, and other gastrointestinal disturbances. In postmenopausal women with diabetes participating in the Women's Health Study, supplemental (but not dietary) vitamin C intake (at least 300 mg/day) was significantly associated with an increased risk of mortality due to cardiovascular disease.