Vitamin C supplementation

Vitamin C can be administered as pure L-ascorbic acid or through mineral ascorbates (ascorbic acid salts). These salts are neutralized and, therefore, much less acidic than other forms of ascorbic acid. Mineral ascorbates are recommended for people who experience gastrointestinal problems (stomach pain or diarrhea) with ascorbic acid. When ascorbic acid mineral salts are ingested, both the ascorbic acid and the minerals are apparently well absorbed, so it is important to consider the dose of the mineral accompanying the ascorbic acid when large amounts of mineral ascorbates are ingested.

Low-quality vitamin C dietary supplements can contain inactive stereoisomers (a similar but biologically inactive molecule). Despite these small differences, ascorbic acid stereoisomers are inactive in the body, given that the enzymes specifically recognize L-ascorbic acid. Erythorbic acid (D-isoascorbic acid) differs in the spatial configuration in the fifth carbon atom and has less than 5% of the activity of biological vitamin C.

Foods with vitamin C

The best sources of vitamin C are generally fruits and vegetables, although it is also found in some meats, particularly liver. As for plants rich in vitamin C, this depends on the plant variety, the type of soil where it is grown, weather conditions, storage conditions and, above all, the preparation method (Anonymous 2009).

With respect to animal sources, most of the meat consumed in the human diet is muscle, rather than liver, animal sources are not as useful as sources of vitamin C. Thus, while the vitamin is present in human breast milk and also cow milk, processes such as pasteurization reduce the concentration to trace amounts (Clark 2007).

Vitamin C is very sensitive to light and heat and breaks down chemically under certain conditions. Thus, the vitamin C concentration falls over time in proportion to the storage temperature, and cooking can reduce the vitamin C content of vegetables by up to 60% (Allen and Burgess 1950). Long cooking times degrade the vitamin even more, particularly when the pots used contain copper, which catalyzes degradation (Anonymous 2005). In contrast, research has demonstrated that fresh fruit stored in the refrigerator for a few days loses very few nutrients (Hitti 2006).

The common plant foods with the highest vitamin C content are the following:

• Peppers (very high content), parsley, broccoli, cabbages, watercress, spinach, asparagus, chard, onions, and tomatoes.
• Kiwis, strawberries, oranges, lemons, grapefruits, papayas, mangoes, melons, mandarin oranges, and raspberries.

The foods with the highest bioflavonoid content include the following:

• Fruits: blueberries, black currants, blackberries, strawberries, grapes, cherries, apples, oranges, grapefruits, lemons, etc.
• Vegetables and herbs: chard, onions, broccoli, parsley, celery, thyme, etc.
• Legumes: soybeans, etc.
• ..
• White and green tea, red wine, etc.

In general, the bioavailability of bioflavonoids is low.

Intake and deficiencies

Vitamin C has antioxidant action by donating electrons for several enzyme systems, inhibits lipid peroxidation, and has anti-inflammatory and heavy metal detoxification action. The antioxidant activity depends on the presence of glutathione (Padayatty, Katz et al. 2003; Block, Jensen et al. 2008; Block, Jensen et al. 2009).

• Vitamin C deficiency is common when there are associated risk factors, in chronic diseases, and in the elderly.
• Low vitamin C levels are common in diabetes and asthma.
• In high blood pressure, dyslipidemia, asthma, heart disease, COPD, and respiratory infections, vitamin C can help improve their control and evolution.
• Vitamin C needs the “team” of basic nutrients to achieve its maximum therapeutic potential in chronic diseases.
• Long-term doses of vitamin C should not exceed 1,500 mg/day.
• In supplements, it is preferable to use mineral ascorbate and ascorbyl palmitate. Adding bioflavonoids can improve its action, although it may be better to supply these through foods.
• Vitamin C has an excellent safety profile, with no side effects, in the recommended forms and doses.

Vitamin C deficiency is common when there are associated risk factors, in chronic diseases, and in the elderly.

Intake. The Vitamin C concentration depends on external inputs. Developed societies generally consume sufficient vitamin C to prevent scurvy. In 2004, a survey conducted in Canada found that Canadians over the age of 19 had nutritional intakes of vitamin C of 133 mg/day in men and 120 mg/day in women (Anonymous 2006), both of which are above the PRI. It should be noted that in humans, all the symptoms of scurvy caused by diets poor in vitamin C can be reverted at doses as low as 10 mg/day.

15% of the population consumes less than the recommended daily amount, which is 75 mg for women and 90 mg for men. The National Diet and Nutrition Survey (UK) found a vitamin C deficiency in 38% of the population over the age of 65 (Bates et al., 1999).

Increased needs. Vitamin C depletion is higher in people who smoke, drink alcohol, exercise heavily, are elderly, or have a chronic disease. Chronic inflammation increases vitamin C degradation. The plasma concentration of ascorbate in a patient with oxidative stress is lower than in a healthy individual (less than 45 µmol/L in the former case compared to 61,4-80 µmol/L in the latter (Bjelakovic, Nikolova et al. 2007).

The vitamin C intake needed to prevent chronic diseases is higher than that required to prevent scurvy (Anonymous, 2010).

Nutrients. Given the preference of GLUT transporters for hexoses, consumption of very sugary foods slows down absorption of the vitamin (Wilson 2005). In any case, absorption rates range from 70% to 90% typically.

Influence of common medications. Oral contraceptives, non-steroid anti-inflammatory drugs (NSAIDs), furosemide, and corticosteroids can accentuate a marginal vitamin C deficiency.

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Reference values

DRI, NRV, UL for vitamin C

The DRI in the United States is 90 mg/day and no more than 2,000 mg/day. The basic consensus is that a balanced diet without supplementation contains sufficient vitamin C to prevent scurvy in an adult with no special requirements (e.g. pregnant women and smokers are two groups that need slightly higher intake) (Anonymous).

The NRV for ascorbic acid is 80 mg. The PRI is 60 mg for adult men and women.

Vitamin C is one of the most harmless vitamins. It has no established UL currently.

Large doses taken all at once (on the order of thousands of milligrams) can induce diarrhea in healthy adults. A contraindication for high doses of vitamin C is that this vitamin increases iron absorption (Fleming, Tucker et al. 2002). This can be a problem in people with metabolic disorders related to this metal, such as hemochromatosis. Likewise, in subjects with enzyme deficiencies, for example of glucose-6-phosphate dehydrogenase, ingestion of highly oxidizing substances like very high doses of vitamin C can lead to hemolytic anemias (Cook and Reddy 2001). Lastly, it should be noted that the suggestion that vitamin C causes kidney stones (Goodwin and Tangum 1998) is not sufficiently demonstrated (Naidu 2003).

NRV: Nutrient Reference Value. These are the daily amounts recommended for vitamins and minerals (micronutrients only) considered sufficient in the European Union to prevent a deficit in most healthy individuals in the population. They are the values used for labeling and claims.

PRI: Population Reference Intake. These are the reference values for a specific population group, defined as the amount of energy and/or nutrients (macronutrients and micronutrients) recommended to cover the nutritional needs of practically the entire population. They refer to healthy population groups. The values are expressed per person per day, as a 15-day average. To account for individual differences in digestive and metabolic processes, the PRI figure used for each nutrient is the average plus twice the standard deviation (except for energy, for which the average is used), thereby including almost all healthy individuals in the group (97.5%).

UL: Tolerable Upper Intake Level: the maximum level of total daily intake of a nutrient in a context of long-term or chronic consumption which does not pose a risk to health.