Съдържание
Съдържание
Vitamin C, also referred to as ascorbic acid or ascorbate, has been one of the most researched vitamins over the last 50 years. A search of the scientific literature reveals that over 65,000 studies have been conducted on vitamin C in the past century.
Many scientists believe that at one time the human body had the ability to make vitamin C, but due to a genetic mutation (in the L-gulonolactone oxidase gene), we lost this capacity over time. Essentially, all species of animals, including most mammals, can make vitamin C—the exceptions are humans, monkeys, and guinea pigs as well as some bats, birds, and fish species. As a result, we humans must consume vitamin C in our diets.
Currently, the Recommended Dietary Allowance (RDA) for vitamin C is 90 mg per day for men and 75 mg per day for women. Smokers, who are 400 percent more likely to be deficient than non-smokers due to the excess oxidation caused by the cigarettes, require more to maintain healthy levels of the vitamin. The brain and adrenal glands have the highest concentrations of vitamin C at 15 to 50 times higher than those found in the blood. Vitamin C, which has antioxidant properties, is also an enzyme “co-factor” for at least eight important biochemical reactions.
While the standard Recommended Dietary Allowance (RDA) amount is sufficient to avoid conditions like scurvy, which is caused by severe vitamin C deficiencies, they are insufficient to achieve other presumed health benefits, including promoting a stronger immune system and cardiovascular, brain, and skin health. Some have suggested that this minimum vitamin C intake should be at least 200 mg per day to optimize the full benefits of vitamin C.
According to a 2004 study of Americans, 14 percent of males and 10 percent of females were vitamin C deficient. In addition, up to six percent of kids ages 12 to 17 had insufficient levels. Seventeen percent of males between ages 25 to 64 were deficient while 12 percent of females in that demographic had low blood levels. A 1999 study in Britain found that 33 percent of those 65 years of age consumed insufficient amounts of vitamin C.
A 2009 study in The American Journal of Clinical Nutrition, found that over seven percent of people age six and older were vitamin C deficient when their blood was tested. More than half of those surveyed consumed too low amounts of vitamin C-rich foods.
I’ve seen it in my practice as well. In the last five years, I diagnosed at least four patients with scurvy, a disease that was traditionally diagnosed in British sailors who had limited access to fresh fruit. My first patient with scurvy was a 40-year-old woman who smoked and admitted to a poor diet. She was concerned about her bleeding gums and easy skin bruising, and after her dentist confirmed the absence of gum disease, I ordered a blood test which confirmed a vitamin C deficiency, leading to the diagnosis of scurvy. Her bleeding gums and bruising symptoms improved after a few weeks of vitamin C supplementation. The other three patients also had significant bruising and bleeding gums as their initial symptoms.
There are two main ways vitamin C can be measured in the body. The first is a blood serum level. For women, normal levels are between 0.3-2.7 mg/dL while normal for men is 0.2-2.1 mg/dL. The second is checking vitamin C levels in white blood cells, or leukocytes. The reference range depends on the lab.
In addition to the benefits discussed above, vitamin C appears to be beneficial for those admitted to a hospital, specifically, the intensive care unit. A 2019 meta-analysis study in Nutrients, which looked at more than 18 studies and over 2,000 patients, noted that hospital patients who supplemented with vitamin C reduced their ICU stay by 8 to 18 percent compared to those who were not given vitamin C.
Various formulations are available to consumers.
Ascorbic acid is the most commonly consumed and also the least expensive form of vitamin C available. However, its slight acidic component can make it hard on the digestive system for some, especially those with stomach acid issues. Many studies use this formulation of vitamin C. While ascorbic acid is synthetically made, it is identical to the formulations found in nature. Since studies show only 30 percent of a given dose is actually absorbed, researchers have also sought other formulations that may be better absorbed in the gastrointestinal tract. Ascorbic acid is available in tablets, capsules, or as a powder. The following are mineral ascorbates.
Ascorbate and Vitamin C Metabolites (Ester-C®) is a patented formulation of calcium-ascorbate that was discovered in the 1980s. It contains a small amount of vitamin C metabolites such as calcium threonate, xylonate, and lyxonate, as well as dehydroascorbic acid. The manufacturer claims it helps improve absorption and results in higher vitamin C blood levels compared to regular ascorbic acid.
A 2008 study evaluated blood serum and leukocytes levels after ingestion of calcium ascorbate versus regular ascorbic acid. The blood serum ascorbic acid levels were equal in both groups. However, those who took the calcium ascorbate formulation had higher vitamin C leukocyte (white blood cell) levels.
Vitamin C is also combined with antioxidants known as bioflavonoids. Proponents of this formulation are drawn to the fact that vitamin C with bioflavonoids may be better absorbed. A 1988 study showed this might be the case. In the study, it was shown that vitamin C with bioflavonoids was 35 percent better absorbed when compared to the regular ascorbic acid formulation. It is also a better option for those who may develop gastric symptoms from ascorbic acid.
Liposomal vitamin C is a formulation that appears to have improved bioavailability or absorption properties. To help increase absorption, scientists have developed liposomal vitamin C, a fat-soluble covering that helps the ascorbic acid molecule pass through the digestive tract more easily. The data indicates that oral delivery of vitamin C encapsulated in liposomes results in blood concentrations of vitamin C that are greater than un-encapsulated oral formulations, such as ascorbic acid, but less than intravenous administration.
Further, a 2020 study showed that liposomal vitamin C could lower blood pressure at a lower dosage than regular vitamin C in laboratory rats.
This formulation allows vitamin C, which is normally water-soluble, to become fat-soluble. It is usually added to topical vitamin C preparations so that it can be absorbed in the skin. It is also used in suppositories and as food preservatives. It is sometimes marketed as a vitamin C ester but should not be confused with Ester-C.
Formulations of vitamin C with rose hips normally contain regular ascorbic acid. Rose hips are the fruits of rose plants and contain a high amount of vitamin C, which is well absorbed. Rose hips also contain many antioxidants, including lycopene, phenols, flavonoids, ellagic acid, and vitamin E.
Vitamin C, in all formulations, has a great safety profile. Doses up to 2,000 mg per day are commonly taken and well-tolerated. Diarrhea or loose stool is not likely unless 3,000 mg per day is exceeded. However, if a large daily dose is spread out and taken up to three times per day, digestive issues are less likely to occur.
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