VITAMIN C (Ascorbate, ascorbic acid) VITAMIN C (Ascorbate, ascorbic acid)Common Uses
Nutritional supplement for arthritis, allergy, epilepsy, cancer prevention, immune support
Vitamin C is a water-soluble vitamin that is required by people and some animals. Humans and certain animals (such as guinea pigs and monkeys) lack the enzyme L-gulonolactone oxidase needed for the formation of vitamin C. Dogs and cats possess this enzyme and can therefore synthesize vitamin C. As such, dogs and cats do not have a specific dietary requirement for this vitamin. Many doctors, however, will supplement with vitamin C during times of stress and illness (as larger amounts of vitamin C may be required during these times).
Ascorbic acid is a term often used interchangeably with vitamin C. While ascorbic acid (as well as ascorbate and other terms) is often used synonymously with vitamin C, this is not technically correct. Ascorbic acid (discovered in 1928, when Albert Szent-Gyorgyi isolated the active ingredient in fruits and called the “anti-scorbutic principle”) is the antioxidant fraction of vitamin C. Simply supplementing ascorbic acid is not the same as supplying vitamin C. Holistic veterinarians usually prefer natural vitamin C supplementation when indicated, although studies using the complementary therapy called orthomolecular medicine have shown benefit to using ascorbate in helping pets with a variety of medical disorders. A novel product called Ester-C has also shown benefit in pets (discussed to follow).
Vitamin C functions as an antioxidant and free radical scavenger, is used for normal repair of tissues, is required for adrenal gland function, is used for collagen synthesis, and is needed for maintaining healthy gums. It is needed for the metabolism of several B vitamins, including folic acid and the amino acids tyrosine and phenylalanine. Vitamin C is needed for norepinephrine (a nerve transmitter) synthesis as well as for cholesterol synthesis.
This vitamin assists in providing some protection against cancer and infection and enhances immunity. Hemoglobin synthesis requires vitamin C; deficiency can cause anemia.
Because vitamin C is so vital for the synthesis of the connective tissue collagen, which is an integral part of cartilage, it is often prescribed for pets with arthritis (and various forms of vitamin C or ascorbate are often included in various nutritional supplements for pets with arthritis).
To have normal collagen metabolism, vitamin C is required for the conversion of proline to hydroxyproline and for the conversion of lysine to hydroxylysine. These reactions take place after proline and lysine are incorporated into the connective tissue.
Vitamin C also protects against unnecessary blood clotting and bruising and aids in healing of wounds; vitamin C deficiency causes slow scar formation.
Ascorbic acid is a precursor of oxalate. It has been suggested that additional ascorbic acid should not be fed to pets prone to oxalate bladder stones. However, at least in people, there is no evidence that high levels of ascorbic acid actually increase oxalate production.
Vitamin C appears to work synergistically as an antioxidant with vitamin E. Vitamin C appears to attack free radicals, those chemicals produced as a by-product of cell metabolism, in cellular fluids, whereas vitamin E attacks the free radicals in the cell membranes.
In people, vitamin C has been recommended for numerous conditions, including colds, cataracts, macular degeneration, cancer prevention and treatment, heart disease prevention, hypertension, asthma, low sperm count, bedsores, Alzheimer’s disease, diabetes, hepatitis, herpes, insomnia, osteoarthritis, Parkinson’s disease, periodontal disease, preeclampsia, rheumatoid arthritis, ulcers, allergies, general antioxidant, bladder infections, menopausal symptoms, migraine headaches, and nausea.
Ascorbic acid scavenges nitrates, which can reduce nitrosamine-induced cancers.
There is some evidence that supports using vitamin C supplements to help colds, slightly improve asthma, and reduce the risk of macular degeneration and cataracts.
In people, vitamin C deficiency causes scurvy with the clinical signs of swollen, painful joints, abnormal wound healing, bleeding gums, and pinpoint hemorrhages under the skin. Vitamin C deficiency, while common in non-human primates (monkeys) and guinea pigs, does not occur in dogs and cats.
Regular use of vitamin C may reduce the risk of cataracts, probably by fighting free radicals that damage the lens of the eye. In an observational study of 50,800 nurses followed for 8 years, it was found that people who used vitamin C supplements for more than 10 years had a 45% lower rate of cataract development. However, unlike the case with other supplements, diets high in vitamin C were not found to be protective; only supplemental vitamin C made a difference. This is the opposite of what has been found with vitamin C in the prevention of other diseases, such as cancer.
It has been suggested that vitamin C may be particularly useful against cataracts in people with diabetes, because of its influence on sorbitol, a sugar-like substance that tends to accumulate in the cells of diabetics. Excess sorbitol is believed to play a role in the development of diabetes-related cataracts, and vitamin C appears to help reduce sorbitol buildup.
Vitamin C levels in the blood have been found to be low in people with diabetes. When vitamin C levels were adequate, the regulation of insulin improved, as vitamin C has been shown to enhance insulin action and improve glucose and lipid metabolism. Therefore, vitamin C supplementation may benefit both insulin-dependent and non-insulin-dependent diabetics. It is unknown if this is the case in diabetic pets, although vitamin C has been recommended for pets with diabetes.
There is also good evidence for using ascorbate for people with gingivitis. Evidence for its effectiveness in treating other conditions is highly preliminary at best.
In people, aspirin, other anti-inflammatory drugs, corticosteroids, and tetracycline-family antibiotics can lower body levels of vitamin C. The same may be true of pets; vitamin C given to pets treated with the medications mentioned above is not harmful and might be helpful.
Pets are often treated with additional vitamin C or ascorbate compounds for various illnesses. Both intravenous and oral supplementation are used, although controlled studies are lacking showing the effectiveness of giving vitamin C or ascorbate compounds for most conditions.
Orthomolecular medicine, utilizes high doses of antioxidants to help pets with a variety of medical conditions. Ascorbate has shown effectiveness (when combined with other antioxidants) in clinical cases of pets with epilepsy, atopic dermatitis, feline leukemia virus, periodontal disease, and osteoarthritis.
Ester-C Chelated Mineral Blend for Animals is a patented, non-acidic form of calcium ascorbate that contains the essential minerals calcium, magnesium, manganese, and zinc bound in a pH neutral complex along with vitamin C metabolites (naturally occurring dehydroascorbate and threonate) that enhance the absorption of vitamin C. This form of ascorbate is often preferred by some veterinarians as Ester-C permits rapid absorption from the gastrointestinal tract (resulting in less chance of gastrointestinal disturbances such as diarrhea). Also, Ester-C produces higher serum levels, higher WBC levels, less oxalate excretion, and less urinary ascorbate loss than ascorbic acid.
In numerous clinical trials and studies in the U.S. and Norway, Ester-C mineral ascorbates have been shown beneficial in alleviating signs of non-specific lameness in dogs and degenerative joint disease (DJD) in horses and chronic obstructive pulmonary disease (COPD) in horses. Specifically, a study done in arthritic dogs showed that 62% of dogs receiving the Chelated Mineral Blend given at a dosage of 45 mg/kg of body weight twice daily experienced improved locomotion within 5 to 8 days of usage (44% of dogs on plain ascorbic acid at the same dosage showed some improvement, and two dogs experienced mild gastrointestinal disturbances).
Citrus fruits, green vegetables, berries, broccoli, brussels sprouts, collard greens, mustard greens, spinach, chard, turnip greens, red chili peppers, sweet peppers, kale, parsley, watercress, cauliflower, cabbage, and strawberries are good sources of vitamin C, as are green foods, alfalfa, herbs, rose hips, dandelion, fennel, and slippery elm.
In people, good evidence suggests that there is no reason to take more than 200 mg of vitamin C daily (which is approximately 10 to 100 times less than the amount recommended by vitamin C proponents). The reason is that if people consume more than 200 mg daily (researchers have tested up to 2,500 mg), their kidneys begin to excrete the excess at a steadily increasing rate, matching the increased dose. Additionally, their digestive tracts also stop absorbing it well at higher doses. The net effect is that even with increasing doses, blood levels of vitamin C don’t increase. There is no evidence to suggest the maximum dose at which pets stop absorbing vitamin C or begin excreting extra vitamin C (orthomolecular therapy uses higher doses than 200 mg).
As dogs and cats manufacture their own vitamin C, there is no AAFCO recommendation for including vitamin C in the diets or supplements of dogs and cats. Many natural foods will use vitamin C (often supplied as rose hips) or various forms of ascorbate (or ascorbic acid) as a natural preservative. Contacting the manufacturer will allow the owner to determine the level in the food, although pets requiring vitamin C will need more than the amount added to the food as a natural antioxidant.
Vitamin C is a safe vitamin. High oral doses (which vary from pet to pet) may cause people and pets to develop diarrhea. This is the “bowel tolerance” dose; in orthomolecular medicine, vitamin C is often dosed to bowel tolerance.
In people, high-dose vitamin C can cause copper deficiency and excessive iron absorption. There have also been warnings that long-term vitamin C treatment can cause kidney stones, but in a large-scale study the people who took the most vitamin C (over 1,500 mg daily) actually had a lower risk of kidney stones than those taking the least amounts. Nonetheless, people with a history of kidney stones and those with kidney failure who have a defect in vitamin C or oxalate metabolism should probably restrict vitamin C intake to approximately 100 mg daily. While there is no evidence that stone formation increases in people or pets supplemented with vitamin C, talk with your veterinarian before adding extra vitamin C if your pet is prone to urinary stones.
Vitamin C may also reduce the blood-thinning effects of Coumadin (warfarin) and heparin.
Vitamin C may increase the blood levels of some drugs, such as aspirin and other salicylates.