Most species do not require vitamin C as an essential ingredient in their diets, but there are some notable exceptions.
The most notable species requiring vitamin C is us. Along with humans, nonhuman primates, guinea pigs, bats, and some fish and bird species require vitamin C as they cannot produce it themselves; therefore, they must consume vitamin C in the foods that they eat to meet this requirement. These species lack the enzyme (L-gulonolactone oxidase) that converts glucose and galactose into ascorbic acid. For those species that can synthesize vitamin C, this enzyme is normally present in the liver of mammals and in the liver or kidneys of other species.
Sailors and scurvy
Determining that vitamin C was a required nutrient was finally deduced after sailors would develop scurvy, which included symptoms such as lethargy, painful joints, gum disease, and eventually death. This group was particularly vulnerable due to perishable fruits and vegetables not being available for long voyages at sea. It was eventually understood that citrus fruits helped correct or prevent scurvy, but it took many years before this was linked to vitamin C.
The importance of vitamin C in humans
Ascorbic acid is an important player in collagen and carnitine synthesis, as an antioxidant, and mineral metabolism. Like other water-soluble vitamins, there is no body tissue storage of vitamin C. This means that species requiring vitamin C must consume it regularly to maintain circulating levels. Fresh foods high in vitamin C include citrus fruits (notably oranges and lemons), bell peppers, broccoli, strawberries, cantaloupe, kale, tomatoes and organ meats. Vitamin C is relatively non-toxic, even at very high doses. High doses of vitamin C in humans are believed to reduce the severity of common cold symptoms but do not prevent colds. The most notable side-effects of very high doses of vitamin C include gastrointestinal upset and diarrhea.
Vitamin C for pets in small animal and pet bird diets
Naturally occurring ascorbic acid is highly sensitive to high temperatures, pH, oxygen, and pressure. Unfortunately, high temperatures and pressure also generally occur during the manufacture of many animal diets. Most small animal and pet bird diets contain at least some pellets or extruded particles. Pelleting and extrusion processes involve heat and pressure, although to different degrees. Because the source of vitamin C within a diet usually comes from the pellets/extruded kibble, finding a heat-and-storage-stable vitamin C source was important to the animal feed industry.
Longer shelf life for small-pet food
For those species requiring vitamin C in their diet, the often told rule of thumb is that it is recommended to feed a diet within 3 months of manufacture. This was due to the fact that previously used vitamin C sources would degrade during processing and quickly over time. Modern technology has allowed us to significantly increase the shelf life of vitamin C using a stabilized version, L-ascorbyl-2-polyphosphate. The phosphate is broken off during digestion, making the ascorbic acid completely available to the animal. This ingredient is heat stable and shelf stable, making it the perfect option to ensure your pet is getting all the vitamin C it needs.