PLEASE NOTE - I did NOT write this - I am copying and pasting from Linda Hornberger's FB Group. But it is very concise and easy to follow.
Vitamins (1 of 6)
Next to energy, vitamins are one of the most important aspects of food. Vitamins are organic molecules that the body needs in tiny amounts to help with many of the enzymatic processes. They are not fat, carbohydrate, nor protein and are not used for energy or as structural components. Most cannot be synthesized by the body.
Vitamins can be divided into two groups: fat-soluble, water-soluble.
Vitamins (1 of 6)
Next to energy, vitamins are one of the most important aspects of food. Vitamins are organic molecules that the body needs in tiny amounts to help with many of the enzymatic processes. They are not fat, carbohydrate, nor protein and are not used for energy or as structural components. Most cannot be synthesized by the body.
Vitamins can be divided into two groups: fat-soluble, water-soluble.
Fat-soluble vitamins are A, D, E, and K. They are digested and
absorbed in ways similar to fats and are excreted in feces through the
bile. Excesses are stored in the liver. Because they are stored, the
fat-soluble vitamins, and especially A and D, are more likely to build
to toxic levels than water-soluble vitamins. Also because they are
stored, deficiencies develop slowly.
Water-soluble vitamins are C and the B-complex vitamins. These are absorbed passively in the small intestine and excreted in the urine. With the exception of cobalmin (B12), the other water-soluble vitamins are not stored in the body. Hence, while they have a low risk of developing toxic levels, they have a better chance of developing deficiencies than do fat-soluble vitamins.
The photo shows a summary of signs of deficiency, signs of excess, and the food sources for each of the vitamins. We will discuss each in turn.
Water-soluble vitamins are C and the B-complex vitamins. These are absorbed passively in the small intestine and excreted in the urine. With the exception of cobalmin (B12), the other water-soluble vitamins are not stored in the body. Hence, while they have a low risk of developing toxic levels, they have a better chance of developing deficiencies than do fat-soluble vitamins.
The photo shows a summary of signs of deficiency, signs of excess, and the food sources for each of the vitamins. We will discuss each in turn.
Vitamins (2 of 6)
The first vitamin we will look at is Vitamin A. Vitamin A is actually several compounds, retinol, retinal, and retinoic acid, with retinol being the most biologically active form. In the body, vitamin A is involved in vision, bone growth, reproduction and epithelial tissue (the tissue that lines body cavity, organs, and comprises much of the glands).
Regarding vision, the retinal combines with a protein to form rhodopsin, which is the light-sensitive pigment found in the rods of the retina. [Rods are the part of the retina which is responsible for low-light, black and white vision.] The rhodopsin splits apart when exposed to light, releasing energy that is transmitted by the nerves. It then regenerates in the dark. With a deficiency of vitamin A, the rods become increasingly insensitive to light, eventually leading to night blindness.
Regarding epithelial tissue, vitamin A is necessary for the production and differentiation of the cells and for the production of mucoproteins, found in some of the mucous secreted by the body. This mucous, in the respiratory and gastrointestinal tract is an barrier against infection. With a deficiency of vitamin A, lesions occur which can then lead to increased infections.
Regarding bone and tooth development, vitamin A is important for the epithelial cartilage and for osteoclast activity, which are the cells responsible directly for bone growth.
Regarding reproduction, vitamin A has been shown to be important for the production of sperm and for normal estrous cycles.
In most animal, vitamin A is converted from carotenoids, the yellow orange pigments in plants. Cats, however, lack the enzyme (or are very deficient in it) which converts the carotenoids. Thus, cats MUST consume vitamin A. Fish oils, milk, liver, and egg yolk are all sources for pre-formed vitamin A which cats can use.
Interestingly, lutein, one of the carotenoids, and beta-carotene do actually have a role in cats. It seems these two compounds have a function in cell-mediated and humoral immune response. [Regarding this, see https://www.ncbi.nlm.nih.gov/pubmed/10713345
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