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In humans there are 13 vitamins: 4 fat-soluble (A, D, E, and K) and 9 water-soluble (8 B vitamins and vitamin C). Water-soluble vitamins dissolve easily in water and, in general, are readily excreted from the body, to the degree that urinary output is a strong predictor of vitamin consumption. [ 47 ]
Vitamin C megadosage is a term describing the consumption or injection of vitamin C (ascorbic acid) in doses well beyond the current United States Recommended Dietary Allowance of 90 milligrams per day, and often well beyond the tolerable upper intake level of 2,000 milligrams per day. [1]
The ingredient is also used in body lotions to treat Tinea versicolor due to infection by a different species of Malassezia fungus. [12] Several clinical trials have assessed the use of selenium supplements in critically ill adults; however, the effectiveness and potential benefits of selenium supplementation in this context is not well ...
(Many animal species can synthesize vitamin C, but humans cannot.) Certain vitamin-like compounds that are recommended in the diet, such as carnitine , are thought useful for survival and health, but these are not "essential" dietary nutrients because the human body has some capacity to produce them from other compounds.
Vitamin K is a family of structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. [1] The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation ("K" from Danish koagulation, for "coagulation") or for controlling binding of calcium in bones and other tissues. [2]
There is evidence that the sale of dietary supplement vitamin E has decreased by up to 33% following a report showing little or no effect of vitamin E in preventing cancer or cardiovascular disease. [11] In 2022, it was the 244th most commonly prescribed medication in the United States, with more than 1 million prescriptions. [64] [65]
Feline species and dogs are practically incapable of vitamin D synthesis due to high activity of 7-dehydrocholesterol reductase, which converts any 7-dehydrocholesterol in the skin to cholesterol before it can be UVB light modified, but instead get vitamin D from diet. [195] [196] Fish do not synthesize vitamin D from exposure to ultraviolet light.
In the case of the simians, it is thought that the loss of the ability to make vitamin C may have occurred much farther back in evolutionary history than the emergence of humans or even apes, since it evidently occurred soon after the appearance of the first primates, yet sometime after the split of early primates into the two major suborders ...