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Vitamins are classified as either water-soluble or fat-soluble. 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 ...
With few exceptions, like some vitamins from B-complex, hypervitaminosis usually occurs with the fat-soluble vitamins A and D, which are stored, respectively, in the liver and fatty tissues of the body. These vitamins build up and remain for a longer time in the body than water-soluble vitamins. [2] Conditions include: Hypervitaminosis A
Vitamin D is a group of structurally related, fat-soluble compounds responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, along with numerous other biological functions. [1] [2] In humans, the most important compounds within this group are vitamin D 3 (cholecalciferol) and vitamin D 2 (ergocalciferol). [2] [3]
Vitamin E is a group of eight compounds related in molecular structure that includes four tocopherols and four tocotrienols. The tocopherols function as fat-soluble antioxidants which may help protect cell membranes from reactive oxygen species. Vitamin E is classified as an essential nutrient for humans.
Vitamin A is a fat-soluble vitamin that is an essential nutrient. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol , retinyl esters , and several provitamin (precursor) carotenoids , most notably β-carotene ( beta - carotene ).
Each gram of fat when burned or metabolized releases about nine food calories (37 kJ = 8.8 kcal). [5] Fats are also sources of essential fatty acids, an important dietary requirement. Vitamins A, D, E, and K are fat-soluble, meaning they can only be digested, absorbed, and transported in conjunction with fats.
Thiamine was the first of the water-soluble vitamins to be isolated. [72] The earliest observations in humans and in chickens had shown that diets of primarily polished white rice caused beriberi, but did not attribute it to the absence of a previously unknown essential nutrient. [73] [74]
Apolipoprotein synthesis in the intestine is regulated principally by the fat content of the diet. Apolipoprotein synthesis in the liver is controlled by a host of factors, including dietary composition, hormones (insulin, glucagon, thyroxin, estrogens, androgens), alcohol intake, and various drugs (statins, niacin, and fibric acids). ApoB is ...