The A to E of vitamins – what they are and what do they do

We’ve all heard of vitamins – for example, they’re one of the main selling point for many common foods like breakfast cereals – but how much do actually know about them? This is an A to E of vitamins – what they are, where they come from, and what they do

Vitamin A is a group of unsaturated nutritional organic compounds that includes retinol, retinal, and several provitamin A carotenoids such as beta-carotene. It has multiple functions in the human body, for example, it’s important for growth and development, for the maintenance of the immune system, and for vision (vitamin A is needed by the retina of the eye in the form of retinal). It also functions in a very different role as retinoic acid which is an important hormone-like growth factor for epithelial and other cells

B vitamins are water-soluble compounds that play an important role in cell metabolism and the synthesis of red blood cells. B vitamins (e.g. B1, B2, B3, etc.) are actually chemically distinct from each other but often coexist in the same foods. Often, in dietary supplements containing all 8 B vitaimins, thay are referred to as a ‘vitamin B complex’. When sold individually, B vitamins are more commonly referred to  supplements are referred to by the specific number or name of each vitamin, such as B1 for thiamine, B2 for riboflavin, and B3 for niacin, as examples.[1] Some are more commonly recognized by name than by number: niacin, pantothenic acid, biotin and folate.

Vitamin C is also often referred to as ascorbic acid and is found naturally in various foods such as oranges. It’s also sold as a dietary supplement as it’s believed by many to help protect again colds and flus as it is important for immune system function (note there is some evidence that regular use of supplements may reduce the duration of the common cold, but it does not appear to prevent infection). In the body it’s an essential nutrient involved in the repair of tissue and the enzymatic production of certain neurotransmitters and also functions as an antioxidant.

Vitamin D is actually a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological functions. In humans, the most important compounds in this group are vitamin D3 (also known as cholecalciferol) and vitamin D2 (ergocalciferol). The major natural source of the vitamin is synthesis of cholecalciferol in the lower layers of skin epidermis through a chemical reaction that is dependent on sun exposure (specifically UVB radiation). Only a few foods, such as the flesh of fatty fish, naturally contain significant amounts of vitamin D. In many countries, cow’s milk and plant-derived milk substitutes are fortified with vitamin D, along with many breakfast cereals. Mushrooms exposed to ultraviolet light contribute useful amounts of vitamin D. Dietary recommendations typically assume that all of a person’s vitamin D is taken by mouth, as sun exposure in the population is variable and recommendations about the amount of sun exposure that is safe are uncertain in view of the skin cancer risk.

Vitamin E is a light yellow oil, a fat soluble vitamin, that is actually a family of substances, the tocopherols and tocotrienols, collectively known as ‘tocols’. They are found in nature in both plant and animals, however, since they are biosynthesized only in photosynthetic organisms, main sources are vegetables and seed or nut oils. There were first isolated from wheat germ oil, which is still a commonly used source of Vitamin E. The primary function of Vitamin E is as an antioxidant. Vitamin E is protective because it helps reduce oxidation of lipid membranes and the unsaturated fatty acids and prevents the breakdown of other nutrients by oxygen.

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