How many times have we heard that vitamins are essential nutrients that should be present in our everyday diet? Today we shall take a look at these essential nutrients!
What Are Vitamins?
Vitamins are compounds that the body cannot synthesize, so they must be in the diet. They do not share the same molecular structure, unlike the EAAs and the EFAs and they are required in trace quantities.
Vitamins carry out a variety of functions (as listed below) and help in the prevention of specific deficiency diseases.
- Vitamin A: Helps in the proper functioning of the retina in the eye and epithelial tissues
- Vitamin D: Helps to stimulate calcium uptake from the gut and its deposition in bone.
- Vitamin E: Acts as an antioxidant to protect cells from damage caused by free radicals.
- Vitamin K: Helps in the formation in the liver of substances that promote blood clotting.
- Vitamin C: Also known as absorbic acid, it helps in the formation of collagen and the proper functioning of the skin and mucous membranes. It also stimulates the absorption of iron from the gut and maintains cartilage and bones.
Vitamin A, or retinol, is not widely distributed in food. It is in some animal foods such as milk, eggs, liver and fish-liver oils as well as in some fruits like mango and papaya. Related compounds such as carotenoids (example β-Carotene) are in a wide variety of vegetables like cabbage, carrots and spinach.
β-Carotene is converted in the body into retinol. In well-nourished people, the liver stores enough Vitamin A to last one or two years. It is stored in the liver because the vitamin is toxic in high concentrations.
Children with Vitamin A deficiency often have dry, rough skin, inflammation of the eyes, a drying or scarring of the cornea and cannot see in dim light. Rod cells in the eye’s retina detect light of low intensity, for example, in late evening and at night. They convert Vitamin A into a pigment, rhodopsin, which is bleached when light enters the eye. Rod cells resynthesize rhodopsin, but if there is a deficiency of the vitamin, rod cells can no longer function and night blindness is the result.
Epithelial cells use retinol to make retinoic acid, an intracellular messenger used in cell differentiation and growth. Without retinoic acid, epithelia are not maintained properly and the body becomes susceptible to infections, particularly measles and infections of the respiratory system and gut.
Children who are fed diets based mainly on cereals (like maize, rice or wheat) with small quantities of meat or fresh vegetables are at risk of Vitamin A deficiency, which is thought to be responsible for half a million cases of childhood blindness worldwide (approximately 40- 50 % of the total). Millions of more children receive just enough Vitamin A to stave off blindness but not enough to maintain either their immune system or their epithelia.
This is sometimes known as the “sunshine vitamin.” If the skin receives sufficient sunlight then the body can make enough Vitamin D, so it is not really needed in the diet. For example, even though people from many countries do no receive much sunlight in the winter, the amount made in the summer months is enough to last the rest of the year because Vitamin D is stored in muscles and fat.
The RDA for people confined indoors and for those whose religion requires them to not expose any skin in public is ten µg per day. Darker skin produces less Vitamin D when compared to lighter skin at the same levels of sun exposure, so dark-skinned people in temperate countries must also ensure that they receive enough Vitamin D in their diet, or spend more time outdoors. Food such as eggs and oily fish are rich in Vitamin D and margarine and low fat spreads are fortified with it. Supplements are available for children and pregnant and lactating women.
Enzymes in the liver and kidney convert Vitamin D into an active form, known as “active Vitamin D”, which acts as a hormone to stimulate epithelial cells in the intestine to absorb calcium. It does this by entering the cells and activating the genes responsible for the production of a calcium-based substance, calbindin. This mode of action is typical of steroid hormones, of which Vitamin D is one.
Did you know that a deficiency of Vitamin D in children leads to rickets? In adults, it is called osteomalacia, a progressive softening which makes the bones susceptible to fracture.
So, that’s all for today, but don’t forget to share your comments and come back for part 2!