Nutrition page 4
Vitamin A
Vitamin A (retinoids) is required for vision. In retina, light causes vitamin A to undergo chemical changes into electrical signals which are relayed to the brain. The brain then processes that information enabling us to interpret what we see. Vitamin A is also a critical component of the outer corneal surface as well, and in this vitamin A is regularly shed and replaced. This requires a constant supply of vitamin A to sustain renewal. Insufficient vitamin A can cause vision problems like blurriness and night blindness, potentially causing damage to your retina. Other symptoms of deficiency include dry eyes (the cornea becomes dry), and increased risk of conjunctivitis.
Sometimes known as the “anti-infection” vitamin, vitamin A also strengthens the immune system in a number of ways, preventing many diseases and infections in children. Vitamin A is vital for cells that cover our body, including the skin, nose, ear, cornea, and the insides of our airways and gut. These cells protect us by forming a physical barrier, preventing the entry of infectious microbes, and assisting mucus secretion that contains anti-microbial agents.
Vitamin A regulates immune system function. It assists the innate immune system in generating cells, such as natural killer cells, which act as the first-line of defence against invading pathogens, as well as the B and T cells of the adaptive immune system. Vitamin A is known to promote the production of antibodies, which help neutralise toxins released by bacteria, and “tag” the infectious germs for destruction by other immune cells.
There are two major sources of vitamin A. Vitamin A from animal-foods, such as in liver and eggs, are called retinoids, can be used directly by our body. Caution should be exercised as too much can be toxic. Vitamin A can also be obtained from yellow-orange vegetables and fruits (such as carrots, sweet potatoes, yellow squash, pumpkin, tomatoes, mango, pawpaw, apricots, persimmon, and rockmelons or cantaloupe) are called beta-carotenes, which are converted to retinoids as they are required. Because of this process, the risk of consuming too much is minimal when compared to animal-derived vitamin A.
B group vitamins
The B vitamins are a group of 8 water soluble vitamins. They are widely present in a range of foods, but are quite delicate and easily destroyed, for instance through alcohol consumption and cooking processes. Food processing removes much of the B vitamins, which is why white cereals (rice, bread) for instance, are less nutritious than their wholemeal counterparts.
Being water soluble vitamins, make sure that you include some foods containing these vitamins everyday, because your body cannot store them.
Vitamin B1 (thiamin)
Vitamin B1 is required for energy generation by our cells. In the brain, thiamin is involved in glucose metabolism, glucose being the preferred source of energy for neurons.
Insufficient vitamin B1 in your diet can lead to symptoms including nausea, loss of appetite, and depression, as neurons lose their function and die off. Severe vitamin B1 deficiency will lead to a condition called beriberi, causing painful and weak arms and legs, memory problems, confusion, and other nervous and mental problems. Also essential for eye cells, the eyes are affected with the condition causing abnormal eye movements and the inability of both eyes to move in the same direction.
Beriberi is common in many Asian countries where white rice is primarily eaten, and has been described in Chinese literature way back in 2600 B.C. Studies completed in Australia and the US have also found that people with lower intakes of vitamin B1 have a higher risk of developing cataracts.
Vitamin B1 is found in unrefined cereals and fresh foods, especially legumes like soybeans, green vegetables and fruit.
Vitamin B2 (riboflavin)
Vitamin B2 has numerous functions. Apart from its involvement in cell energy generation, it also acts as an antioxidant, and assists absorption of other vital nutrients like vitamins B6, folic acid, and niacin.
The lack of vitamin B2 can cause problems such as sores and swelling on the wall of the mouth and throat, and scaly skin inflammation. Vitamin B2 deficiency can also lower iron metabolism, leading to anaemia. There are a number of eye problems also associated with vitamin B2 deficiency. Symptoms include the appearance of blood vessels in the surface of the eye, and has been linked with a higher risk of developing corneal damage and cataracts.
Food sources of vitamin B2 include yeast, meat (leaner cuts), eggs, and green leafy vegetables. Vitamin B2 is sensitive to light damage, so food should be stored away from sunlight.
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