Diet and Nutrition

VITAMINS

Food nutrients include carbohydrates, protein, fat, vitamins and minerals. The body needs to obtain appropriate amount of vitamins from food in order to maintain normal functions of cells and organs, and to promote growth and development. Any deficiency or overdose of vitamins could have adverse side effects.

Functions and Categories

• Vitamins have various functions that help to regulate metabolism, to prevent chronic diseases (such as heart disease and cancer), and to maintain normal appetite, mental health and immunity. Basically vitamins can be classified into two categories:
  
  

  (1)	Fat-soluble vitamins
  	* Include vitamins A, D, E and K. They can dissolve in fats and be absorbed along with fats in the diet * Excess fat-soluble vitamins are stored in the liver and will not be eliminated from the body
  (2)	Water-soluble vitamins
  	* Include vitamins B and C. They can dissolve in water * Excess water-soluble vitamins are excreted through urine

  
  
• The amount of vitamins in food is affected by the ways in which food is stored or cooked. Vitamins A and C and some vitamins B can be destroyed under strong light, so food rich in those vitamins should be stored in dim places or in the fridge. Vitamin C and some vitamins B are soluble in water and can be destroyed under heat. Therefore, we should avoid soaking the food in water or cooking the food for too long.
  

Vitamin	Function(s)	Food sources	Health effect(s) of deficiency	Health effect(s) of overdose
Vitamin A	Help in production of photo-sensitive substance (rhodopsin) in retina, which is important for night vision Promote growth and development Maintain healthy skin, mucous membrane and normal function of immune system	Liver Fish liver oil Oily fish e.g. salmon, mackerel Egg yolk Foods containing carotenoids e.g. carrot, spinach, broccoli, papaya, tomatoes, sweet potatoes * β-carotene (one kind of carotenoids) can transform into vitamin A in the body	Night blindness, dry eyes Epithelial tissue keratinization Retard growth Impair immune function	Dry skin Hair loss Liver damage
Vitamin D	Help body absorb calcium and phosphorus, so as to maintain bone growth Maintain the balance of calcium and phosphorus in blood Maintain normal function of immune system	Egg yolk Liver Fish liver oil Oily fish e.g. salmon, mackerel Skins produces vitamin D when exposed to sunlight	Children: rickets Adults: osteomalacia	High calcium levels in blood and urine which increase the risk of calcification of soft tissue
Vitamin E	Act as antioxidant which protects cell membrane from oxidative damage Maintain normal function of immune system	Plant oil e.g. corn oil, sunflower oil Nut e.g. almonds Seed e.g. sunflower seeds Dark green vegetables e.g. spinach, broccoli	Premature infants: haemolytic anaemia	High dosage of Vitamin E may antagonize the effect of Vitamin K and lead to difficulty in blood clotting
Vitamin K	Help blood clotting and prevent excessive bleeding Participate in bone metabolism	Dark green vegetables e.g. spinach, broccoli Soya beans	Excessive bleeding may occur due to difficulty in blood clotting	Uncommon
Folate	Help produce cells and red blood cells	Spinach, broccoli Egg Kidney beans Orange, papaya	Megaloblastic anaemia	Long term use of high dosage of folate can affect zinc absorption Masking undiagnosed Vitamin B12 deficiency
Vitamin B1	Participate in carbohydrate metabolism and enables the body to get energy from foods Maintain normal function of nervous system	Pork Fish e.g. tuna Beans e.g. black beans Brown rice	Beriberi Wernicke encephalopathy Korsakoff’s psychosis	Uncommon
Vitamin B2	Participate in protein and fat metabolism Maintain the health of mucus membranes, skin, eyes and nervous system Help produce coenzymes which assist in energy production	Liver Milk Egg Meat Spinach, broccoli Nut e.g. almond	Glossitis Angular stomatitis Cheilosis	Uncommon
Vitamin B3	Participate in carbohydrate, protein and fat metabolism Help produce coenzymes which assist in energy production	Meat Fish Brown rice Whole wheat bread Seed e.g. sunflower seed, pumpkin seed	Pellagra	Flushing
Vitamin B6	Participate in carbohydrate, protein and fat metabolism Help produce heme Help in nerve impulse transmission Maintain normal function of immune system	Meat Fish Banana Potatoes Nut e.g. hazelnuts	Anaemia Depression Weakened immune system	Peripheral neuropathy
Vitamin B12	Help produce red blood cells Maintain healthy nervous system Help in protein metabolism	Milk Fish Egg Liver Meat	Megaloblastic anaemia	Uncommon
Vitamin C	Help produce collagen and maintain the health of blood vessels, connective tissue and cartilage Help the absorption of non-heme iron Act as antioxidant Maintain normal function of immune system	Citrus fruits e.g. mandarin orange, orange, grapefruit, lemon Strawberry Kiwi fruit Guava Broccoli Green pepper	Scurvy (gum bleeding, tooth loss, fatigue, bone pain, etc.)	Diarrhoea

Should we take vitamin supplements?

There are various kinds of vitamin supplements available in the market. Should we take these "tonics" to maintain good health?

We should maintain a balanced diet and should not be a picky eater. Eating according to the “Healthy Eating Food Pyramid” can provide the necessary vitamins to stay healthy.

If you need to have diet control because of any illnesses, you should consult a doctor or dietitian. Never take any vitamin pill or supplement on your own.

(Revised in June 2022)

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