Diet and Nutrition


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
Helps in production of photo-sensitive substance (rhodopsin) in retina, which is important for night vision
Promotes growth and development
Maintains healthy skin, mucous membrane and normal function of immune system
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
Dry skin
Hair loss
Liver damage
Vitamin D
Helps body absorb calcium and phosphorus, so as to maintain bone growth
Maintains the balance of calcium in blood
Egg yolk
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
Acts as antioxidant which protects cell membrane from oxidative damage
Maintains 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
Headache, dizziness
Vitamin K
Helps blood clotting and prevent excessive bleeding
Dark green vegetables e.g. spinach, broccoli
Soya beans
Excessive bleeding may occur due to difficulty in blood clotting
Premature infants: liver damage
Helps produce cells and red blood cells
Spinach, broccoli
Kidney beans
Orange, papaya
Megaloblastic anaemia
Vitamin B1
Helps in carbohydrate metabolism and enables the body to get energy from foods
Maintains normal function of nervous system
Fish e.g. tuna
Beans e.g. black beans
Brown rice
Wernicke encephalopathy
Korsakoff’s psychosis
Vitamin B2
Helps in protein and fat metabolism and enables the body to get energy from foods
Maintains the health of mucus membranes, skin, eyes and nervous system
Helps produce coenzymes which assist in energy production
Spinach, broccoli
Nut e.g. almond
Angular stomatitis
Vitamin B3
Helps in carbohydrate and fat metabolism and enables the body to get energy from food
Brown rice
Whole wheat bread
Seed e.g. sunflower seed, pumpkin seed
Vitamin B6
Helps in protein metabolism
Helps produce heme
Helps in nerve impulse transmission
Maintains normal function of immune system
Weakened immune system
Peripheral neuropathy
Vitamin B12
Helps produce red blood cells
Maintains healthy nervous system
Helps in protein metabolism
Megaloblastic anaemia
Vitamin C
Helps produce collagen and maintain the health of blood vessels, connective tissue and cartilage
Helps the absorption of non-heme iron
Acts as antioxidant
Maintains normal function of immune system
Citrus fruits e.g. mandarin orange, orange, grapefruit, lemon
Kiwi fruit
Green pepper
Scurvy (gum bleeding, tooth loss, fatigue, bone pain, etc.)

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 adequate and appropriate amount of 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 May 2021)

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