Diet & Nutrition


The basic nutrients of food include carbohydrate, protein, fat, vitamins, and minerals. The body needs to obtain appropriate vitamins from food to maintain the normal functions of cells and organs, and to promote growth and development. Any lack or excess amounts of vitamins in the body may have 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.
  • Vitamins can basically be classified into the following two categories:
    (1) Fat-soluble vitamins
    * Include Vitamins A, D, E and K; dissolve in fats; and are absorbed with the help of fats that are in the diet
    * Excessive 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, and dissolve in water
    * Excessive amount of water-soluble vitamins are excreted through urine and sweat.

  • 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, and thus we should avoid
    1. washing them too much
    2. cooking them too long time

Vitamin Function Food sources Symptom of deficiency Symptom of excess
Vitamin A
Maintains eye health
Promotes growth and development, maintains healthy bones and teeth
Enhances the protection and regeneration of cells and mucous membrane
Maintains healthy respiratory and intestinal tracts
Maintain healthy hair, nails and skin
Dairy products, cod liver oil, liver, dark green and yellow vegetables and fruits
Night blindness, dry eyes
Dry skin
Stomach discomfort
Poor growth
Weak bones and teeth
Dry, scaly, peeling, and itchy skin, rash
Hair loss
Poor appetite, fatigue
Vomiting, stomach discomfort
Liver injury
Headache, bone pain
Nervousness, irritability
Vitamin D
Helps body absorb and utilize calcium and phosphorus, so as to maintain bones, teeth and brain healthy
Maintains normal calcium level in blood
Egg yolk, liver, cod liver oil, fish. Our skins also produces Vitamin D when exposed to sunlight
Children: rickets
Adults: osteoporosis
Calcified cartilage
High calcium level in the blood causes abnormal heart beat and damage to organs such as kidneys
Vomiting, diarrhea
Sore eyes
Itchy skin
Vitamin E
Maintains normal conditions of cells, and healthy skin and tissues
Protects red blood cells
Enhance immunity
Green leafy vegetables, whole-wheat cereals, nuts, egg yolk
New born infants: haemolytic anaemia
Adults: weakness
Low thyroxine level
Headache, dizziness, fatigue
Stomach discomfort, poor appetite
Vitamin K
Helps blood clotting, prevent over bleeding
Maintains health of the liver
Green leafy vegetables, soya beans. The human body can also produce Vitamin K through germs in the colon
Uncontrol bleeding from wounds due to clotting difficulty
Can lead to liver damage
Folic acid
Helps produce cells and red blood cells
Promotes growth and reproductive functions
Dairy products, liver, whole-wheat cereals, beans, banana
Decreased immunity
Stomach discomfort
Vitamin B1
Helps carbohydrate and protein metabolism, thus enabling the body to get energy from food
Helps maintain normal function of the heart, muscles and digestive system
Promotes growth and development
whole-wheat cereals, fish, meat, various vegetables, beans, yeast
Listlessness, insomnia, vomiting
Nervous system problems, depression
Growth retardation in children
Vitamin B2
Helps in carbohydrate, protein and fat metabolism, enables the body to get energy from food
Maintains healthy mouth, lips, tongue, and eyes
Maintains healthy skin, hair and nails
Dairy products, eggs, meat, green leafy vegetables, liver, whole-wheat cereals, nuts, yeast
Inflammation of the oral cavity, mouth corner and tongue
Itchy, dry and bloodshot eyes
Dry skin
Vitamin B3
Helps in carbohydrate and fat metabolism, enabling the body to get energy from food
Regulates cholesterol level
Maintains healthy skin, mucous membranes, tongue and the digestive system
Dairy products, fish, meat, poultry, vegetables, whole-wheat cereals
Rough and inflamed skin
Stomach discomfort, vomiting
Listlessness, headache, fatigue
Vitamin B6
Helps in protein metabolism
Helps produce red blood cells, hormones, enzymes and antibodies
Helps in transmission of nervous impulse
Dairy products, meat, whole-wheat cereals, green leafy vegetables, fish
Nervousness, insomnia, depression
Muscle cramps
Limb numbness, partial loss of sensation
Vitamin B12
Helps produce red blood cells
Maintains healthy nervous system
Promotes appetite
Helps in protein metabolism
Dairy products, fish, eggs, liver, meat
Slowness in thinking, emotional chaos, poor memory
Weakened sensation
Vitamin C
Helps synthesize collagen; promotes the growth and repair of cells, gum, teeth, blood vessels and bones
Helps healing after operation and injury
Helps calcium and iron absorption
Enhances immunity
Citrus fruits (mandarin, orange, grapefruit, lemon), strawberry, black current, kiwi fruit, tomato, green leafy vegetables, green pepper
Gum inflammation and bleeding, fall of teeth
Susceptibility to skin bleeding, burst of capillary vessels
Weakness, fatigue
Bone pain, swollen and aching joints
Abdominal pain
Kidney stone

Should we take vitamin supplements?

There are various kinds of vitamin supplements available on the market. Should we take these "tonics" to maintain good health?
We should maintain a balanced diet and should not be food picky. Healthy eating food pyramid provides general guideline for healthy eating and you will absorb sufficient and appropriate vitamins from your daily intake. There is no need to take extra nutritional supplements to stay healthy.
If you need to have diet control because of any diseases, you should consult a doctor or dietitian. Never take any vitamin pill or supplement on your own.

(Revised in August 2014)
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Last Revision Date : 26 May 2015