Too much of a good thing?

PUBLISHED : Sunday, 12 September, 2010, 12:00am
UPDATED : Sunday, 12 September, 2010, 12:00am

Yin-yung asks: Is it necessary to take vitamin capsules?

Wynnie says: Sales of nutritional supplements are at an all-time high. Many people swallow them by the handful, at great expense, to ward off a variety of illnesses and ailments. But do vitamin pills really do us any good, or are they actually harmful?

Why do we need vitamins?

Vitamins are nutrients that fuel essential processes carried out in the body. But we usually only need a few milligrams or even micrograms of each vitamin a day. Most vitamins can't be manufactured by the body, so must come from our food. Vitamin D, however, can be made by the body via the action of sunlight on the skin. And niacin (vitamin B3) can be made from an amino acid called tryptophan.

Vitamins have many functions in the body: some help enzymes to function, some are antioxidants, preventing oxygen from damaging the body, and some act like hormones. If we don't get enough vitamins because we don't eat well, or because we are sick, than symptoms will appear that can develop into a deficiency disease. Vitamin deficiency diseases, however, are rare in westernised places such as Hong Kong but occur in many other parts of the world.

For most of us, a balanced and varied diet provides us with all the vitamins and nutrients we need. A balanced diet includes foods from four main food groups - bread, potatoes and other cereals; fruits and vegetables; lean meat, fish, pulses and nuts; and low-fat dairy products.

However, some people may actually need supplements, such as the elderly, pregnant and breastfeeding women and strict vegans.

How much is too much?

Although a little is good, a lot may not be better. For example, fat-soluble vitamins such as vitamins A and D are stored in the body, so taking large amounts over a long period of long time can be toxic.

Too much vitamin D can cause liver damage, and excess vitamin A can cause liver and bone damage, hair loss, double vision, vomiting and headaches. Even excess water-soluble vitamins can cause problems if taken over prolonged periods for example, high doses of vitamin C can cause diarrhoea, kidney stones and bladder problems.

A recent study of 232,000 people compared those taking beta carotene, vitamins A, C, E and selenium supplements with those taking a placebo. Researchers found no evidence that the supplements prolong life.

So how much is enough?

The American Dietetic Association says those already eating a healthy diet will only ever need low doses of supplements. Taking a multivitamin with no more than 100 per cent of the 'daily values' as a safety net is generally considered safe.

Bottom line: Vitamin and mineral supplements are no substitute for a varied, balanced diet. You can't make up for a poor lifestyle by popping pills. If you do decide to take supplements, ask a doctor first.

Yin-yung's diary

Breakfast: Bread and fruit

Lunch: Rice, vegetables, meat and fish

Dinner: Rice, vegetables, meat and fish

Snacks: Biscuits occasionally

Exercise: Two hours of badminton once a month, 1 hour running once a week