Drugs can prevent disease as well as cure it. Should we be loading up on pharmaceuticals to stay healthy?

What would you say if you heard that drugs were being pumped into the water supply? Would it horrify you? In fact, it has been going on for decades, with fluoride. Six million people in the UK currently drink tap water spiked with fluoride.

When fluoridation began in 1945 it was hailed as a harmless chemical to prevent tooth decay. But the practice has had its critics, who claim fluoride can cause a range of health problems - from tooth mottling to cancer (the evidence for which is not strong).

The Government backs water fluoridation as a cost-effective way to tackle tooth decay, insisting that there is no evidence to suggest it is dangerous and plenty of evidence that it reduces tooth decay. However, some people feel it should be a matter of choice. Fluoride can also be obtained easily from toothpaste.

Plans to make people eat folic acid by adding it to bread have also ignited controversy. The UK's food watchdog, the Food Standards Agency, recently proposed that all white flour be fortified with extra folic acid, a synthetic form of vitamin B9, to reduce the number of babies born with spina bifida. It is now up to ministers to decide whether to go ahead with the proposal.

Folate is found in many foods, particularly green vegetables. Experts agree, however, that diet is unlikely to provide enough of this vitamin. So currently all mothers-to-be are urged to take folic acid supplements. Babies born with spina bifida grow to adulthood with paralysis and bowel and bladder incontinence.

Compulsory fortification already happens in the USA, Canada and Chile, and the number of neural tube defects such as spina bifida has been cut by between 27 and 50 per cent. In the UK, around 200 babies each year are born with neural tube defects - which could be avoided, some experts say, if folic acid were added to bread.

But some consumers argue that compulsory fortification of all flour restricts their choice. There are health issues too, as some research suggests that over-consumption of folic acid may increase the risk of bowel cancer and, in elderly people, lead to brittle bones.

If a wonder pill existed that could prevent society's number one killers - heart attack and stroke - should all adults be taking it? Controversy flared in 2003 when two British doctors proposed the idea of a polypill - a mix of aspirin (to prevent blood clots), a statin (to lower cholesterol) and two blood-pressure lowering agents. They argued that, taken daily by all people aged over 55, this polypill could slash heart attacks and strokes by more than 80 per cent.

Hold on, said critics - such a pill would medicalise life and undermine an individual's responsibility to keep fit. Dutch scientists came up with an alternative. Forget the pills, they said, and dine regularly on the 'polymeal': fish, garlic, almonds, fruits and vegetables, dark chocolate and wine. These natural alternatives could cut heart diseases. And would be more enjoyable too.

Joking aside, there is a growing emphasis on disease prevention. Is there any reason pharmaceuticals should not be part of the way we stay fit and healthy?