What really makes you live longer. Aspirin, vitamins or cod liver oil?

The news last week that taking low-dose aspirin could cut your risk of cancer by a quarter will send plenty of us rushing to the chemist. Indeed, we are rapidly entering an era where everyone is taking preventative drugs. For drug companies, the potential profits from preventative pills are huge; healthy people make far more sustainable customers than seriously ill ones.

But these pills have side-effects, and some of these can be serious. It is up to each of us to weigh up the risks and benefits.

ASPIRIN

A recent study revealed that a 75mg aspirin tablet a day substantially cuts death rates from common cancers. The Lancet study found that people taking it had a 25pc lower risk of death from cancer and a 10pc reduction in death from any cause, compared with patients who were not given the drug.

Aspirin is already known to cut the risk of heart attack and stroke among those at increased risk. Professor Peter Rothwell, the lead researcher, is not urging healthy middle-aged adults to start taking aspirin immediately. His reticence is due to aspirin's main side-effect, stomach bleeding.

A study last year found that daily aspirin can increase the risk of dangerous internal bleeding by a third. It can also cause haemorrhagic strokes. The complication rate means that if aspirin were submitted today as a new drug to clinical trials, it would fail.

COD LIVER OIL

Cod liver oil has been revived in the past decade as a one-a-day wonder for healthy hearts, supple joints and sparky brains. It's been said that if you want luscious locks, like Scarlett Johansson, who is poster girl for L’Oreal haircare products, then cod liver oil should be top of your shopping list.

Also, critics have suggested recently that there is a dearth of large-scale study evidence to support its wonder qualities.

In September, doctors studied nearly 7,000 people with chronic heart failure and found that 1g of fish oil capsules a day cut the death rate by 9pc. Hospital admissions also fell. A recent study by the University of California may help to explain why: omega-3 fatty acids in the oil switch on receptors in blood that prevent harmful inflammation in the heart and arteries.

There are, however, worries about harmful mercury contamination, particularly for pregnant women.

VITAMINS

There is alarmingly little medical research on vitamins. Most studies say they are of little or no use, especially if you have a normal healthy diet. Some multivitamin supplements might even be dangerous; Swedish researchers warn that an overdose of multivitamins increases the risk of breast cancer.

However, vitamin D shines through. It is essential for healthy bones and to protect against a range of diseases including cancer, heart disease, diabetes and multiple sclerosis.

With most of us leading increasingly indoor lives, increasing numbers of us are becoming deficient.

STATINS

Statins lower cholesterol levels and a Lancet study last year said that daily statins cut the risk of strokes by about a fifth. They have also been shown to prevent arteries ageing prematurely. Statins may also protect against arthritis and help the body to combat serious infections by activating bacteriakilling white blood cells.

They were developed for people with high cholesterol, but drug industry-backed research recently concluded that they lower the death risk for everyone, even those with low cholesterol. One British cardiac consultant even said that they should be put in the water supply.

But statins can have side-effects, including muscle problems, sexual dysfunction, serious depression, sleep disturbance and memory loss. Critics also fear that people wrongfully believe that statins can enable them to carry on overeating and underexercising.

SEX HORMONES

Some studies estimate that hormone replacement therapy (HRT) extends life by three years because it cuts the risk of heart attack in women by 50pc. It also helps to beat osteoporosis. But, in 2001, a large study in America showed that HRT increases the risk of breast cancer.

But it still has its proponents.

Last month researchers reported that HRT can rejuvenate the brains of women in their 50s and 60s. The general expert consensus is that HRT remains an effective short-term treatment for menopausal symptoms.

THE POLYPILL

The idea of a single pill that wraps up the life-saving benefits of several other preventative drugs was mooted in 2003. Now scientists in London are beginning a worldwide trial on it.

The pill contains low-dose aspirin, a statin and two drugs to lower blood pressure. The test will see if it can cut heart attacks and strokes in 2,000 people thought to be at risk.

There is a chance, however, that a polypill might combine all the bad sideeffects with few of the benefits.

HOLY GRAIL

The ultimate goal of researchers is to find a natural substance (after all, aspirin comes from willow bark) that has no side-effects but protects against a primary cause of disease — ageing cells. Scientists thought they had got it in resveratrol, found in grape skins and red wine. Early tests indicated that it may act as a serum of cellular youth, preventing Alzheimer's in mice. GlaxoSmith-Kline bought the patent off its developers, then trialled it on cancer patients. But it caused kidney damage and the trial had to be stopped earlier this year.