How many of us poured a glass of wine or a stiff gin last night without wondering, if only briefly, whether we might be courting breast cancer?

If there is a sudden dip in the profits of the drinks industry when they come to look back at November 2002, it might well prove to be the result of the massive epidemiological study, coordinated by Oxford University and published this week, which established officially what has often been suspected, that alcohol can play a part in the disease women fear more than any other - breast cancer. There will undoubtedly be women who turned teetotal instantly.

Others will react with anger and dismay at the injustice of it all. Just when it looked as though a quiet drink was an acceptable way to unwind, when there's talk of alcohol helping to prevent heart disease, when government guidelines actually endorse a couple of drinks a night and when we're heading for Christmas, they hit us with this. Is there no innocent pleasure to be had in life? Much of what we eat is bad for us, smoking is lethal (even if it doesn't cause breast cancer), flying gives us deep vein thrombosis and now a drink a day increases the breast cancer rate by 6%.

But hold on a minute, because life - as ever - is more complicated than bald statistics. The only way to make sense of this story and many other health scares is by taking a more sophisticated perspective on it than tabloid headlines allow. It's called understanding risk.

The way the story has been presented suggests that some journalists haven't understood the risk concept themselves. Some television reports stated that a woman's chances of getting breast cancer increase by 6% for every drink she takes. If that were true, all we moderate tipplers would be headed for the cancer ward.

No. The study found that a woman who is in the habit of drinking one unit (small glass of wine/half pint of beer or one measure of spirits) every night has an increased risk of 6% (or 7% if her winebar stocks larger American-style glasses). That's not a figure that rises as time goes on. It's static. If she drinks on average two glasses a night, the increase is 12%, and so on. This is an increased risk on top of the risk women run before they ever touch a drop.

But to get any real idea of a woman's chances of getting cancer, you must look at what her risk was to begin with. The risk over a woman's lifetime is one in nine - but it is heavily weighted towards old age. The risk up to the age of 30 is one in 1,900,up to 40 is one in 200 and up to 50 is one in 50. So it follows that by the time she is 40 a woman has a risk of 0.5%, which becomes around 0.53% if she drinks a glass a night. By the time she is 80, her 8.8% risk has risen to around 9.4%. If she drinks two vodkas a day, it is 10.1%. If she drinks three gins it is 10.8%, and so on.

If doesn't take a mathematical genius to work out that it's a very small increased risk. Since young women have a much smaller risk to start with - although that can be raised if breast cancer runs in the family - a couple of drinks a night more or less is hardly going to make any difference at all. Ironically, for older women, the protective effect of alcohol against heart attacks starts to kick in at the mid-60s, and becomes a much greater cause of death than breast cancer. A couple of gins a night at that stage of life starts to look like a good idea.

To give the scientists their due, they were not angling for scary headlines at their press conference on Tuesday. Sir Richard Doll, the wonderful 90-year-old veteran epidemiologist famous for proving that smoking causes cancer half a century ago, was asked who should be concerned by the findings. "I think nobody should be worried," he beamed. "People that drink more than four units of alcohol a day are probably not doing themselves good for a lot of reasons... but we don't want to discourage people from having one or two drinks a day if they enjoy it."

There are more important issues around alcohol. Young women are drinking harder than ever before, matching the macho in the bar even though their constitution is ill set-up to deal with it. Yet there is still some shame in admitting how much you drink. In the studies, the average professional woman claimed to have 8.6 drinks a week. Really? We should come cleaner about our drinking habits and the impact of them on our relationships and especially on our children. Alcohol is also responsible for a vast amount of violent crime. But what we don't need is to shake with fear as the glass touches our lips at the thought of cancerous cells starting to divide in our bosoms.