It's the moment you dread when you go for a medical - when you're asked about your alcohol consumption. I was seeing a cardiologist, having been diagnosed with angina - ironically after years of a health-conscious diet low in saturated fat, reasonable fitness and never having smoked. "How much do you drink?" she asked. Sheepishly, I suggested maybe a glass or two of wine or beer most nights.
"You need to drink red wine, not white or rosé. One glass a day isn't enough; two's better, preferably three," came the reply. "It's very good for your blood vessels."
The instruction was almost as much of a shock as the onset of my angina, the chest pain that occurs when your heart muscle isn't getting enough oxygen because of reduced blood flow caused by blockages (atheroma) in the arteries.
Drinking three glasses of red wine daily, much of which contains up to 15% alcohol, is well over the British Heart Foundation's (BHF) recommended drinking limits. These are based on three to four units of alcohol a day for a man (two to three for a woman) where each unit is 125ml - a small glass - of 8% strength wine. These days, it's much easier to find a beer at that strength than such a weak wine.
The health virtues of a Mediterranean-style diet with plenty of fruit and veg, oily fish and olive oil, washed down with red wine, are well known. But is the wine really significant?
Drunk in moderation, and preferably with food so that the alcohol absorption is slowed, all the population studies indicate that it is. But drink it in excess and, as recent studies on the dangers of hazardous drinking testify, it will do you much more harm than good.
Several studies are summarised in a book called The Wine Diet by Roger Corder, professor of experimental therapeutics at the William Harvey Research Institute in London. He cites, for instance, a Californian study published in 2003. It followed nearly 130,000 people over 20 years and found that those who drank a glass or two a day had a lower death rate from any cause and 60% fewer coronary heart disease deaths.
The reason is polyphenols, a cocktail of thousands of chemicals that occur naturally in red wine and contribute to its colour, taste and, in some, its harsh astringency. Many are found in the skin and around the pips of red grapes. Some come from wood when the wine is aged in oak barrels. White wine, however, contains no polyphenols. And because the juice for making rosé is separated from the pips and skins before fermentation, it has next to none either. Nor do beer or spirits.
Most polyphenols aren't soluble in grape juice (so there's no benefit to the arteries from drinking it), but as the alcohol concentration increases during wine fermentation, they dissolve into it.
Unfortunately, not all red wines are equally rich sources of these chemicals. Grape variety, winemaking style, soil type - and perhaps other factors - all make a difference. Corder has analysed many and has found that red wines using Tannat or Malbec grapes usually contain the biggest doses.
The wine with the highest known polyphenol levels is Madiran - made from Tannat in southwest France - a tough, heavy, inky red bruiser of a wine not often seen outside France. According to Corder, one small glass of it has more polyphenols than two bottles of most Australian reds. Many of the big-brand Aussies, while overly rich in alcohol, are generally poor for polyphenols - though some of their cabernet sauvignon-based wines are better.
Better are some Argentinian reds: Malbec is commonly grown in Argentina and is also the grape of Cahors, from south-west France, another heavy blusterer of a wine, dark, dense and tannic. The Tannat grape, in addition to fuelling Madiran, is also the grape used to make many of the sturdy, plummy - and cheaper - wines of Uruguay.
South-west France stands out as the place to be if you want to live a long life. In spite of a diet rich in saturated fats from foie gras, cassoulet and copious cheeses, parts of this region have double the French average of men aged 90-plus. Corder puts it down to the local red wines, exemplified by the gutsy Madiran.
No one is yet sure how polyphenols help to protect arteries against disease. Nor how much you need to consume to do so. Corder thinks that they might bind to a surface protein on artery walls and help smooth the flow of blood, a bit like creating a non-stick surface. This helps prevent the build-up of atheroma - the accumulations of blood cell debris, cholesterol, calcium and other substances - which eventually causes constrictions to blood flow and leads to angina and heart attacks.
Several other foods and drinks are rich sources of polyphenols, too. If you enjoy other sorts of tipple, try cider, but only the cloudy, unfiltered kind as filtration removes all the polyphenols.
So why doesn't the BHF promote a sensible intake of polyphenol-rich red wine to accompany its advice on eating plenty of fruit and veg, taking exercise and, of course, not smoking? Its website refers to "drinking alcohol in moderation" without mentioning red wine at all. Nor does it have any guidance about polyphenol-rich foods.
Professor Jeremy Pearson, associate director of the BHF, admits that there is convincing evidence of the virtues of red wine. "Maybe it's time we revised our policy," he says. "I think that perhaps we are being too cautious. We've always been reluctant to promote alcohol because of the obvious risks of over-drinking, but I think there's enough evidence now for us to have a re-think".
If you are not a drinker, other sources of polyphenols include dark chocolate, walnuts and cranberries. Or as the adage almost goes, an apple a day keeps the cardiologist away.
