A: Coffee is the most concentrated source of caffeine in our diets, with each mug giving you about 100 milligrams. This caffeine can interfere with the absorption of certain minerals, including magnesium, calcium, and iron, but the loss is minimal. And while some studies suggest that drinking coffee can thin bones, you can offset the danger by adding milk. (I recommend nonfat powdered milk, which delivers calcium but adds few calories.)
Recent research shows that if anything, coffee contributes nutrients to your daily intake. It's the leading source of antioxidants in the American diet—not because it contains more than antioxidant-rich red wine, dark chocolate, and tea, but because we drink so much of it. Though most people believe they should cut back, research suggests that drinking up to three cups a day can actually have beneficial effects on health. And you can offset any mineral loss by eating plenty of fruits and vegetables and taking a daily multivitamin and mineral supplement.
As for alcohol, it will hamper absorption of folate and thiamin, two essential B vitamins. But with moderate drinking—not more than one drink a day for women, two for men—these effects are modest. (One drink is 12 ounces of beer, five ounces of wine, or one and a half ounces of spirits.) Like coffee, alcohol in moderation may offer certain health benefits, such as reduced risk of cardiovascular disease. Alcohol does carry more potential dangers, though: It may increase risk for several cancers, including breast cancer, and there's always the specter of alcoholism. In the big picture, it's not a glass of wine or a cup of coffee but your overall diet that's important. As long as you eat healthfully, there's room for both beverages if your tastes, like mine, are so inclined.