It’s a hot summer afternoon, and the benches outside my local Starbucks are packed with people who share the craving that brought me here: iced coffee. I prefer my coffee hot, but in July, adding ice turns it into the perfect summer refreshment.
Still, the more I drink—and I do drink a lot—the more the caffeine gets my mind racing and thinking about the wisdom of my habit. I know what my iced coffee is doing for me, but what’s it doing to me? I’ve heard that it’s dehydrating, for example, which is hardly a good thing, particularly in the heat of summer. And what about the articles I’ve seen that say coffee raises the risk of heart disease and cancer?
Fortunately, the answers to these questions turn out to contain some pleasant surprises. It’s true that the caffeine in coffee (and in tea, colas, and to a lesser extent, chocolate) is possibly the world’s most frequently used drug. But recent research suggests that for those of us who drink no more than a cup or two a day, the good news about its health profile outweighs the bad.
Perks and pitfalls
First, about that dehydrating effect. Coffee does have some diuretic properties, which is why people say it doesn’t count as one of the eight glasses of water we’re all supposed to drink in a day. But in a recent report, the Institute of Medicine at the National Institutes of Health concluded that caffeine’s diuretic effect is fleeting and does not contribute to significant fluid loss. Of course, eight cups of espresso might indeed make you feel a bit shriveled. But the occasional cup shouldn’t have that effect—and can even count toward your daily eight.
The main benefit of coffee—no surprise—is the buzz that gets us up in the morning, keeps us alert while driving, and prevents us from nodding off in boring meetings.
But there’s more: Despite periodic warnings that coffee raises our risk of cancer and heart disease, the weight of the evidence shows that it’s been falsely accused. As part of the ongoing Nurses Health Study at Harvard, researchers followed 85,700 female nurses for ten years and found that coffee played no role in their heart health. And in similar studies, Italian, Spanish, and U.S. researchers have concluded that coffee does not significantly contribute to cancers of the breast, bladder, or pancreas.
It does reduce the risk of gallstones, however, which afflict 20 million Americans, and evidence is mounting that moderate consumption—about one to three cups a day—helps protect against Parkinson’s disease. There’s even good news for the most dedicated java junkie: Drinking lots of coffee reduces the odds of Type 2 diabetes, which is all too common and, as a major risk factor for heart disease, very deadly.
In a recent Harvard study that looked at 126,000 men and women for up to 18 years, men who drank six cups or more a day saw a 54 percent decrease in their risk of developing diabetes; women’s risk dropped by 29 percent. Of course, if I drank enough coffee to make my diabetes risk plummet, I’d be so wired I’d never fall asleep. And there are healthier ways to prevent diabetes than overdosing on coffee (weight control, exercise, and diet, to name a few). But the study showed that even a daily cup or two may help a little.
With all these benefits, you might be tempted to call coffee a health drink. Not so fast. Everyone knows that for some people, even a small amount of caffeine can cause insomnia, jitters, and crankiness. And some evidence suggests that coffee raises fluid pressure in the eye, which may contribute to glaucoma. Its biggest downside, though, may be its effect on a woman’s fertility.
Studies suggest that drinking more than three cups a day can make it harder for women to get pregnant. (Men hoping to become fathers might have an extra cup, however. Some studies suggest that caffeine boosts the motility of sperm.) In one study of 1,500 women, Danish researchers discovered that those who miscarried were more than twice as likely to report drinking more than 375 milligrams of caffeine a day. (Caffeine amounts vary widely, even within the same brand, but 375 mg is approximately what’s in three or four cups of coffee.) And some research suggests that pregnant women who drink more than three cups a day have an unusually high rate of spontaneous abortion. Robert Barbieri, chief of obstetrics and gynecology at Brigham and Women’s Hospital in Boston, advises pregnant women and those trying to conceive to limit their caffeine intake to no more than 250 mg a day, or two and a half cups.
As for everyone else, the message seems pretty clear: Coffee’s no fresh-squeezed orange juice, but it’s no sugary cola, either. Unless you’re looking to justify a long-standing habit as a way to prevent diabetes, the best approach is the one that holds for most things in life: moderation.