That’s the good news. And now the bad. A study published earlier this year demonstrated that pregnant women who consume 200 milligrams of caffeine or more per day (that’s less than one Tall Starbucks drip coffee or three six-ounce cups of traditional coffee) are more than twice as likely to have a miscarriage as those who don’t use any. Too much caffeine during gestation may also contribute to low birth weights in children and result in babies born with a caffeine dependence. Large daily doses may also be a factor in female infertility. A study released in late May found that drinking coffee before breakfast could cause blood-glucose levels to rise sharply, which can be dangerous for people with type 2 diabetes. Drinking large amounts of caffeine has been found to exacerbate osteoporosis. And despite the popular idea that caffeine can relieve migraines, doctors say it more often causes them (Caffeine withdrawal seems to be the trigger). “Starbucks has been a big boon to our business,” says Alexander Mauskop, director of the New York Headache Center.
The most serious negative effects of hypercaffeination involve stress and sleeplessness. Because the drug is linked to the production of adrenaline and cortisol, hormones which are in turn associated with the fight-or-flight response, says Duke’s James Lane, “for someone with a busy, stressful job, little stresses elicit big responses on caffeine, and big stresses elicit huge responses.” Lane once did a study in which he compared caffeine’s effects on type-A versus type-B personalities. “Caffeine tended to make type Bs into type As,” he says. “Their blood pressure went up. They rose to challenges.” The type As didn’t get any more ambitious; they just became more excitable. Stress has been linked to everything from cancer to sexual dysfunction to depression. Before she prescribes an antianxiety drug like Xanax, Juliano advises her patients to quit coffee.
Caffeine’s ability to delay the onset of sleep is, of course, one of its chief selling points. But while caffeine can keep us awake, says Lane, “it doesn’t make the brain any less tired.” That’s why it’s possible to lie awake at 3 a.m. clicking through infomercials but still feel mentally exhausted. Depending on one’s caffeine metabolism, just one strong cup of morning coffee can be enough to disrupt sleep at night; an afternoon recharge is that much more likely to do so. “We routinely ask patients who are insomniacs to discontinue the use of caffeine, or reduce it to a cup or two in the morning,” says Charles Pollak, director of the Center for Sleep Medicine at the New York Weill-Cornell Medical Center. “And no caffeine after noon.” The United States Centers for Disease Control reports that sleep disorders are more pervasive than ever. Americans, on average, are getting 6.7 hours of sleep per night, the lowest amount since records have been kept, and are racking up an hour or more of sleep deficit per day. Sales of Ambien, Lunesta, and other prescription sleep aids have more than doubled in the past few years. “You have people drinking caffeine all day and taking sleeping pills at night,” Juliano says.
The effects of sleep deprivation are wide-ranging. The body’s ability to fight off disease is weakened. The body produces less leptin, a hormone that regulates appetite, leaving a sufferer hungrier than she would normally be. For that reason, sleep loss is increasingly seen as a major factor in the obesity epidemic. The sleep-deprived are more susceptible to depression and tend to have less control over their emotions. Sleep loss also weakens problem-solving and decision-making skills and, naturally, leaves a sufferer exhausted—all of which are conditions that caffeine is called upon to solve. “If we drink coffee all day long, it’s harder to sleep at night, and we need more coffee to get up and go to work the next morning,” says Lane. “The cycle repeats itself.”
No one can say for sure how much caffeine is safe, but just about everyone preaches moderation, and 300 milligrams seems to be the upper limit of what’s considered a moderate daily intake. That translates to about one Starbucks Grande drip coffee, four and a half six-ounce cups of traditional coffee, eight and a half twelve-ounce Cokes, or six eight-ounce cups of tea. Doctors note that pregnant women and nursing mothers and those who suffer from any of the health problems associated with caffeine would probably do well to drink little or none of the stuff.