What Your Daily Dose of Coffee Does to Your Body

Can't wake up without your morning cup of joe? Find out how that hit of caffeine works its magic—and what happens when you get too much of a good thing.

Caffeine is the world’s most popular drug, regularly consumed by hundreds of millions of adults each day in coffee, tea, soft drinks and energy drinks. Most of us need it to get the day started. Without it we feel foggy and sluggish; too much, and we may turn jittery and get nauseous. But nailing the just-right amount makes us pleasantly alert and productive, even slightly euphoric. We’re all addicted, but is that such a bad thing?

For most of us, it’s not. Caffeine is a central nervous system stimulant that relieves fatigue and improves mood, concentration and focus. For some sporty types, it can boost endurance. Health organizations worldwide suggest that most people can safely consume up to 400 milligrams of it a day—roughly the amount in 33 ounces of brewed coffee or 68 ounces of black tea.

Consuming 600 mg or more a day is when things can, quite literally, get shaky: at that volume, some people experience tremors, increased blood pressure, an upset stomach, headaches, dizziness, heart palpitations and insomnia. Then again, some people don’t. Response to caffeine varies from person to person and is likely determined by two main genetic factors: how quickly your liver can metabolize caffeine and whether your central nervous system is more sensitive to stimulatory effects.

While daily consumption of caffeine doesn’t usually disrupt the heart’s rhythm enough to create dangerous irregular patterns, high doses can temporarily raise your heart rate and blood pressure—a danger for people with heart disease. In rare cases, excess caffeine intake has caused seizures and even death, though mostly among people consuming energy drinks.

Some research suggests that caffeine may protect against dementia, including Alzheimer’s disease. One observational study in The Journals of Gerontology: Series A found that women aged 65 and older who consumed an average of 261 mg of caffeine (two to three cups of coffee) a day for 10 years reported fewer dementia symptoms than women who had consumed an average of 64 mg daily. This effect isn’t yet fully understood, and it’s not known whether it’s the caffeine—or other substances in coffee, such as antioxidants—that is the cause. (Learn how to spot the early signs of dementia.)

In addition to beverages, caffeine is often an ingredient in slim-down supplements because it may briefly reduce feelings of hunger, but there’s no solid evidence that consuming it leads to weight loss. “It’s more important to think about how you take your coffee,” says Dr. Duane Mellor, a registered dietitian and a senior teaching fellow at the Aston Medical School in Birmingham, England. “If it’s black or with a little bit of milk, that’s not a problem. But if you take it with a lot of milk or cream, sugar or syrups, it’s now a high-energy, high-fat drink.” And that, he says, can be more problematic for your overall health than the shot or two of espresso. (Check out these alternative coffee sweeteners.)

For most people, caffeine’s biggest drawback is that it can interfere with sleep, especially the deep “slow-wave” rest that’s vital for the brain and body to recuperate. Worst case, sleep deprivation is associated with obesity and other chronic diseases like Type 2 diabetes and depression. “If caffeine is disrupting your sleep, limit it or cut it out. It’s a no-brainer,” says Mellor.

If you do choose to quit caffeine, Mellor warns, an abrupt decrease in your consumption may cause headaches, irritability, difficulty focusing on tasks and other withdrawal symptoms. Take a breath and cut back slowly.

Next, find out how to make your coffee habit healthier.

Reader's Digest Canada
Originally Published in Reader's Digest Canada