Is caffeine part of your everyday routine? Maybe you rely on it to get through that afternoon slump or a night shift at work.

It’s estimated that 90% of U.S. adults ingest some form of caffeine every day, and for most it’s in the form of coffee or espresso drinks. While caffeine often gets a bad rap, recent studies suggest that it improves your mood and may help you live longer, as long as you aren’t guzzling the stuff.

So how much is too much?

One study by Dr. Greg Marcus, a professor of medicine in San Francisco, suggests that coffee is not detrimental to our health and that regular coffee drinkers are at lower risk of diabetes, Parkinson’s disease and some types of cancers.

According to the Food and Drug Administration, the recommended caffeine intake is no more than 400mg per day. This is equivalent to five cups of coffee.

For tea enthusiasts, an 8-ounce cup of tea contains 30-50mg of caffeine. Energy drinks, on the other hand, may have up to 250mg. On average, a 12-ounce bottle of caffeinated soda may contain up to 40mg.

If you drink caffeine in moderation, you’ll feel more alert and improve your energy levels.

What happens when you drink too much caffeine?

If you drink more than 12 cups of coffee in a day, it could raise your blood pressure or make you feel anxious. Some folks have trouble sleeping, too.

Also, if you drink multiple cups a day, stopping suddenly can lead to withdrawal symptoms like headache and fatigue.

How can you know you’ve taken too much? The effects of caffeine vary from one person to another. People have different metabolisms, and a moderate amount of coffee for you may be enough to keep someone else up all night.

Other factors for how it might affect you include body weight and medications you may be taking.  

In a randomized study, Dr. Marcus asked the participants to stop drinking coffee for two days, drink for the next two days, and then repeat the regimen over a two-week period.

Although the findings were preliminary, people were more active on the days they drank coffee than on those days they went without. He further observed that the subjects had no abnormal rapid heartbeats in the lower chambers of the heart.

In his cardiology practice, the professor tells patients with abnormal heart rhythms to experiment by taking coffee.

While he espouses drinking coffee, Dr. Marcus advises against drinking energy or other artificially caffeinated beverages, as they can sometimes cause blood pressure to spike or result in abnormal electrical activity in the heart.

What are the best ways to stay alert?

If you want to stay alert without compromising your health, the secret is adopting a healthy routine. You should exercise regularly and ensure you get a good night’s sleep.

Dr. Marcus advises those with an irregular sleep-wake cycle to consult their physician to see if they have a sleep disorder.