For 63 percent of Americans this year, coffee is a daily essential. This number has been this high since 2017, according to the National Coffee Association. The rise of coffee is due to its numerous benefits, liking preventing DNA damage, but it works best if you do this simple thing: eat.

“Drinking coffee on an empty stomach, or early in the morning before you’ve had breakfast, can increase the level of cortisol in your body. From the moment you open your eyes in the morning, your body starts releasing cortisol, a hormone that’s responsible for regulating your immune response, metabolism, [and] stress response,” says Dr. Nikola Djordjevic, MD.

If you pump your body with caffeine when your cortisol is at its peak, Djordjevic says, you’ll be subjecting your body to even more stress. In a pilot study that evaluated preferences of caffeinated drinks among medical students, it showed that 25 percent of students drank coffee in the morning on an empty stomach. They should try brewing a cup of joe at the best time of day to drink coffee, instead.

These students are at an increased risk of mood changes and possible long-term impacts to their health, as explained in the study. This is because coffee stimulates the acid in your belly, producing a more acidic environment.

“Coffee on an empty stomach can magnify the stimulating effects because there is nothing to compete with absorption,” says Dr. Jamie Long, licensed clinical psychologist. Thus, a full belly is vital to curb the amount of stomach acid produced.

Since coffee irritates your stomach acid, you’re highly likely to experience heartburn and even develop gastric ulcers, Djordjevic says. Clearly, coffee on an empty stomach affects physical health. But it ropes in mental health, too. The overproduction of acid in the stomach can cause mood swings, jitters, shaking, and other withdrawal symptoms, Djordjevic says. In addition, there have been studies that link gastric acid to anxiety and depression, she explained.

“Especially when consumed in large amounts, studies have found that caffeine mimics symptoms of anxiety and even panic attacks. Symptoms can include restlessness, trembling, flushed face, and accelerated heart rate,” Long says. “And if you’re already prone to experiencing anxiety, you’re even more vulnerable to the effects of coffee.”