According to a 2014 study, 85 percent of the U.S. population consumes at least one caffeinated beverage per day, with coffee as the leading source by far, for an average intake of 165 mg per day across all age groups. People ages 50 to 64 are the biggest caffeine consumers, with an average 226 mg per day.
That is a very large group of people ingesting "the most widely consumed psychoactive substance in the world," as UAB researchers described caffeine in an article published last month in the journal Psychopharmacology. So, naturally, scientists have lots of questions about what caffeine does for people.
The Mayo Clinic notes that consuming up to 400 milligrams of caffeine per day, which is equivalent to roughly four cups of coffee, appears to be safe, although children and women who are pregnant or are breastfeeding are urged to limit caffeine use.
A team led by UAB graduate student Demario Overstreet and Burel Goodin, PhD, an associate professor in the UAB College of Arts and Sciences Department of Psychology, with a research focus on pain modulation, wondered whether a person's daily intake of caffeine had an effect on their sensitivity to pain. Caffeine is already used in acute pain treatments (and it is an ingredient in some headache medicines). But does higher caffeine consumption in the diet make people experience less pain?
To find out, the researchers recruited 62 participants ages 19 to 77 and asked them to record their daily caffeine consumption for seven days. The average was 170.8 milligrams per day, while the highest was 643.6 milligrams per day, or roughly 6.5 cups of brewed java -- well above the "safe" recommended maximum.
Researchers then put the participants through a series of uncomfortable tests using heat and pressure, recording how long they tolerated the pain before pressing a button to end the trial. The result, according to their paper: "greater self-reported daily caffeine consumption was significantly associated with higher heat pain threshold, higher heat pain tolerance and higher pressure-pain threshold." Each additional 100mg of daily caffeine consumed, for example, was associated with a 0.5 degree Celsius (0.9 degrees Fahrenheit) increase in heat pain threshold.
Previous studies have shown that caffeine blocks receptors for the neurotransmitter adenosine, which interferes with pain-signaling. This study "provides l evidence suggesting that greater levels of habitual dietary caffeine consumption may alter the nociceptive [related to the body's primary pain receptors] processing of pain signals," the authors wrote.
New research shows that, irrespective of weight loss, a proper diet can decrease the severity of pain, Goodin says. But this message is not widely understood, he added: "People just don't realize that their diet, including caffeine consumption, can be used as a pain intervention."