A study from the Wake Forest University School of Medicine found an amount of caffeine equal to what's in two to three cups of coffee can constrict blood vessels and reduce cerebral blood flow. The report appears in the April issue of Radiology.
Heavy caffeine users had more blood flow to the brain when they were in a state of caffeine withdrawal, the study also found. That indicates a direct correlation between the amount of regular caffeine consumption and blood flow measurements.
"The more caffeine you drink on a regular basis, the higher your cerebral blood flow will be when you do not consume caffeine," study author Dr. Aaron S. Field says in a news release.
The study used fMRI to examine the effects of caffeine consumption and withdrawal on the cerebral blood flow in 20 healthy adults. Half of the people in the study were put into a low caffeine consumption group, and the others were ranked as heavy caffeine users.
Daily caffeine consumption in the United States is a bit more than two cups of coffee per person. That equals 238 milligrams.
The people in the study were scanned with fMRI at about the same time of day on two different days. They were randomly chosen to take a placebo on one day and a 250 milligram dose of caffeine on the other day about 90 minutes before being scanned.
To induce caffeine withdrawal, they had to abstain from caffeine for at least 30 hours before being tested.
Caffeine reduced cerebral blood flow in gray matter areas of the brain by about 23 percent in all the people. The blood flow in the gray matter of heavy caffeine users was reduced by 26 percent and by 19 percent in light caffeine users.
During withdrawal, the blood blow in the heavy caffeine users was more than 30 percent greater than in the light caffeine users experiencing withdrawal.
"Dramatic differences in cerebral blood flow measurement can be seen from one day to the next based on a single cup of coffee. This shows researchers the need to control for caffeine effects," Field says in the news release.
Here's where you can learn more about caffeine.