The beverage, which is best known for keeping people alert and sobering up drunks, has caused a stir by suggesting women who drink more than three cups a day could see their bra size drop.
Tests by cancer researchers found half of all women have a gene linking breast size to coffee intake.
Nearly 300 women were quizzed but Helena Jernstroem, of Lund University, said women should not worry too much.
"Coffee-drinking women do not have to worry their breasts will shrink to nothing overnight. They will get smaller, but the breasts aren't just going to disappear," the Daily Star quoted her, as saying.
"Anyone who thinks they can tell which women are coffee drinkers just from their bra measurements will be disappointed.
"There are two measurements for a bra - the cup size and the girth, so you wouldn't be able to tell," she added.
While caffeine may shrink women's breasts, the reaction is the reverse for coffee-slurping blokes - it can make their "moobs" swell.
On the plus side, the study showed regular hits of caffeine reduce the risk of women developing breast cancer.