About 300 healthy pre-menopausal non-hormone using women were questioned about their coffee intake and had their bust measured. It was found that the women who drank 3+ cups of coffee a day had ~17% smaller breasts than those that drank less. However, this relationship was found only in women that were carriers of a specific genetic variant. The good news for these women is that previous studies have shown that coffee may protect carriers of this same genetic variant against breast cancer. About half the women in this study were carriers of this gene.
Lead author Helena Jernstrom stated that although “Drinking coffee can have a major effect on breast size...coffee-drinking women don’t have to worry ... breasts aren’t just going to disappear.”Health Canada recommends you not exceed 400mg caffeine a day. Women in their childbearing years should not consume more than 300mg. A generically brewed cup of coffee has between 100-200 mg caffeine.