MONDAY, Oct. 13 (HealthDay News) -- Drinking coffee or consuming other caffeine-laden foods does not appear to boost breast cancer risk, new research indicates.

Caffeine "does not appear to be associated with overall risk of breast cancer," observed study co-author Dr. Shumin M. Zhang, from the division of preventive medicine, in the department of medicine at Brigham and Women's Hospital and Harvard Medical School in Boston.

"However," cautioned Zhang, "when consuming a high amount of caffeine or four cups or more daily of coffee, there is a possibility of increased risk of breast cancer for women with benign breast disease, or for developing certain subtypes of breast tumors that have less favorable prognoses."

The study, funded by the National Institutes of Health, was published in the Oct. 13 issue of the Archives of Internal Medicine.

The authors noted that caffeine -- found in coffee, chocolate, tea, soft drinks and various medications -- is thought to be the world's most commonly ingested drug.

That said, recent research focused on women diagnosed with non-cancerous breast disease revealed that cutting caffeine from the diet could improve symptoms among such patients. Because benign breast disease is considered to be a risk factor for developing the malignant form of the disease, this finding had raised concerns that caffeine might also elevate the risk for malignant breast cancer.

To explore this possibility, Zhang and colleagues from Tokyo Women's Medical University in Japan looked at the diets of a pool of almost 39,000 women over the age of 45 over a period of four years, between 1992 and 1995. All the women worked as health-care professionals -- three-quarters as registered nurses.

The research team observed that nearly one-quarter never drank coffee, and about another quarter drank either one cup or less per day. Almost a third consumed two to three cups per day, while just over 15 percent downed four or more cups on a daily basis.

Within approximately a decade following the collection of dietary information, almost 1,190 of the women developed invasive breast cancer.

Yet, consuming caffeine in any of its forms was not found to be significantly associated with breast cancer risk.

However, among those with a history of benign breast cancer disease, those consuming caffeine at the highest end of the scale did have a "borderline significantly increased risk" for malignant disease. A similar positive link was found between caffeine consumption and the risk for developing tumors larger than two centimeters. Caffeine raised the risk for such tumors by 79 percent, Zhang and his team found.

As well, the risk for developing certain forms of breast cancer -- known as estrogen and/or progesterone receptor-negative breast cancer -- also rose with caffeine consumption by 68 percent, the researchers noted.

The team pointed out that since such types of breast cancer and/or tumors in excess of two centimeters are associated with poorer outcomes, it's important to continue to investigate whether or not caffeine truly has a negative impact on the ongoing development of specific kinds of breast cancer -- even if the general risk remains insignificant.

Dr. Alan Astrow, director of the division of hematology/oncology at Maimonides Medical Center in New York City, suggested that the findings are both comforting and preliminary.

"Overall, the results of this study should be reassuring to women who are concerned about their risk of breast cancer and who also like to drink coffee moderately," he said. "However, the field of diet and breast cancer risk remains one of active research, and the results of these kinds of investigations are not always easy to interpret. It is possible that future studies will show a different result."

Dr. Larry Norton, deputy physician-in-chief of Breast Cancer Programs at Memorial Sloan-Kettering Cancer Center in New York City, agreed.

The findings "might motivate further studies [which the authors propose], but are not definitive in themselves," he said. "Hence, there is nothing in this paper to suggest that at this time someone should not consume caffeine for fear of increasing her risk of developing breast cancer."

More information

For more on diet and cancer, visit the American Cancer Society.