Breast cancer may worsen in some women who drink four or more cups of coffee a day, but consuming coffee and other caffeinated beverages doesn't seem to increase the overall risk of getting malignant breast cancer, researchers say.

Caffeine in coffee provides the jolt to smooth the transition from sleep for as many as 80 per cent of North Americans. Also found in tea, pop, chocolate and some medications such as headache and over-the-counter stimulants, caffeine is probably the most commonly consumed drug worldwide, according to agricultural and medical studies.

Among women with benign or non-cancerous breast lesions, scientists noticed that cutting caffeine from the diet tended to reduce symptoms, but the results were not consistent.

Since benign breast lesions also increase the risk of getting breast cancer, researchers in the U.S. and Japan designed a large study to take a closer look at the potential links between caffeine consumption and various types of breast cancer.

In Monday's issue of the Archives of Internal Medicine, Dr. Ken Ishitani of Harvard Medical School in Boston and his colleagues analyzed data from more than 38,000 women 45 years or older who provided diet information from 1992 to 1995.

Women with benign breast disease who were in the top one-fifth for caffeine consumption and drank at least four cups of caffeinated drinks daily showed 1.32 times the risk of switching from benign to malignant breast cancer, the researchers found.

Breast cancers are classified based on whether the tumours are promoted or fuelled by hormones. If a patient is found to be ER/PR (estrogen receptor/progesterone receptor) positive, anti-hormone drugs are prescribed. The prognosis for estrogen receptor positive breast cancer is generally more favourable than for estrogen receptor negative cases.

"There is a possibility that high caffeine consumption increases the chances of developing estrogen receptor negative breast tumours or breast tumours larger than two centimetres," the study's senior author, Dr. Shumin Zhang of the division of preventive medicine at Brigham and Women's Hospital in Boston, said in an e-mail.

In the study, those who consumed high amounts of caffeine had a 1.68 times higher risk of developing estrogen receptor-negative tumours compared with those who almost never drank coffee or consumed caffeine.

High caffeine consumption was also associated with 1.79 times higher risk of developing breast tumours larger than two centimetres.

The results are correlations only and do not provide evidence of a causal link.

On the other hand, reassuringly, consumption of caffeine and caffeinated beverages and foods did not seem to increase the overall risk of getting breast cancer at a statistically significant level, that is, beyond chance alone.

"These data show no overall association between caffeine consumption and breast cancer risk," the study concluded.

"The possibility of increased risk in women with benign breast disease or for tumours that are estrogen and progesterone receptor negative or larger than 2 cm warrants further study."

How caffeine may affect the development of breast cancer is also complex and remains unclear, the study's authors noted.

http://archinte.ama-assn.org/ Archives of Internal Medicine