There is strong evidence from epidemiological data to suggest that there is a strong correlation between plasma estrogen level and the risk of development of breast cancer. Results from a large study published in 1996 showed that history of recent oral contraceptive use rather than the duration of oral contraceptive use was related breast cancer risk. This was a large meta-analysis of 53,297 women with breast cancer and 100,239 women without breast cancer. This study found that that there was a 24% increased risk of development of breast cancer in users of oral contraceptives compared to women who never used oral contraceptives. This data has to be interpreted with caution since most of these women were taking older high-dose forms of oral contraceptives and not the currently available low-dose oral contraceptive pills. It is reasonable to assume that risk of breast cancer associated with the newer low-dose oral contraceptives may be less than 24% as seen in the study.
Hormone Replacement Therapy (HRT)
There has been long term controversy over the issue of increased breast cancer risk associated with hormone replacement therapy (HRT). Previous meta-analysis have failed to show any increased risk of breast cancer associated with hormone replacement therapy, however a recent large study has shown that post-menopausal hormone replacement is clearly associated with increased risk of breast cancer. Duration of hormone replacement therapy (HRT) strongly predicts breast cancer risk.
Use of HRT in women who had previous breast cancer
Is it safe to use hormone replacement therapy after diagnosis of breast cancer? This has been the topic of interest in two recent clinical trials from Sweden. Newest of these studies suggest that development of recurrent breast cancer may be related to the type of hormones used in therapy for women after menopause.
A clinical trial named HABITS was prematurely halted in 2003 after it was shown that women with early stage breast cancer who received hormones estrogen and progesterone showed an increased risk of recurrent breast cancer, compared to women who were not receiving hormone replacement.
Results from another recent clinical trial, called the Stockholm trial, used a different hormonal approach compared to HABITS. This study showed no increase in recurrence of breast cancer with hormone replacement therapy.
Since now we have information that hormone replacement therapy increases the risk of breast cancer in women who never had breast cancer, it may be prudent for those women who are breast cancer survivors to stay away from hormone replacement therapy.
Consumption of alcoholic beverages increases the risk of breast cancer in women. Several studies have suggested a link between alcohol use and risk of breast cancer. A large recent study has shown that consumption of as little as half a glass of wine daily may be associated with increased risk of breast cancer. This conclusion comes from a large meta-analysis that was recently published. This study analyzed 121,700 women and followed them from 1976 to 2000. The study found that women who were drinking 5 to 9.9 grams of alcohol (about half a glass of wine) a day had 6 % increased risk of developing breast cancer compared to women who were not drinking alcohol. Women who were drinking 10 to 19.9 grams of alcohol (about one glass of wine) had 21% increased risk of developing breast cancer compared teetotalers. Those who drank more than 20 grams of alcohol faced a 37% increased risk of developing breast cancer. The risk was even higher in postmenopausal women. In 4,671 postmenopausal drinking of just half a glass of wine increased the risk of breast cancer by 18%.
There is no difference in the risk associated with various different kinds of alcoholic beverages. Beer, wine or spirit may be equally dangerous for the development of breast cancer. Increased risk of breast cancer is associated only with regular drinking of alcohol. Women who take an occasional drink may not have increased risk of developing breast cancer. Consistent weekend drinking on the other hand may be still associated with increased risk of breast cancer, since it the average amount that counts. A glass of wine a day carries the same risk as 7 glass of wine on weekend. Again one has to remember that breast cancer occurs as the result of combination of risk factors, and alcohol is only a small issue compared to a strong family history of breast cancer.
High fat diet
The role of high fat diet as a risk factor is still controversial. Recent five-year data from the ongoing Women's Intervention Nutrition Study showed that breast cancer patients who reduced their fat intake from 29% of their daily caloric intake to about 20% - eating about 33 grams of fat a day - had a nearly one-quarter lower rate of cancer recurrence than women who ate an average of 51 grams of fat per day.
Obesity, overeating and inactivity
Over-eating and doing enough exercise may be a bad combination for the development of breast cancer. This is the conclusion of researchers from China and USA from a recent study. This is more applicable for postmenopausal woman. The researchers point to unhealthy energy balance, which means that these women are not spending as much calories as they are taking in, resulting in a net gain in calories. This combination of over-eating and lack of activity may be associated with nearly five-fold increase in the risk of breast cancer. Simple over-eating if combined with adequate physical activity on the other hand is not associated with significant increase in the risk of breast cancer. It is the combination of over-eating and lack of physical activity that is particularly dangerous in terms of the increased risk of breast cancer. Obesity has also been shown to be a separate risk factor for breast cancer. Obesity may produce alterations in the endogenous estrogen levels and this may in turn lead to higher risk of breast cancer.