Breast Cancer and Environmental Factors. What Does Science Tell Us?

90% of breast cancer cases are thought to be caused by environmental factors

Breast cancer is the most common cancer among women, in Spain and worldwide. More than 90% of cases are thought to be caused by environmental factors, i.e. external biological, physical or chemical factors.

After much research, today we know some of the factors that can affect the development of this type of cancer. It is important to distinguish between breast cancer affecting women before or after menopause, since the risk factors seem to differ between these two groups.   

Alcohol consumption and a greater height are risk factors

Alcohol consumption and a greater height are risk factors for both groups. In contrast, a diet rich in vegetables, calcium and carotenoids can protect against the disease.

Regarding premenopausal women, studies point to an association between higher weight at birth and breast cancer risk. Intense physical activity and higher body fat – although seemingly contradictory - protect against the disease, as well as the consumption of dietary products. 

In the case of postmenopausal women, specific risk factors include higher body fat and body weight gain in adult life. Breastfeeding is considered a protection factor.  

At ISGlobal, and particularly within the MCC-Spain project, we investigate new environmental factors associated with cancer development. 

On one hand, we are studying the water we drink. During the purification process, a series of disinfection by-products are generated, including trihalomethanes that have been associated with an increased risk of bladder cancer. Nitrates derived from an excessive use of fertilizers or from wastewater could be related to the development of some types of cancer, with a higher risk in postmenopausal women that consume more red meat in addition to drinking nitrate-rich water. To date, our studies have not revealed any association between disinfection by-products and breast cancer. 

To date, our studies have not revealed any association between disinfection by-products and breast cancer

On the other hand, we have also studied whether exposure to artificial light increases cancer risk. We recently published a study associating high levels of blue light exposure at night and increased risk of breast and prostate cancer. 

Another study we performed - that has had great impact in the media and could have important implications regarding cancer prevention guidelines – is one on eating and sleeping schedules. The results showed that people who have their evening meal before 9 pm or wait at least two hours before going to sleep have a 20% lower risk of breast and prostate cancer, as compared to those that dine after 10 pm or go to sleep immediately after supper.  

Working night shifts –something unavoidable in certain professions- has also been associated with a higher risk of breast cancer. 

All the factors that I just listed – artificial light exposure at night, sleeping and eating patterns, night shifts – are associated with changes in the biological clock

All the factors that I just listed – artificial light exposure at night, sleeping and eating patterns, night shifts – are associated with changes in the biological clock, since carrying out activities out of sync with the sun leads to an alteration in the internal metabolism. All this is modulated by each individual’s chronotype, a personal feature that determines the preference for daytime (“lark”-type) versus nocturnal (“owl”-type) activities.    

Last but not least, we also have studied the relation between breast cancer and contact with green spaces. There is increasing scientific evidence that green spaces are beneficial for mental and physical health. In our study, we observed a lower risk of breast cancer among women that live close to green urban spaces.  

These recent discoveries shed some light on the factors that contribute to cancer development, particularly breast cancer. However, we must continue investigating to deepen our knowledge on this disease and learn to better prevent it.