Wednesday Jan 14, 2015 (foodconsumer.org) -- A new study in the current issue of Journal of the National Cancer Institute suggests that high dietary intake of folate or folic acid or vitamin B9 may lower risk of certain types of breast cancer.

The study led by Jordi de Batlle, PhD, at International Agency for Research on Cancer in Lyon, France and colleagues showed that overall, women in the highest quintile of dietary folate intake were 8% less likely to be diagnosed with breast cancer, compared with those in the lowest quintile.

In the European Prospective Investigation into Cancer and Nutrition (EPIC) study, 367,993 women aged 35 to 70 years from 10 European countries were followed for a median 11.5 years during which 11,575 women were diagnosed with breast cancer.  Dietary intake of folate was estimated from country-specific questionnaires.

Specifically, among premenopausal women, those in the highest quintile of dietary intake of folate were found 34% less likely to develop estrogen receptor-negative breast cancer and 30% less likely to develop progesterone receptor-negative breast cancer, compared with those in  the lowest quintile of dietary folate.

No association between dietary folate intake and risk of breast cancer was found among postmenopausal women.

Among women who had greater than 12 alcoholic drinks per week, those in the highest tertile were 14% less likely to be diagnosed with breast cancer than those in the lowest tertile of dietary folate.

The study concluded "Higher dietary folate intake may be associated with a lower risk of sex hormone receptor negative BC (breast cancer) in premenopausal women."

Some early studies suggest that dietary folate but not supplemental or fortified folate can cut the risk of breast cancer.  Supplemental folate and fortified folate are often synthetic and it remains unknown whether the synthetic folate can help reduce the risk.  

Folate was added to wheat flour and other foods to help prevent birth defects.  While this fortification is a benefit for child-bearing women, some studies suggest that added folate may do more harm than good to women who do not want children or postmenopausal women as added folate has been linked to some health risk.

For instance, a study published in 2014 in International Journal of cancer suggests that fortification of folate in wheat flour and processed foods may boost the risk of breast cancer in European American women, if not all women.

This same study also found that dietary folate or folate from diet was associated with about 40% reduced risk of breast cancer and ER positive breast cancer in Black American women.

Natural folate is found high in plant-based foods including beans, lentils, spinach, asparagus, lettuce, avocado, broccoli, and oranges.  No evidence suggests that high intake of natural folate causes any harm. 

Caution needs to be exercised when you consider using folate supplements or supplements with synthetic folate.   Also bear in mind that supplemental folate and even multivitamins should not be a substitute for a nutritionally balanced diet.  (David Liu, PHD)