Urinary excretion of isothiocyanates – bioactive compounds derived from cruciferous vegetables – is associated with a lower risk of breast cancer, a 2003 study found. Women with the highest levels of isothiocyanates in their urine were half as likely to have breast cancer, compared to women with the lowest levels.

Researchers measured isothiocyanates in the urine of 674 women, half of whom had breast cancer. They also collected information about the women’s demographics, lifestyles, reproductive histories, and dietary intake of cruciferous vegetables.

They found high urinary isothiocyanate levels reduced the women’s risk of having breast cancer by half, even after considering age, menopausal status, and other factors that influence breast cancer risk. This protective association was true in pre- and postmenopausal women.

Isothiocyanates are bioactive compounds derived from glucosinolates, a large class of precursor molecules found in cruciferous vegetables. Robust evidence demonstrates that isothiocyanates switch on the activity of cellular protective mechanisms that reduce the risk of many chronic diseases, including cancer.

Assessing isothiocyanate exposure via dietary reports of glucosinolate intake is often inaccurate due to reporting biases as well as differences in plant glucosinolate content, which varies across species and cultivars. In addition, inter-individual differences in how people metabolize isothiocyanates and their precursors may influence exposure. Measuring urinary isothiocyanate metabolites likely provides more accurate measures of habitual intake and metabolite-specific exposures that positively influence risk.

Sulforaphane is an isothiocyanate with potent antioxidant, anti-inflammatory, and anticancer properties. Learn more about sulforaphane’s effects on cancer in this clip featuring Dr. Jed Fahey.

• Read study abstract.

• Read more about sulforaphane, a type of isothiocyanate, in our overview article.