Dose matters: New research demonstrates that sulforaphane from broccoli sprouts combats a cause of air pollution injury in a dose-dependent manner

Air pollution contains many toxic substances. One of these substances, benzene, is known to cause cancer in humans. A new study led by the Cullman Chemoprotection Center’s scientific partner, Dr. Tom Kensler, found that sulforaphane provided in a broccoli sprout beverage increased the body’s excretion of benzene in a dose-dependent manner. The findings were published on July 3 in the American Journal of Clinical Nutrition.

Sulforaphane is the end product of a reaction between two chemicals produced in broccoli and broccoli sprout plants. When people chop or chew the plants, the two chemicals come together to form sulforaphane. It is what gives broccoli and broccoli sprouts their pungent flavor.

Sulforaphane switches on cellular pathways that protect cells from exposure to environmental carcinogens. It also promotes the production of chemicals that facilitate the body’s excretion of toxic substances. When these chemicals bind with toxins like benzene, they form new chemicals, often referred to as metabolites, which can be excreted (and measured) in urine. One class of these metabolites, called mercapturic acids, forms when the powerful antioxidant glutathione binds with benzene.

Exposure to the chemicals in air pollution kills or sickens roughly seven million people every year. China has the highest levels of air pollution anywhere in the world. Previous studies conducted by Dr. Kensler’s research team in Qidong, China, demonstrated that sulforaphane enhanced benzene excretion, as measured by mercapturic acid levels in urine.

The researchers conducted a new study to determine the optimal dose of sulforaphane to promote benzene excretion. The study involved 170 healthy adult participants between the ages of 21 and 65 years living in Qidong. “This work was conducted in an ‘otherwise healthy’ population that is being exposed to constant and sometimes high levels of air pollution, so one could argue that they are not ‘otherwise healthy,'” said Dr. Jed W. Fahey, director of the Cullman Chemoprotection Center and a collaborator on the study.

Twice a day for a period of 10 days, the participants drank a placebo or a broccoli-sprout beverage containing one of three doses of sulforaphane – “high,” “medium,” or “low.” After drinking the beverage, the participants provided a urine sample, which was assessed for benzene metabolites.

The researchers found that the high dose of sulforaphane markedly increased the production of several urinary metabolites. In particular, excretion of mercapturic acids increased by more than 63 percent in those taking the high dose. Mercapturic acid excretion in those who received the medium and low dose, however, was not significantly different from the placebo controls.

These findings demonstrated that a broccoli sprout beverage containing sulforaphane enhanced the detoxication of benzene, an important airborne pollutant. “The tremendous joint effort in Qidong, China, has finally started to put some points on the dose-response curve showing the biological detoxification activity of sulforaphane in a clinical population,” said Dr. Fahey. “This work should greatly bolster the concept that frugal, population-based strategies for improving healthspan with a dietary approach can work!”

Teresa Johnson

Teresa L. Johnson, MSPH, RD, is a freelance science writer and health communications consultant with a long-time interest in the role of plant-based diets and cancer prevention. Her work draws on elements of nutritional biochemistry, phytochemistry, and epidemiology.
Teresa Johnson