A substantial body of evidence from experimental, epidemiological, and clinical studies demonstrates the beneficial effects of sulforaphane consumption on human health. Many questions remain, however, regarding optimal formulation, bioavailability, and dosage of sulforaphane. A 2019 review discusses these and other aspects of the current state of evidence surrounding sulforaphane.
Sulforaphane is the end-product of a chemical reaction between two naturally occurring plant compounds – glucoraphanin and myrosinase. These compounds, often referred to as secondary metabolites, are not required for the plant’s growth or reproduction. Rather, they confer an advantage to the plant, particularly in terms of defense, participating in a dual-component chemical defense system – commonly referred to as the “mustard oil bomb” – that protects plants from environmental stressors. Glucoraphanin content in broccoli sprouts and mature broccoli vary across species and cultivar and is influenced by factors such as soil and growing conditions, harvest time, and post-harvest storage.
Most rodent studies of sulforaphane’s effects administer the end product via oral, intraperitoneal, or topical means. The median effective dose is 175 micromoles (~30 milligrams) per kilogram of the animal’s body weight when given orally; the median effective dose when given intraperitoneally is 113 micromoles (~20 milligrams) per kilogram. Most studies report beneficial outcomes, but this might be due to publication bias – the tendency for researchers to publish favorable results only. High doses (greater than 150 milligrams) elicited negative effects, including sleepiness, hypothermia, impaired motor coordination, and even death. When given with other drugs, sulforaphane potentiated some of the drugs' effects.
In humans, sulforaphane undergoes extensive biotransformation in the gut to yield mercapturic acid, which can be measured in urine and serves as a biomarker of intake. In general, sulforaphane is rapidly absorbed and eliminated, with most people excreting between 70 and 90 percent of the dose taken.
Clinical studies have assessed the merits of sulforaphane in a wide range of chronic and infectious diseases, including autism, aflatoxin toxicity, air pollution detoxication, cancer, cardiovascular disease, diabetes, neurodegenerative disease, Helicobacter pylori infection, and many others. Doses varied markedly and in terms of whether supplied as glucoraphanin (the precursor) or sulforaphane (the end product). The median dose of glucoraphanin was 190 micromoles (~76 milligrams) and of sulforaphane was 100 micromoles (~18 milligrams).
The authors of the review enumerate several issues that must be overcome in designing and conducting clinical studies with sulforaphane, but they stress the importance of plant-based diets as delivery modes for not only sulforaphane but other bioactive compounds that promote health. They also noted concerns that determining dose is inherently difficult in light of the differences in bioavailability of glucoraphanin and sulforaphane; translating animal data to humans poses many challenges.
