Broccoli Sprouts and Sulforaphane

What it is

Broccoli sprouts are young broccoli seedlings. They are the richest source of sulforaphane [1]. The body forms sulforaphane from its inactive precursor glucoraphanin, and gut bacteria affect how well this happens [2].

How it might work

Proposed mechanism: sulforaphane switches on the body's antioxidant and phase II enzymes [1]. In the blood sugar trial, gut bacteria that convert the precursor to sulforaphane seemed to shape who responded [2]. The autism trial authors proposed that sulforaphane could reverse the oxidative stress and inflammation seen in autism [3].

What the research says

A 12-week trial in 74 people with prediabetes found fasting blood sugar fell about 0.2 mmol/L more than with placebo, though the main target was missed [2]. A 4-week trial in 63 people with type 2 diabetes found insulin and insulin resistance fell with 10 grams of sprout powder a day [4].

Two trials of high-glucoraphanin broccoli (130 people) found LDL cholesterol fell 5 to 7%, against about 2% on standard broccoli [5].

In a trial of 44 young men with autism, behaviour scores improved 34% on one checklist, against little change on placebo [3]. A trial in 40 children found no significant change [6].

In 70 children with ADHD, sulforaphane added to methylphenidate gave larger symptom drops than methylphenidate with placebo [7].

In 47 people with hay fever, sprout extract added to a nasal steroid spray improved nasal airflow more than spray with placebo [8].

In 37 former smokers, a 12-month trial lowered a cell-growth marker in airway tissue but did not change biopsy scores [9].

In 40 adults with asthma, three days of sprouts did not reduce airway inflammation or improve lung function [1].

In an observational meta-analysis of broccoli eating in general, cohort studies showed an 11% lower cancer risk [10].

Doses used in studies

Doses ranged from 10 grams of sprout powder a day for 4 weeks [4] and 100 grams of sprouts a day for 3 days [1] to 30 mg of sulforaphane a day for 4 to 8 weeks [11][7], 50 to 150 micromoles a day for 18 weeks [3], and 95 micromoles a day for 12 months [9]. These are trial doses, not recommendations.

Safety and interactions

Side effects: stomach upset was the main complaint, with no severe adverse events in the blood sugar trial [2]. Thyroid function was unchanged after 84 days of a sprout-derived beverage in 45 women [12].

Medicine interactions: sulforaphane alone did not change CYP3A4 activity across 24 adults, but in those with the highest starting activity it lowered it [13].

Upper intake limits: none were reported in the studies read.

Pregnancy and breastfeeding: the studies read did not report data on these groups.

People with kidney disease: in 25 people on hemodialysis, sulforaphane did not change inflammation-related gene expression, and the trial did not report safety for that group [14]. Ask a doctor before use if you have kidney disease or take medicines.

Caveats and open questions

Most human trials are small and short. Blood sugar and cholesterol results are based on blood markers, not diagnosed disease [2][5].

The blood sugar trial and the autism trial have patent or licence ties to sulforaphane companies [2][3].

About half of completed sulforaphane trials remain unpublished, so the picture may be incomplete [15].