How much sulforaphane per day

Sulforaphane is not an essential nutrient. Nobody becomes deficient in it, so no agency has set a daily intake or an upper limit. Anyone quoting a "recommended" amount is quoting a trial dose, a supplement label, or a guess. This page covers the first of those, with the method behind every figure. For what the compound is and how it forms, start with the sulforaphane overview.

Is there a recommended daily amount of sulforaphane?

No. Official intake values exist for vitamins and minerals, and sulforaphane is neither. What you can find is the dose a given trial chose to test, in a given group, for a set number of weeks.

Those doses are useful for scale. They tell you what amount researchers thought worth giving to people, and what happened. They do not show that the amount is right for anyone else.

What doses have human trials used?

Trials report doses in micromoles (µmol), because the chemistry works per molecule. The milligram figures below are our arithmetic from the molar masses. The trials did not report them.

Both trials measured specific outcomes and neither was designed to find a best dose. The Qidong trial measured how much people excreted of the breakdown products of benzene and acrolein, two air pollutants. The autism trial measured behavior on rating scales completed by parents, carers and physicians. Neither result tells you what a healthy adult should take.

Why does a glucoraphanin dose deliver so much less?

Most products and many food figures give glucoraphanin, the stable precursor, instead of sulforaphane. Glucoraphanin has to be split by the enzyme myrosinase before any sulforaphane exists, and that step is where most of the dose goes missing.

A 2015 Johns Hopkins study put numbers on it in a small group, five volunteers for most comparisons. Given glucoraphanin with no active plant enzyme, they excreted about 10 percent of the dose as sulforaphane metabolites. When broccoli sprouts or seeds with their own myrosinase still active were given, recovery rose to almost 40 percent. The doses were measured by HPLC and the urinary metabolites by cyclocondensation assay.

The Qidong trial found a similar pattern at scale. Median excretion among people drinking the beverage was 8.4 to 9.7 percent of the daily dose as metabolites across the 12 weeks, measured by isotope-dilution mass spectrometry. An earlier study from the same Hopkins group found that chewing fresh sprouts thoroughly gave higher excretion than swallowing them whole, because chewing brings the plant's enzyme into contact with glucoraphanin.

The figures differ between studies, but they point the same way: 100 µmol of glucoraphanin on a label and 100 µmol of sulforaphane in a capsule are very different doses.

How do you convert micromoles to milligrams?

Multiply micromoles by the molar mass, then divide by 1,000. Sulforaphane has a molar mass of 177.3 g/mol, so 1 µmol is 0.177 mg. Glucoraphanin has a molar mass of 437.5 g/mol, so 1 µmol is 0.4375 mg.

This is why a glucoraphanin label can look large. A capsule with 30 mg of glucoraphanin holds about 69 µmol. Even if all of it converted, that would make about 12 mg of sulforaphane, and the studies above show that most of it does not convert.

How much sulforaphane do broccoli sprouts provide?

Broccoli sprouts are the richest common food source of glucoraphanin, and they carry their own active myrosinase when eaten raw. That is why the 2015 study saw higher recovery from sprouts than from glucoraphanin alone. The broccoli sprouts section covers them in detail, including how to grow broccoli sprouts at home.

A per-gram figure is harder. Published glucoraphanin content for sprouts varies widely between seed lots and growing conditions, and this site does not quote one without its assay. Measured values, each with its method, are going into the sulforaphane content by food table as they are verified.

Is there a maximum safe dose?

No upper limit has been set, and no trial has run long enough or large enough to find one. The evidence on safety is thin and short-term.

A 2006 phase I study kept 12 healthy volunteers on a research ward, nine taking broccoli sprout extract and three placebo, with doses every eight hours for seven days. The researchers ran 32 types of blood test, including liver and thyroid function, and saw no toxic effects. Nine people for one week cannot reveal a rare or slow-developing problem.

The 18-week autism trial recorded vomiting, abdominal pain, flatulence, constipation, diarrhea, irritability and several other complaints in 12 to 19 percent of participants on sulforaphane. The authors report the same incidence in the placebo group. Two participants each had a single seizure, one after three weeks on sulforaphane and one three weeks after stopping, and both had a history of seizures. The authors wrote that they could not rule out seizures as an adverse effect in autism. The sulforaphane side effects page covers what trials have reported and who has reason for caution.