After reading through findings of several dozen rodent studies this evening, I thought it would be worthwhile to revisit analysis of human relevance provided by one paper of How much sulforaphane is suitable for healthy people?
“Comparisons of published oral doses of sulforaphane administered to mice or rats and sulforaphane (tablets or sulforaphane-rich broccoli preparations) or glucoraphanin-rich broccoli preparations administered to humans.
The allometric scaling of the murine doses uses the correction factor of 0.081 and those for rat doses 0.162. Human doses were based on an estimate of 70 kg body weights in each study.”
A confession followed:
“Animal studies have not delivered all that might be expected of them. Pre-clinical experimentalists have not thought carefully about the selection of dose (or route) and its relevance to clinical utility.
Over two-thirds of the animal studies have used doses that exceed the highest (and bordering on intolerable) doses of sulforaphane used in humans.
Few studies have included a dose-response. The greater than 4-log spread of doses used in mice appears to be driven by needs for effect reporting in publications rather than optimization of translational science.
Authors of this review have contributed to this dose skewing.”
Let’s narrow this graphic to a human-relevant range:
48 of the 114 rodent study doses were in an allometric range applicable to humans.
Clinically relevant sulforaphane human doses start at a 100 µmol amount (17.73 mg). The graphic normalized human weights to 70 kg, so 100 µmol / 70 kg is 1.43 µmol / kg. Eyeballing the graphic, 43 of the 114 rodent study doses were in an allometric range applicable to human clinical doses.
But only three of the human sulforaphane study doses were above 4 µmol / kg. This indicator of the mentioned “intolerable doses” will limit clinically relevant oral doses to no more than 17.73 mg x (4 / 1.43) ≈ 50 mg in one serving.
Reviewing clinical trials of broccoli sprouts and their compounds described a sulforaphane study with doses above 4 µmol / kg:
“They proposed the intake of 15 capsules of broccoli sprouts at a time, giving 90 mg [508 µmol, 7.26 µmol / kg] of SFN and 180 mg of glucoraphanin, a never before tested dosage, which was established because of the poor life expectancy of the patients and the aggressive characteristics of this type of cancer.
Secondary effects of the chemotherapy, the lack of appetite, nausea, vomits, diarrhea, mouth sores, etc., were factors that made it very difficult for the patients to intake 15 pills at once, as the study initially planned.
Progression of the pancreatic cancer and the GI symptomatology led to a high rate of drop-off of:
- 72% in the treatment group; and
- 55% abandonment in the control group!
Therefore, the results were not significant.”
Our model clinical trial Effects of long-term consumption of broccoli sprouts on inflammatory markers in overweight subjects calculated subjects’ mean weight in Table 1 as “85.8 ± 16.7 kg.” Its average glucoraphanin dose per kg body weight was 117 μmol / 85.8 kg = 1.36 μmol / kg.
Per Estimating daily consumption of broccoli sprout compounds, my twice-a-day consumption of a total 131 grams microwaved broccoli sprouts represents a worst-case 52 mg sulforaphane daily intake. This is ≈ 3 µmol / kg per day, the graphic’s second-largest sulforaphane amount cluster. Half that per serving.
Only 8% of the rodent studies were in a sulforaphane range that was both:
- Clinically relevant to humans as a lower boundary (1.43 µmol / kg); and
- Tolerable to humans as an upper boundary (4 µmol / kg).
The main purpose of animal studies is to help humans. Which researchers conducted sulforaphane studies that could actually help humans?