Concentrations of thiocyanate and goitrin in human plasma, their precursor concentrations in brassica vegetables, and associated potential risk for hypothyroidism.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing published thresholds and pharmacokinetic modeling without original human trial data
PubMed 26946249 · doi:10.1093/nutrit/nuv110
What was done
This narrative review analyzed published literature on precursor glucosinolate concentrations in various brassica vegetables and the threshold levels of their breakdown products (goitrin and thiocyanate) required to inhibit thyroid function. The authors compared vegetable goitrin content against known human radioiodine uptake inhibition thresholds and estimated plasma thiocyanate contributions using pharmacokinetic surrogate data from glucoraphanin.
What was found
Radioiodine uptake by the thyroid is inhibited by 194 μmol of goitrin, but not by 77 μmol. Collards, Brussels sprouts, and some Russian kale (Brassica napus) contain sufficient goitrin per serving to potentially inhibit thyroid iodine uptake. Turnip tops, commercial broccoli, broccoli rabe, and Brassica oleracea kale contain less than 10 μmol goitrin per 100-g serving. Estimated maximum plasma thiocyanate contribution from indole glucosinolates is 10 μM, compared to background plasma levels of 40–69 μM.
Why it matters
Most commonly consumed brassica vegetables contain negligible goitrin and pose minimal risk for thyroid impairment. However, excessive consumption of specific types like collards or Brussels sprouts could potentially affect thyroid iodine uptake.
Limits
The review relies on indirect pharmacokinetic modeling and surrogate markers rather than direct clinical trial measurements. Number of included studies and overall data volume are not specified in the abstract. Inter-individual metabolic variation and dietary preparation effects were not directly evaluated.
Cited by
- contradicts Mature broccoli is a goitrogen, whereas broccoli seeds and sprouts are not goitrogenic.