Narrative reviewindependent cross-checkabstract checked I-VEG-128 standard review
Most brassicas carry little goitrogen
Concentrations of thiocyanate and goitrin in human plasma, their precursor concentrations in brassica vegetables, and associated potential risk for hypothyroidism.
Overview
Felker P et al.. Nutr Rev 2016 · PMID 26946249 · DOI 10.1093/nutrit/nuv110
Only a few varieties (collards, Brussels sprouts, some kale) contain enough goitrin to possibly reduce iodine uptake; broccoli and most kale contain little.
Does the study support the specific claim? Partly · Methodological quality: low
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Quantify goitrogen content of brassicas.
- How was the study done?
Review.
- How many people, animals or samples were studied?
Not applicable.
- What was actually found?
Risk depends on variety and amount.
- How large was the observed effect?
194 umol goitrin threshold.
- What do the results mean in everyday life?
Very large amounts of certain raw brassicas could matter for people low in iodine.
- What are the study's limitations?
Narrative; industry authors.
- What does it say about Elawady's specific claim?
Partly supports a conditional version.
- Do the results apply to Germany and Europe?
Applicable.
- What can explicitly not be concluded from this study?
Cannot show harm at normal intakes.
Scientific in-depth review
1. Full reference
- Authors
- Felker P et al.
- Journal
- Nutr Rev
- Year
- 2016
- Identifier
- PMID 26946249 DOI 10.1093/nutrit/nuv110
- Verification
- verified – PubMed efetch 2026-10-26; Crossref 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
not stated in abstract; two of three authors affiliated with D'Arrigo Bros. Co. (a vegetable producer) per PubMed affiliation; NIH grant listed
2. Research question
Which brassica vegetables contain enough goitrin or thiocyanate precursors to affect thyroid iodine uptake?
3. Study design and population
- Study design
- Narrative review – Review of goitrin/thiocyanate concentrations in brassica vegetables and plasma, with dose thresholds from human studies
- Population
Not applicable
- Country
USA (authors)
- Period
not applicable
- Sample size
not applicable
- Inclusion and exclusion criteria
not stated in abstract
4. Methods and endpoints
- Exposure / intervention
Goitrin and indole glucosinolate content of brassica varieties
- Comparator
Thresholds (194 vs 77 umol goitrin)
- Endpoints
Radioiodine uptake inhibition
- Statistical methods
Narrative/quantitative comparison
5. Actual results
- Results
Radioiodine uptake inhibited by 194 umol goitrin but not 77 umol. Collards, Brussels sprouts and some Russian kale (B. napus) contain enough goitrin to potentially decrease iodine uptake; turnip tops, commercial broccoli, broccoli rabe and kale (B. oleracea) contain <10 umol per 100-g serving (minimal risk). Thiocyanate from indole glucosinolates (max ~10 uM) is well below background plasma levels (40-69 uM).
- Absolute risks
not reported
- Authors' conclusion
Most brassicas pose minimal thyroid risk; a few varieties contain enough goitrin to potentially reduce iodine uptake.
6. Strengths
- Quantitative, variety-specific
7. Weaknesses
- Narrative
- Industry-affiliated authors
8. Risk of bias
- Orienting tool
- none applicable
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Two authors affiliated with a vegetable producer (D'Arrigo Bros., per PubMed affiliation).
9. Assessment of the statistical interpretation
Threshold-based comparison only.
10. Relevance to the specific claim
Mixed: a goitrogenic effect is possible for some varieties at high intakes, minimal for most.
11. Independent contrary findings
Galanty 2024.
12. Transferability to Germany and Europe
Applicable.
13. Overall methodological judgement
Supports a conditional, dose- and variety-dependent concern, not a general one; bok choy-type myrosinase activity in raw form is relevant to the single reported case.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | low |
| Risk of bias | some concerns |
| Precision of results | not applicable |
| Directness | indirect |
| Reproducibility | unknown |
| Consistency with the overall evidence | mixed |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Human data for bok choy specifically.
15. Linked fact checks
- Raw cruciferous greens such as bok choy suppress the thyroid (glucosinolates) and can cause myxedema coma. – Studies with mixed or unclear results