CRUCIFEROUS VEGETABLES AND THE THYROID GLAND: FRIENDS OR FOES? Michael Kob, MD, Division of Clinical Nutrition, Bolzano Central Hospital, Bolzano, Italy
BACKGROUND
RESULTS
Cruciferous (brassica) vegetables are very common foods, especially in plant-based diets. They contain many healthy nutrients, including phytochemicals with anticarcinogenic, antioxidative and antiinflammatory activity[1]. However, they also contain goitrogens[2] such as progoitrin (fig. 1) and thiocyanate-producing indole glucosinolates (fig. 2), which may interfere with thyroid hormone production or utilization (fig. 3). The aim of this evidence-based literature review is to provide information regarding the influence of cruciferous vegetables on thyroid function in humans.
Four observational studies[3,4,5,6], one case report[7], one article investing the goitrogens content of brassica vegetables[8] and three experimental studies were found[9,10,11]. Most of the brassica vegetables have low goitrin contents, with the exception of collards, Brussel sprouts and some Russian kale species (fig. 4). The consumption of 150 g of cooked Brussel sprouts/die for four weeks did not show any negative effect on thyroid parameters[11]. The only studies with negative outcomes were 1) a case report where 1-1.5 kg of raw Bok Choy was consumed daily over several months[7] and
METHODS
2) observational studies from the seventies, where children consumed large amounts of milk by cows fed with high glucosinolate-containing food crops.
A review of articles relating cruciferous vegetables with thyroid function in humans was performed. Fig. 1: Conversion of progoitrin to goitrin by the enzyme myrosinase [2]
Fig. 2: Glucosinate degradation [2]. Indole glucosinates produce thiocyanates
Fig. 3: Inhibitition of the Sodium Iodide Symporter (NIS) and the Thyroperoxidase (TPO) by goitrin and thiocyanates
THIOCYANATES
⊖
GOITRIN
Fig. 4: Thiocyanate-producing glucosinolate and progoitrin concentrations in different cruciferous vegetable[8] THIOCYANATES GOITRIN
900 800
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THIOCYANATE-PRODUCING GLUCOSINOLATE CONCENTRATIONS [umol/100g]
700
PROGOITRIN CONCENTRATION [umol/100g]
600 500 400 300 200 100 0 Kale (B. oleracea leaves)
Kale (B. napus Brussel sprouts leaves)
B. oleracea acephala group (collards)
Broccoli rabe Cima di rapa variants
Chinese cabbage
Turnip tops
Pak Choi
CONCLUSIONS: There is little reliable evidence that the consumption of normal dietary levels of cruciferous vegetables affects thyroid function. Furthermore, the goitrogen-concentration can be decreased by cooking by boiling, which causes leaching of glucosinolates into water and inactivation [12] of the enzyme myrosinase . REFERENCES: [1]Wagner AE et al., Oxid Med Cell Longev 2013; [2]Jahangir M et al., Compr Rev Food Saf 2009; [3]Clements FW, Med J Aust 1957; [4]Chandra AK, Indian J Med Res 2008; [5]Fernando R et al., Int J Int Med 2012; [6]Gaitan E, Annu Rev Nutr 1990; [7]Chu M et al., N Engl J Med 2010; [8]Felker P et al., Nutr Rev 2016; [9]Langer P et al., Endokrinologie 1971; [10]McMillan M et al., Hum Toxicol 1986; [11]Shapiro TA, Nutr Cancer 2006; [12]Rungapamestry V et al., J Agric Food Chem 2006; Contact:
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