Thyroid and broccoli: perfectly safe

Posted on Mon, 26 Sep 16

People worried about broccoli and other vegetables in the brassica family can safely consume them as they do not cause hypothyroidism or goiter, according to research. 

For some time, there has been potential concern that broccoli and other vegetables in the same (brassica) family such as kale, cabbage, and Brussels sprouts could cause hypothyroidism or goiter. 

These vegetables do indeed contain substances that could negatively affect thyroid function referred to as “goiterogens,” but advice to avoid these foods has largely been speculative. 

Concerns are related to a substance called methylthiobutyl glucosinolate that can be metabolized into progoitrin, a goiterogen that can decrease iodine uptake into the thyroid and reduces the synthesis of thyroid hormones.

However, a comprehensive assessment published in Nutrition Reviews looked at the evidence and found that usual dietary intakes are far lower than those that could ever negatively affect your thyroid [1]. This is especially true if you cook them, as it de-activates the goiterogen.  

An exception is if you were to eat certain species particularly high in goiterogens, such as Russian/Siberian kale, some collards, and Brussels sprouts, but you would have to consume over one kilogram of un-cooked or raw vegetables every day for several months before you developed symptoms. 

So at usual intakes you can safely enjoy Brassica vegetables, which is good news as they are associated with a wide range of health benefits.

Reference: 

1. Felker P, Bunch R, Leung AM. Concentrations of thiocyanate and goitrin in human plasma, their precursor concentrations in brassica vegetables, and associated potential risk for hypothyroidism. Nutr Rev. 2016 Apr;74(4):248-58.