For many years, it has been known that compounds called goitrogens can interfere with the normal function of the thyroid gland, preventing the incorporation of iodine into the hormones the thyroid gland produces. Such goitrogenic compounds are found in certain cruciferous vegetables. This has led to widespread confusion because it has been assumed by many (including clinicians) that all cruciferous vegetables are equally goitrogenic. This is not the case.
How do Goitrogens form?
Progoitrins are precursors to the goitrins. In the case of broccoli, the progoitrins develop as the vegetable matures and are virtually non-detectable in the seed or sprout but increase as the vegetable grows to maturity. For the progoitrin to convert to the goitrin, it needs to be converted by activation of an enzyme known as myrosinase and found in the plant cell. If broccoli or the other crucifers are cooked, the myrosinase enzyme is destroyed and the goitrins aren’t produced.