Thyroid function, vegetables

I've read that several vegetables such as broccoli contain chemicals called goitrogens that inhibit thyroid function.  

Does anyone know if steaming inactivates these compounds?  The evidence seems mixed---some say it completely inactivates them, other say it only minimally inactivates them so they should be eaten sparingly.  Still others say the jury is out.  

Is there any solid evidence whether or not steaming broccoli, cauliflower,... inactivates goitrogens so they can be eaten daily without affecting thyroid function?