Yes there is a lot of causes for depression; Hypo Thyroid is one of them; anxiety is within the picture too.
My eldest kid is much better of these things after iodine, magnesium etc; but it take a bit of time; months at least. I usually say a year to my cases; before they are much better.
Nows boron are fine; but I would take more than the rec 3 mg; 9-12 is more in the terapeuthic range. + the magnesium; http://www.real-depression-help.com/magnesium-for-depression.html