Thanks again for the advice Mrs. D. Here's the things I'm going to recommend to him based on what I've found so far:

-Vitamin D (he's already taking this)
-B-12
-Magnesium
-CoQ10
-L-Glutamine

I'm also going to order him a 23andMe genetic test, to see if he has the same MTHFR A1298C mutation that I do. (That would point to some additional supplements as well.)

Anyone else have any ideas or experiences that might help?