The trial has 3 phases, each lasting 12 weeks. During phases 1 and 3, subjects take lipoic acid or placebo tablets, the order to be determined by randomization. Phase 2 is a 12-week washout period. The intervention is lipoic acid 200mg daily for 1 week, 400mg daily for the second week, and 600mg daily for weeks 3-12. Equivalent numbers of placebo tablets will be taken during the placebo phase.