ABSTRACT
BACKGROUND: Transcranial direct current stimulation (tDCS) of the human brain increases systemic glucose tolerance. OBJECTIVE/HYPOTHESIS: To investigate whether this effect persists after one week of repeated stimulation. Because systemic glucose uptake relates to brain energy homeostasis, we concomitantly measured cerebral high-energy phosphate metabolites. METHODS: In a sham-controlled crossover design, 14 healthy men were tested under daily anodal tDCS vs. sham for 8 days. Systemic glucose metabolism was examined by concentrations of circulating glucose and insulin. Cerebral energy metabolism - i.e. adenosine triphosphate (ATP) and phosphocreatine (PCr) levels - was assessed by 31phosphorous magnetic resonance spectroscopy. RESULTS: Blood glucose concentrations were distinctly lower upon tDCS compared with sham stimulation on day 1. This effect persisted on day 8, while serum insulin levels remained persistently unchanged. Transcranial stimulation increased mean levels of ATP and PCr compared with sham on day 1 only. Blood glucose concentrations negatively correlated with PCr content after repeated daily stimulation. CONCLUSIONS: Our data confirm that tDCS reduces blood glucose through an insulin-independent mechanism. This effect persists after 8 days of repeated stimulation and relates to brain energy metabolism. Therefore, transcranial electric stimulation may be a promising non-pharmacological adjuvant option to treat systemic disorders such as glucose intolerance or type 2 diabetes mellitus with a low side-effect profile.
