This study will evaluate the effect of repeated doses of Niagen™ on Niagen™ metabolite concentrations in blood, urine and muscle. There will be 3 doses of Niagen™ compared to a placebo. One quarter of subjects will receive the low dose of Niagen™, one quarter will receive the moderate dose of Niagen™, one quarter will receive the higher dose of Niagen™ and one quarter will reveive the placebo.