We investigated the safety and efficacy of oral nicotinamide mononucleotide supplementation in older patients with diabetes and impaired physical performance...We carried out a 24-week placebo-controlled, double-blinded study of male patients with diabetes aged ≥65 years with reduced grip strength (<26 kg) or walking speed (<1.0 m/s). The primary end-points were to determine the safety of NMN oral administration (250 mg/day), and changes in grip strength and walking speed. In older male patients with diabetes and impaired physical performance, NMN supplementation for 24 weeks was safe, but did not improve grip strength and walking speed.