Besides frustrating changes to their hormones, muscle mass and skin, quadragenarians like Kardashian and Johnson also have to worry about a drop in their nicotinamide adenine dinucleotide (NAD⁺) levels. Instagram/@bryanjohnson_Found in all living cells, the molecule plays a key role in cellular energy production, mitochondrial function, DNA repair and metabolism. That’s why Kardashian and Johnson have turned to nicotinamide mononucleotide (NMN) oral supplements to boost their NAD⁺ levels. By supporting NAD⁺ levels, NMN may improve mitochondrial energy production, insulin sensitivity, muscle function and vascular health. NAD⁺ levels can be measured with specialized blood tests.