Nad is slang for one testicle. Im believe he is referring to NAD+ (nicotinamide adenine dinucleotide).
look up copper nicotinic acid (mercola, others).
if memory serves, this is a critical precursor to a reusable cell enzyme that supports many things, but critically it is used to repair damaged dna.
in youth it is plentiful, but as you age, it is not restored but is depleted exponentially.