The more vitamin B3 deficient we are, the more our bodies will divert essential nutrient tryptophan that they need for de novo protein synthesis into vitamin B3 synthesis.
As it does this, there is less tryptophan for serotonin and melatonin synthesis.
Serotonin deficiency does not cause mood problems but it can aggravate them.
Nocturnal or prior-to-sleep melatonin deficiency does not cause sleep problems but it can aggravate them.
Baseline melatonin deficiency during the waking hours will create all kinds of additional health problems.
Given these facts, we would logically assume the person would have problems with mood (most severe cases – depression) and sleep (most severe cases, chronic insomnia).
By the way, do people with demonstrable serotonin deficiency also have sleep difficulties? Easy enough to find out. It is only logical that they would. The pineal gland that makes the melatonin to help us sleep is drawing on that same limited tryptophan pool.
Most important nutrients for good mood and good sleep? Oddly enough, the most important is vitamin B3, a vitamin our bodies have trouble getting enough of, then tryptophan itself, then tetrahydrobiopterin, vitamin B6, Coenzyme A (vitamin B5, cysteine), and S-adenosylmethionine.