Could you please tell if and how niacin (or niacinamide) deficiency play any role in synthesis of tetrahydrobiopterin? thank you.

Reduce synthesis: Niacin deficiency would be expected to reduce synthesis as Niacin is needed to produce NADP and NADP is a co-factor in converting Dihydrobiopterin into Tetrahydrobiopterin, which is needed to synthesize serotonin, dopamine, melatonin, epinephrine , norepinephrine and nitric oxide and to metabolize phenylalanine. Fortunately supplemental niacin and niacineamide are affordable and readily available.