Niacin
PD patients are found to have significantly decreased niacin levels compared to age-matched healthy controls [52]. This has been attributed to both the disease itself and the medication used to attenuate motor symptoms [58]. Sinemet, the most commonly used PD medication, includes carbidopa, which prevents the conversion from l-dopa to dopamine within the peripheral nervous system. This allows more dopamine to be taken up by the central nervous system and used where it is scarce after dopaminergic cell loss. Unfortunately, a consequence of carbidopa is reduced conversion of tryptophan to niacin. Sinemet dose and frequency are increased over time as PD symptoms worsen, but concurrently side-effects also worsen.