Vitamin B3. Nicotinamide is the active form of niacin, and it is the precursor of coenzymes NADH and NADPH, which are essential for over 200 enzymatic reactions in the organism, especially the production of adenosine triphos- phate (ATP). Meat, fish, and wheat are generally rich in nicotinamide, while vegetables have a low nicotinamide content [21]. Deficiency of nicotinamide/niacin can lead to pellagra, causing dermatitis, diarrhea, and depression [22]. Nicotin- amide has neuroprotective and antioxidant functions at low doses but exhibits neurotoxicity, especially dopaminergic toxicity, at high doses [23]. Fukushima also suggests that excessive nicotinamide is related to the development of PD [24]; excessive nicotinamide can induce overproduction of 1-methylnicotinamide (MNA), which is increased in patients with PD [25]. In an in vitro study, Griffin et al. found that low-dose nicotinamide (10mM) has a significant effect on inducing differentiation from embryonic stem cells into neu- rons; however, higher doses (>20mM) of nicotinamide induce cytotoxicity and cell death [26]. The definitive protecive dose of vitamin B3 still needs further researches.