This is a common and destructive mistake
NAC and glycine support internal production
Importantly, more than a half-centurys worth of research involving high-dose NAD+ precursor supplementationalong with clinical studies of over 2,000 participantshas found no evidence linking these compounds to an increased risk of cancer in humans. In fact, some studies suggest the opposite: supplementation with NAD+ precursors may be associated with a lower risk of certain cancers. For example, a large Australian randomized controlled trial found that nicotinamide supplementation significantly reduced the incidence of non-melanoma skin cancer. Additionally, data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2014 revealed an inverse association between niacin intake and mortality among cancer patients. Clinical studies of NR also further support NAD+ precursor safety

Feng L, Cheah IK, Ng MM, Li J, Chan SM, Lim SL, Mahendran R, Kua EH, Halliwell B (2019) The association between mushroom consumption and mild cognitive impairment: a community-based cross-sectional study in Singapore
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