Manganese (Mn) is an often overlooked but important nutrient, required in small amounts for multiple essential functions in the body. A recent study on cows fed genetically modified Roundup^®-Ready feed revealed a severe depletion of serum Mn. Glyphosate, the active ingredient in Roundup^®, has also been shown to severely deplete Mn levels in plants. Here, we investigate the impact of Mn on physiology, and its association with gut dysbiosis as well as neuropathologies such as autism, Alzheimer’s disease (AD), depression, anxiety syndrome, Parkinson’s disease (PD), and prion diseases.