From the article
>Let’s start with a simple, low-stakes example: fluoridated drinking water. On the one hand, fluoride is a simple ion that shows up in various concentrations, including naturally through calcium fluoride, in bodies of water all across the world. When humans ingest too little of it, particularly at a young age, it leads to weakened tooth enamel and greater rates of cavities; when humans ingest too much of it, it leads to tooth discoloration and various severities of dental fluorosis. In extreme cases, significantly too much or too little fluoride can also lead to other problems, such as osteoporosis (with too little) or skeletal fluorosis (with too much).