"The NRC Panel concluded that under 4ppm, NO ADVERSE HEALTH EFFECTS OCCUR."
Complete nonsense by Dr. Johnson. The NRC concluded no such thing. Dr. Johnson has been asked repeatedly to provide the specific page citation for the NRC report where any such statement can be found - he never did provide it, as it simply doesn’t exist.
Besides the fact that 4 ppm constitutes a CONCENTRATION - not a DOSE which is what is important in fluoride toxicology, there are many studies showing adverse health effects in areas where the water supply has less than 4 ppm fluoride.
Click here for studies on adverse health effects “below 4 ppm”.