Fluoride is the most electronegative of the halides. That means fluoride atoms are extremely reactive in the human body. And fluoride is not an essential element. Humans have no need for it, nor do we have receptors that require it.

In infants and children, approximately 80 percent to 90 percent of absorbed fluoride accumulates in the body. And fluoride is known to bind to nerve tissues, as well as tissues high in calcium (teeth and bones).

Long-term exposure to fluoride during prenatal and postnatal development has a toxic influence on metabolism, as well as the physiology of neurons and immune cells of the central nervous system — called glial cells — which results in learning and memory deficits.

Fluoride is also known to cross both the blood-brain barrier and the placenta barrier. Therefore, the toxicity of fluoride is accelerated in utero as well as in young children.

Exposing adult mice to fluoride has resulted in marked disruption of the normal architecture of the animals’ brains. And fluoride makes the volume of the brain smaller.

Animal studies have also shown excess production of reactive oxygen species in the mitochondria of nerve cells. This damages the ability of the mitochondria to produce the energy molecules that fuel normal neurological function.

For more than 60 years, there has been concern that perinatal and long-term exposure to fluoride could result in lower IQs in children. A Canadian study found that a small increase — 0.5 mg/L — in drinking water fluoride concentration for women who had hypothyroidism (which is linked to fluoride exposure) was associated with a lower IQ in children. The same study found a 65 percent increase in risk of the children having primary hypothyroidism.

Other studies have found higher fluoride levels in drinking water is associated with increased risk of hypothyroidism in both children and adults.

Compared to adults living in nonfluoridated areas, an English study found a 60 percent higher risk of hypothyroidism among those living in fluoridated areas