Dog Food Comparison Shows High Fluoride Levels: Health Effects of Fluoride
Fluoride and dental health
During the last 15-20 years there has been a revolution in our understanding of fluoride's effects on teeth. It is now well-established that fluoride exposure is directly and proportionately related to dental fluorosis, a range of adverse health effect that includes mottling, pitting, and weakening of the teeth (Fejerskov 1994; Heller 1997; NRC 2006). At the same time, fluoride helps prevent tooth decay (Aoba 2002; Featherstone 2000).
Fluoride is believed to have contributed to the decline of tooth decay (cavities, also called dental caries) in many developed countries (CDC 2008; Kumar 2008). On the other hand, early exposure to fluoride poses undeniable health risks to children (NRC 2006; Sohn 2008). In the U.S. and worldwide, about 30 percent of children who drink fluoridated water experience dental fluorosis (Brunelle 1987; Heller 1997; Khan 2005). Strong concerns have been also raised about fluoride exposure and the risk of bone cancer (osteosarcoma), adverse effects on the thyroid function, and lowered IQ in children (NRC 2006).
The risks of fluoride are especially high for infants, prompting the American Dental Association (ADA) to issue an "Interim Guidance on Fluoride Intake for Infants and Young Children." ADA recommended that in areas where fluoride is added to tap water, parents should consider using fluoride-free bottled water to reconstitute concentrated or powdered infant formula (ADA 2006).
Much of what is publicized today in caries prevention programs world-wide is derived from the theories generated in the 1950s and '60s when water fluoridation was actively promoted (Aoba 2002; Pizzo 2007). As we know now, the main benefits of fluoride for dental health are derived from surface application on the teeth, not from ingestion (Aoba 2002; Featherstone 2000; Weyant 2004).
Fluoride works primarily via three topical mechanisms which include (1) inhibition of demineralization at the crystal surfaces inside the tooth, (2) enhancement of remineralization at the crystal surfaces (the resulting remineralized layer is has greater resistance to acid), and (3) inhibition of bacterial enzymes (Featherstone 1999). All of these mechanisms are post-eruptive, which means that they operate in the oral cavity after the permanent tooth emerges from the gum (Aoba 2002; Hellwig 2004).
In summary, the value of fluoride-containing toothpaste to dental health is clear (Bratthall 1996; Ismail 2008; Marinho 2008). Fluoride dental products significantly reduce the incidence of cavities (Adair 2001). In contrast, a substantial and growing body of peer-reviewed science strongly suggests that ingesting fluoride in tap water does not provide any additional dental benefits other than those offered by fluoride toothpaste, and may present serious health risks (Fejerskov 2004; Pizzo 2007; Zimmer 2003).
Fluoride's effects on the nervous system and behavior have been actively debated over the past two decades (NRC 2006). Reports from China, India, and Iran have found that children in high fluoride areas had significantly lower Intelligence Quotient (IQ) compared to children in low fluoride areas (Seraj 2006; Tang 2008; Trivedi 2007). These studies examined adjacent areas with drinking water sources naturally high or low in fluoride. Of note, the high-fluoride areas in these studies had fluoride concentration similar to some naturally fluoridated areas in the U.S., indicating the relevance of the lower IQ/fluoride findings to the U.S. public health.
Fluoride exposure causes neurochemical and biochemical changes in the brains of laboratory animals (Li 2003; NRC 2006). Fluoride also increases the production of free radicals in the brain (Chouhan 2008; Zhang 2007; Zhang 2008). Studies of rats exposed to fluoride compounds reported distortions of brain cells and neuronal deformations, and neurodegeneration (Bhatnagar 2002; Shivashankara 2002; Varner 2002). These neurobiological effects are associated with developmental delays, behavioral problems, and possibly dementia in late adulthood (NRC 2006).
Reviewing the overall evidence for fluoride neurotoxicity,the NRC report concluded that the "consistency of study results appears significant enough to warrant additional research on the effects of fluoride on intelligence." That finding was echoed by a December 2006 study published in the prestigious peer-reviewed journal The Lancet that identified fluoride as an “emerging” neurotoxin (Grandjean 2006).
Summarizing the current state of the science, the National Research Council described fluoride as an endocrine disruptor with especially significant effects on the thyroid and parathyroid hormone function (NRC 2006). Fluoride effects on other hormonal organs, such as the pineal gland, the adrenals, the pancreas, and the pituitary also have been reported (NRC 2006).
Effects of fluoride on the thyroid was first reported 150 years ago (Gedalia 1963; Maumene 1854). Fluoride's potential to impair thyroid function is most clearly illustrated by the fact that until the 1970s, doctors in Europe used fluoride as a thyroid-suppressing medication for patients with Graves's disease and symptoms of hyperthyroidism (Galletti 1957; Litzka 1937). 10 studies conducted between 1941 and 1999 found an association between endemic goiter (enlargement of the thyroid gland) and fluoride exposure in countries as diverse as India, South Africa, Kenya, England, and Nepal. Fluoride anti-thyroid effects appear to be especially severe in cases of iodine deficiency, a condition that is on the rise in the United States (NRC 2006).
Fluoride exposure may pose especial risk to the pineal gland, a part of the brain responsible for production of melatonin and maintenance of day-night cycles and sleep patterns and a range of other physiologic functions. The pineal gland is a unique area of the brain which undergoes calcification with age (Akano 2003). Melatonin is produced by the uncalcified pineal gland tissue and higher calcification is associated with decreased melatonin production (Kunz 1999; Mahlberg 2009). As with other calcifying tissues, the pineal gland accumulates fluoride: an aged pineal gland has 600 times more fluoride compared to the muscle tissue (Luke 2001). In animal studies, fluoride impact on the pineal gland caused lower melatonin production, earlier sexual maturation, and altered day-night activity cycle (Luke 1997).
Today, many people living in communities with fluoridated tap water are ingesting doses of fluoride that fall within the range of doses shown to alter thyroid function, elevate the levels of thyroid-stimulating hormone, calcitonin and parathyroid hormone, impair glucose tolerance and increase prevalence of goiter (NRC 2006). The National Research Council report summarized 23 studies that have observed adverse hormonal effects of fluoride at concentrations of 1-4 mg/L in drinking water.
Fluoride link to bone cancer
Fluoride is known to cause different types of genetic damage in mammalian cells, especially chromosomal aberrations (Zeiger 1993). Genetic toxicity of fluoride and its ability to stimulate active, uncontrolled division of bone cells have been long considered as potential contributors to carcinogenicity effects (NRC 2006). Three human epidemiological studies and two long-term animal studies found a link between fluoride and bone cancer (Bassin 2006; Cohn 1992; DHHS 1991; Maurer 1990; Maurer 1993; NTP 1990).