Read this before selecting your toothpaste !

Fluoride is considered as a trace mineral which is needed in small amounts  for human growth and development. It is beneficial in the maintenance and solidification of our bones, dental health- especially in prevention of tooth decays. Also Fluoride is involved in a number of enzymatic reactions in our body. However, if it is used frequently and absorbed too much it may adversely effect our health. 

Fluoride is present in drinking water, air, dental products, food, beverages and salt. It presence in drinking water is a natural occurring. Here it is present in small quantity(<1.5 mg/l). According to WHO guidelines regarding drinking water the quantity of fluoride  allowed is 1.5 mg/ l. However, studies of groundwater sources in our country show that in the entire Northern, North Central, UVA and Eastern Provinces, and also in a large area of the North Western Province, the Fluoride content in groundwater is within the range 1.0 mg/l and 3.0 mg/l. 
Other than groundwater, most people forming our population are exposed to fluoride ions within a correct selection when using tooth paste products. A number of research studies suggested that toothpastes with low fluoride concentration (250 ppm) are less effective than toothpastes with the standard 1,000-1,500 ppm of fluoride concentration at preventing caries in permanent teeth. However, toothpaste with the fluoride level of 1,000-1,500 ppm is not suitable for children since it could speed up the enamel fluorosis of the front permanent teeth. This is because most young infants and children under age 02 years can swallow most of the toothpaste while brushing teeth.  Therefore, parents must select pediatric toothpaste which has a low fluoride concentration (< 600 ppm) for their children. 

Effects of Fluoride on our health 

Metabolism in our body
Fluoride is mainly consumed through the oral cavity. The sources of fluoride are fluoridatedwater and fluoride containing dental products. Then it starts to get absorbed by the stomach and  upper  part of the small intestine. In the stomach, the absorption of fluoride depends on the pH of the stomach while in the small intestine fluoride absorption is pH independent and absorption is through facilitated diffusion. Fluoride absorption depends on numerous factors such as stomach pH, the chemical formula of consumed fluoride, presence of food in the stomach, interaction with other minerals in food ingredients present in gastrointestinal tract such as aluminum, calcium, and magnesium compounds. The unabsorbed fluoride is excreted through feces while the absorbed fluoride is distributed rapidly through the circulation into the intracellular and extracellular fluids and is retained only in the mineralized tissues of the body. The fluoride uptake by mineralized tissues is more efficient in growing children and progressively declines with age. Retention of fluoride in the mineralized tissues of the body is reversible. Fluoride is released back slowly when the fluoride level in plasma falls. Absorbed fluoride is deposited from serum into mineralized tissues while the remaining is excreted primarily into the urine and to a lesser extent into feces, sweat, saliva and breast milk. The excretion of fluoride through the urinary system depends upon several factors like plasma levels of fluoride, glomerular filtration rate (GFR), pH of the urine, and its flow. 

Thyroid dysfunction
The frequent use of fluoride interferes in the function of the thyroid gland since it is a halogen which has antagonistic properties toward iodine by preventing the success of iodine treatment of endemic goiter. Fluoride has the ability to increase the concentration of thyroid stimulating hormone (TSH) and decrease the concentration of T3 and T4 hormones by producing hypothyroidism in some people since the thyroid gland is the most sensitive tissue in the body for fluorides. Research studies have discovered that prolonged exposure of high fluoride has potential to suppress the function of the thyroid gland and this will change the level of thyroid hormone. As a result of that, imbalance the oxidation / antioxidation system in our body and eventually it will be a reason to reduction in the learning memory abilities. 

Insulin secretion
Fluoride is a highly toxic to diabetic patients. Therefore, it works as a low-dose endocrine disruptor in people who are affected from high blood sugar. Research studies have explored that insulin resistance in humans is caused by higher exposure of fluoride either from water or other sources such as tooth paste and prepared food stuff.  This phenomena mainly occurs due to increased hepatic glycogenolysis by fluorides. Because, Fluoride ion has the ability to stop Glycolysis by inhibiting enolase which is metalloenzyme involved in lactic acid formation while as a result of that accumulation of 2-phosphoglycerate is occurred. Then it is equilibrated with 3-phosphoglycerate by the enzyme phosphoglucomutase. As a result of this, the glucose level in blood is increased. 

The high use of fluorides lead to higher risk of impaired kidney function, increased capillary permeability, microcirculatory defects and altered protein biosynthesis in the pancreas. On the other hand, chronic Fluoride exposure causes for hypo-thyroidisms which also effects patients with diabetes through the reduction of peripheral glucose metabolism.  
Cell culture studies have evidenced that glucose stimulated insulin secretion is repressed as the fluoride concentration increases.

Reproductive health
Some research studies indicate that high Fluoride exposure is associated with the increased levels of follicle stimulating hormone (FSH) and luteinizing hormone (LH), decreased estrogen levels, decreased testosterone levels and changes in its conversion into its potent metabolites, reduced thyroid hormones, disturbed androgen to estrogen ratios (A/E) and estrogen receptor to androgen receptor ratios (ER/AR). As a result of these changes, problems related to fertility in both male and females occur. The most significant consequences of fluoride exposures in male reproduction are changes in the structure and functional activities of spermatozoa, disruption of spermatogenesis, and instability of multiple hormone systems. Moreover, according to the rat studies, lower pregnancy rate is occurred due to increased fluoride concentration. 

Neuronal Health
Fluoride is a developmental neurotoxin that has been linked to human brain damage including effects on learning and memory. Studies have discovered that Fluoride concentration above 01 mg/L develops neurotoxicity. Fluoride exposure to the developing brain is more vulnerable to damage by toxicants than in case of matured brain and possibly leads to permanent damage to the developing brain. Recent experiments showed that exposure to high concentration of Fluoride does have harmful effects on the mental ability of the children.  According to a meta-analysis performed in China, children who live in Fluoride prevalent areas have five times higher chances of developing a low IQ than those who live in having less Fluoride areas. 

Bone and dental health
Fluorosis is a chronic condition caused by excessive intake of Fluoride compounds marked by mottling of the teeth (spots in teeth) and calcification of the ligaments in chronic exposure. There are two types of fluorosis such as skeletal fluorosis and dental fluorosis. Toxic levels of fluoride in skeletal have been coupled with a weakening of bones and an increase in hip and wrist fractures. Sometimes, early stages of skeletal fluorosis are not clinically apparent and may be misdiagnosed as rheumatoid arthritis. 
Dental fluorosis defined as a hypo-mineralization of tooth enamel caused by intake of too much fluoride during enamel formation. In the extra-cellular environment of maturing enamel, an excess of fluoride ions changes the rate at which enamel matrix proteins (amelogenin) are enzymatically broken down and the rate at which the subsequent breakdown products are removed. Fluoride may also indirectly alter the action of protease via a decrease in the availability of free calcium ions in the mineralization environment. This results in the formation of enamel with less mineralization. It appears as a range of visual changes in enamel and subsequently, degrees of intrinsic tooth discoloration is occurred. In the most common form there are faint white lines or specks, but slightly more severe cases appear as white mottled patches, while severe fluorosis is characterised by brown discoloration and weak, uneven and rough enamel.

Gastrointestinal tract (GIT)
High concentration fluoride chemically reacts with gastric acid (hydrochloric acid) in the stomach to form hydrogen fluoride while gastric mucosa is irritated by this excessive formation of hydrofluoricacid. As a result of that non-ulcer dyspeptic symptoms such as upper abdominal pain have been observed in populations consuming high fluoride concentration.  Some animal studies reveal that fluoride has a potential to stimulate the secretion of gastric acids and diminish blood supply away from the stomach lining. This may result in the death of epithelial cells of gastrointestinal track. 

Fetal defects
Fluoride can crosses the placental barrier and incorporates into the fetal tissues. This may disturb the development of the embryo or fetus.  The genotoxic effects of fluoride are due to an abnormality in chromosomes. Therefore, any accidental ingestion of high amounts of tooth paste which are fortified with higher concentration of fluoride can lead to harmful effects on the fetus. In addition to that, fetal brain is also susceptible to fluoride poisoning and results in remarkable neurological damage, neuronal degeneration, and reduced secretion of neurotransmitters such as norepinephrine. Moreover, fluoride disrupts the secretion of certain neurotransmitters and nerve cell receptors and results in neural dysplasia.

Other effects 
Excessive fluoride ingestion affects multiple body systems with disturbances in respiratory functions, the gastrointestinal system, liver, and excretory system, causes hematological manifestations including red blood cell deformation, neurological manifestations such as depression, abnormal sensations in toes and fingers, excessive thirst, headache, and reduction in immune response.  Chronic fluoride toxicity adversely affects both cell mediated and humoral (body fluid) immunity. For instance, it destroys the white blood cell energy reservoirs that are required for phagocytosis of foreign agents and by inhibition of antibody formation.

Conclusion
Fluoride is safe under a recommended dosage by WHO. While excessive quantities may harm us. Therefore, we have to consider many aspects when selecting toothpaste. We can shift in to herbal tooth paste which does not contain fluoride;  this is because we are getting fluoride adequately via our drinking water. Fluoride is included in the water purification process.
The writer is a medical laboratory technologist at a private hospital and holds a MSc. Degree in Industrial and Environmental Chemistry from the University of Kelaniya and a BSc. Food Production and Technology Management degree from the Wayamba 
University of Sri Lanka.