Insulin is a hormone produced by the pancreas that is responsible for maintaining appropriate levels of glucose in the blood. Insulin allows the body’s cells to take up glucose from the blood, and either use it as an energy source or store it as glycogen. Blood glucose levels in diabetics are not properly regulated, either because the pancreas does not produce adequate amounts of insulin (i.e., type 1 diabetes mellitus), or because the body’s cells have become less responsive to insulin that is produced (“insulin resistance”; i.e., type 2 diabetes mellitus). Studies on both animals and humans have revealed a transient inhibition of insulin secretion following fluoride ingestion, resulting in hyperglycemia (elevated blood sugar). Fluoride may also lead to increased insulin resistance, or decreased insulin sensitivity, thus contributing to glucose intolerance.

Studies Finding Fluoride Inhibits Insulin Secretion

“[W]hen cells were exposed to F- and challenged with the stimulatory glucose concentration, at 1.35 and 2.26 mM F-, insulin secretion decreased by approximately 20% compared to the control group.”
SOURCE: Garcia-Montalvo EA, et al. (2009). Fluoride exposure impairs glucose tolerance via decreased insulin expression and oxidative stress. Toxicology 263: 75-83.

“Sodium fluoride 5-20 umol/L in the extracellular space inhibited insulin secretion by isolated Langerhans Islets stimulated with glucose.”
SOURCE: Menoyo I, et al. (2008). Fluoride-induced resistance to insulin in the rat. Fluoride 41(4): 260-9.

“The blood-insulin and the C-peptide in the exposed group were lower than those in the control group.”
SOURCE: Xie YP, et al. (2000). Clinical study of the effect of high fluoride on the function of the pancreatic islet b-cells. Chinese Journal of Endemiology 19(2): 84-6.

“The Area Under the Curve of insulin during a standard glucose tolerance test showed an inverse relationship with fluoremia [blood fluoride level]. This observation coincides with experiments published elsewhere indicating that fluoride intake at concentrations 5 microM or greater, inhibits the secretion of insulin.”
SOURCE: de la Sota M. (1997). [Changes in bone mass and glucose homeostasis in subjects with high spontaneous fluoride intake] (Article in Spanish). Medicina 57(4): 417-20.

“The basal and glucose-stimulated insulin secretion of isolated Langerhans rat islets (incubated with solutions containing 2, 5, 10 and 20 umol/l NaF) was significantly inhibited by 5 to 20 umol/l fluoride.”
SOURCE: Rigalli A, et al. (1995). Comparative study of the effect of sodium fluoride and sodium monofluorophosphate on glucose homeostasis in the rat. Drug Res 45(3):289-92.

“[T]he analysis of the results obtained and secondary data allow us to conclude that the pancreas is not unaffected during CFI. For the first time we have provided a complex characteristic of insulin, G and C-peptide contents in the blood serum of people during CFI [chronic fluoride intoxication], which evidenced moderate hypoinsulinemia accompanied by normal or slightly elevated G and glucose levels. Hormonal status changes reflect the complex mechanism of direct or indirect fluoride impact on the production and metabolism of insular hormones. The dynamic of lowering insulin concentration in the blood of fluorosis patients, depending on the intoxication stage, accompanied by a tendency for hypoglycemia, requires more detailed attention, since modern interpretations dictate that absolute or relative insulin deficiency determines the development of diabetes mellitus, triggers disruptions in carbohydrate, fat and protein exchanges and liver function. Further clinical lab and hormonal studies should more fully evaluate the role of the pancreas in CFI pathogenesis and of fluoride as a diabetes-inducing factor.”
SOURCE: Tokar VI, et al. (1992). [Chronic effect of fluorides on the status of the pancreatic insular apparatus of workers]. [Article translated from Russian to English by FAN] Gig Sanit. Nov-Dec;(11-12):42-4.

“One hour after the intake of 60 mg of NaF, fasting human volunteers showed increased fluoride (5-15 uM) together with a significant fall of plasma insulin levels.”
SOURCE: Rigalli A, et al. (1990). Inhibitory effect of fluoride on the secretion of insulin. Calcif Tissue Int 46:333-8.

“The oral administration of sodium fluoride (NaF) (40 umol/100 g body weight) to fasting rats produced an immediate fall in insulin levels and the consequent increase in glycemia. These phenomena were observed with plasma fluoride concentrations 5-15 uM.”
SOURCE: Rigalli A, et al. (1990). Inhibitory effect of fluoride on the secretion of insulin. Calcif Tissue Int 46:333-8.

“There was a significant increase in serum glucose (120% increase), and serum fluoride (10 to 700 fold) 30 min after the injection of NaF. The serum insulin levels were also significantly reduced 30 min after injection of NaF. The insulin levels were 60%, 66%, 75% and 45% of the control values after injection of 0.5, 1.5, 5, and 20 mg F/kg. The data for the first time showed that acute administration of fluoride may inhibit insulin release in 24 hr fasted rats as reflected by significantly lower serum insulin level. It is concluded that the NaF induced hyperglycemia could be due in part to the reduction of serum insulin which would decrease the uptake of glucose by muscle and adipose. It should be noted that the lowest dose of NaF (0.5 mg/kg) is in the range of fluoride ingestion observed following a topical application of APF gel. Thus it is conceivable that normal ingestion of F following an APF application could alter several metabolic processes.”
SOURCE: Shahed AR, et al. (1986). Effect of F on rat serum insulin levels in vivo. Journal of Dental Research 65:756.

Studies Finding Fluoride Increases Insulin Resistance and/or Decreases Insulin Sensitivity

“Based on the present results, we can conclude that chronic treatment with NaF promoted…a decrease in insulin sensitivity.”
SOURCE: Chiba FY, et al. (2012). NaF treatment increases TNF-a and resistin concentrations and reduces insulin signal in rats. J Fluorine Chemistry 136: 3-7.

“It is concluded that the consumption of fluoridated water from water supply did not affect plasma glucose levels even in cases of animals with renal disease. However, a resistance to insulin action was demonstrated. The consumption of water with safe levels of fluoride used in the prevention of dental decay could reduce the stores of insulin. This long-term effect should be studied both in experimental animals and human beings.”
SOURCE: Lupo M, Buzalaf MAR. (2011). Effect of fluoridated water on plasma insulin levels and glucose homeostasis in rats with renal deficiency. Biol Trace Elem Res 140: 198-207.

“The HOMA-IR index [index of insulin resistance] was significantly (p<0.05) higher in the F-treated group than in the control group.”
SOURCE: Chiba FY, et al. (2010). Insulin signal decrease in muscle but not in the liver of castrated male rats from chronic exposure to fluoride. Fluoride 43(1): 25-30.

“The concentration of glucose that produced 50% of the insulin response was significantly higher in rats treated with NaF (6.3+0.2 g/L) compared with the control group (4.3+0.4 g/L), P<0.05. These results indicate that F-treated rats exhibit a significantly reduced sensitivity to glucose stimulus.”
SOURCE: Menoyo I, et al. (2005). Effect of fluoride on the secretion of insulin in the rat. Drug Res 55(5):455-60.