In contrast to the findings of over 60 animal studies from other research teams, a series of studies by FDA researchers Sprando & Collins reported virtually no evidence of reproductive toxicity among animals treated with very high levels of fluoride exposure. The reasons for this discrepancy remains unclear.
Excerpts from Sprando/Collins’ Studies:
“This study provides quantitative information on the effect of sodium fluoride (NaF) on the testes of F1 generation male rats exposed in utero and during lactation to NaF at one of four concentrations (25, 100, 175, 250 ppm). At weaning, the F1 generation males were exposed to NaF in their drinking water for 14 weeks, after which time testicular tissues were perfusion-fixed with glutaraldehyde and observed after being embedded in plastic. The seminiferous tubules comprised 89%, 87%, 88%, 88% and 88% of the total testis volume while the interstitial space occupied 9.3%, 11.2%, 10.2%, 9.8% and 9.9% of the total testis volume for the 0, 25, 100, 175 and 250 ppm NaF treatment groups, respectively. Statistically significant differences between control and NaF-treated rats were not observed with respect to absolute volume of the seminiferous tubules, interstitial space, Leydig cells, blood vessels boundary layer, lymphatic space, macrophages, tubular lumen or absolute tubular length and absolute tubular surface area, mean Sertoli cell nucleoli number per tubular cross-section, mean seminiferous tubule diameter and the mean height of the seminiferous epithelium. A statistically significant decrease in the absolute volume and volume percent of the lymphatic endothelium was observed in the 175 and 250 ppm NaF-treated groups and in the testicular capsule in the 100 ppm NaF-treated groups. The significance of this finding is unknown at the present time. Overall, the quantitative information obtained suggests that exposure to NaF at the doses used in the present study does not adversely affect testis structure or spermatogenesis in the rat.”
SOURCE: Sprando RL, et al. (1998). Testing the potential of sodium fluoride to affect spermatogenesis: a morphometric study. Food Chem Toxicol. 36(12):1117-24.
“The potential of sodium fluoride (NaF) to affect spermatogenesis and endocrine function was assessed in P and F1 generation malerats. Male and female experimental rats received sodium fluoride in their drinking water at one of four concentrations (25, 100, 175, 250 ppm). P generation male and female rats were exposed to sodium fluoride in their drinking water for 10 wk and then males were mated to females within the same treatment groups. Reproductive tissues were collected from P generation male rats after approximately 14 wk of treatment. Pregnant females (P) were exposed to sodium fluoride via their drinking water through gestation and lactation. F1 generation weanling male rats remained within the same treatment groups as their parents. F1 generation male rats were exposed to sodium fluoride in their drinking water for 14 wk, at which time reproductive tissues were collected. Dose-related effects were not observed within the P and F1 treatment groups in testis weights, prostate/seminal vesicle weights, non-reproductive organ weights, testicular spermatid counts, sperm production per gram of testis per day, sperm production per gram of testis, LH, FSH or serum testosterone concentrations. Histological changes were not observed in testicular tissues from either the P or F1 generation. We conclude that prolonged exposure to sodium fluoride in drinking water at the doses administered in this study does not adversely affect spermatogenesis or endocrine function in the P and F1 generation male rats.”
SOURCE: Sprando RL, et al. (1997). Testing the potential of sodium fluoride to affect spermatogenesis in the rat. Food Chem Toxicol. 35(9):881-90.
“The potential of sodium fluoride to affect spermatogenesis in the rat was assessed by intratesticular injection. Experimental rats’ left testis was injected with sodium fluoride (50, 175 and 250 ppm) in vehicle (0.9% physiological saline); control testes were injected with vehicle. The right testis served as a non-injected control. Testicular tissues collected ‘at’ and ‘distal to’ the injection site and from the non-injected control testes were evaluated microscopically 24 hr and 1, 2 and 3 wk post-injection. Testicular tissues obtained at and distal to the injection site in all fluoride-injected groups resembled tissues collected from corresponding areas in the controls. Seminiferous tubule damage observed in both the vehicle-injected control testes and the fluoride-injected testes but not in the non-injected testes was attributed to injection trauma. Polymorphonuclear leucocyte infiltration was observed 24 hr post injection only at the injection site in the vehicle- and fluoride-injected groups. Leydig cells were unaffected. Leucocyte infiltration with seminiferous tubule damage was not considered to be a fluoride treatment-related effect because it was observed in both vehicle- and fluoride-injected testes. The results demonstrate that the rat is not adversely affected by direct exposure to fluoride at levels 200 times greater than those under normal conditions.”
SOURCE: Sprando RL, et al. (1996). Effect of intratesticular injection of sodium fluoride on spermatogenesis. Food Chem Toxicol. 34(4):377-84.