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The Journal of Nutrition Vol. 128 No. 8 August 1998,
pp. 1392-1400
Oral Health Research Institute, School of Dentistry and * Division of Biostatistics, School of Medicine, Indiana University, Indianapolis, IN 46202
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ABSTRACT |
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Abstract
Introduction
Methods
Results
Discussion
References
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On the basis of observations that endemic fluorosis occurs more often in malnourished populations, a series of studies tested the hypothesis that deficient dietary intake of calcium, protein or energy affects fluoride metabolism so that the margin of safe fluoride exposure may be reduced. The objective of the investigation was to determine whether changes in fluoride metabolism in nutritionally deficient rats resulted in manifestation of any extraskeletal toxic fluoride effects not observed in healthy animals. This investigation included two studies, one that monitored the effect of calcium deficiency on the effects of chronic fluoride exposure, and a second study that observed fluoride effects in rats that were deficient either in protein or in energy and total nutrient intake. Control and experimental rats received drinking water containing 0, 0.26 (5), 0.79 (15) or 2.63 (50) mmol fluoride/L (mg/L) for 16 or 48 wk. Control rats were fed optimal diets and experimental rats were fed diets deficient in calcium (Study 1) or protein (Study 2). An additional group of experimental rats (Study 2) was provided with a restricted amount of diet; thus these rats were deficient in energy and total nutrient intake. The intake, excretion and retention of fluoride were monitored; after the rats were killed, tissue fluoride levels and biochemical markers of tissue function were analyzed. Bone marrow cells were harvested from some of the rats, after 48 wk of treatment, for determining the frequency of sister chromatid exchange, a marker of genetic damage. Although there were significant differences among fluoride treatment groups in fluoride excretion and retention that resulted in significantly greater fluoride levels in tissues of the experimental rats, we were unable to detect any harmful, extraskeletal biochemical, physiologic or genetic effects of fluoride in the nutritionally deficient rats.
KEY WORDS: fluoride · calcium deficiency · protein deficiency · malnutrition · rats
Fluoride is widely used for reducing dental decay (Dean 1942 Because the incidence of dental and skeletal fluorosis, which are manifestations of the adverse effects of large amounts of fluoride on mineralized tissues, is frequently high in areas of the world where endemic nutritional deficiencies exist, malnutrition may be a predisposing factor in the occurrence of fluorosis (Manji et al. 1986 The types of deficiencies most common in undernourished populations include inadequate intake of protein, vitamins, energy and minerals, particularly calcium. The contribution of these different nutritional deficiencies to fluoride toxicity is unclear. Moudgil and co-workers (1986) observed that the diets of patients with crippling skeletal fluorosis were deficient in calcium. More recently, investigators in India reported that a group of patients with skeletal fluorosis had significantly lower dietary intake of calcium than did those with normal radiological findings (Mithal et al. 1993 Results are also contradictory concerning the effect of protein on individual responses to chronic fluoride exposure. Ekstrand et al. (1982) Adverse skeletal effects resulting from chronic exposure of medically or nutritionally compromised rats to high doses of fluoride have been reported (Turner et al. 1995 This investigation included two studies as follows: one study monitored chronic fluoride exposure in calcium deficient rats (Table 1, Study 1); a second study observed the effects of fluoride on rats that were deficient in either protein or in energy and total nutrient intake (Table 1, Study 2). In both studies, control and experimental male Sprague-Dawley rats (Harlan Sprague Dawley, Indianapolis, IN) were given drinking water containing 0, 0.26 (5), 0.79 (15) or 2.63 (50) mmol fluoride/L (mg fluoride/L), supplemented as sodium fluoride (NaF), for 16 or 48 wk. The rats were received as weanlings (30-40 g) and were assigned to 24 groups (16-20 rats/group) balanced on the basis of initial body weight. From the time of receipt until termination of the study, the rats were fed their assigned diets, all of which were low in fluoride (F < 6.3 µmoL/kg), and their designated drinking water for either 16 or 48 wk. Because of the large number of rats in these studies, both were divided into four phases with the rats in each phase being received at monthly intervals and distributed evenly across all treatment groups. Before beginning the investigation, protocols for both studies were reviewed and approved by the Indiana University School of Dentistry (IUSD)5 Animal Care and Use Committee. The laboratory rats were housed individually in an American Association for Accreditation of Laboratory Animal Care-accredited research facility, and all care and treatment procedures were conducted in compliance with guidelines established by the NIH, the Food and Drug Administration and the USDA.
Diets.
Diets fed to the rats in Studies 1 and 2 are described in Tables 2 and 3, respectively. All diets were prepared in the IUSD Bioresearch Facility, and each batch of diet was analyzed for fluoride before use. Except in the case of the malnourished energy-deficient rats that received a restricted amount of diet in Study 2, all rats were given free access to their assigned diet. Rats in the total nutrient and energy-deficient group in Study 2 were fed only 10 g of the 20% protein diet/d.
Treatment.
All rats were given free access to fluoride as administered in their drinking water. Drinking water was prepared by dissolving NaF in deionized water, and all water was analyzed for fluoride before use. To be accepted for use in the studies, all prepared water samples had to be within ±1.0 mg/L of their designated fluoride concentration. In addition, water samples from individual water bottles were randomly tested during both studies to verify that the rats had received their assigned treatments.
Metabolic periods.
For 4 d immediately before each scheduled termination, 12 rats from each treatment group were housed individually in metabolism cages (Nalgene #650-0350, Fischer Scientific, Cincinnati, OH). During these periods, water and food consumption and total urine volume were recorded. Some of the urine and all of the fecal output from every rat were saved each day for determination of fluoride content. Aliquots of the final 24-h urine samples were also saved for urea and creatinine (CR) analyses.
Study termination.
In both studies, rats in half of the groups were killed after 16 wk of treatment; the remaining groups were killed after 48 wk. Because blood was to be drawn for clinical chemistry analyses, food was withheld from all rats for 12-16 h before termination to allow determination of monitored clinical variables, as well as their comparison, under standard conditions. Before they were killed, rats were anesthetized with ketamine (10 mL of 100 g/L) and xylazine (5.5 mL of 20 g/L) mixed in a 9:1 ratio and injected intramuscularly (1.4 mL/kg body weight). The rats were killed in random order. Blood was drawn by cardiac puncture, and death was then assured by bilateral pneumothorax. Blood, liver, the kidneys, one femur and a section of the lumbar vertebra (L2-L4) were obtained from each rat and saved for fluoride analyses along with carcasses from randomly selected rats (n = 10-12/group). Blood from each rat was also saved for clinical chemistry analyses.
Analytical procedures
INTRODUCTION
Abstract
Introduction
Methods
Results
Discussion
References
); when it is added to drinking water at a concentration of ~0.05 mmol/L (1.0 mg/L), it has no adverse effects (NRC 1993). However, because of its beneficial cariostatic properties, fluoride is now being added to a variety of dental care products, and its increasingly widespread use has renewed consideration of the margin that exists between safe and toxic levels of fluoride exposure (Ekstrand et al. 1990, Smith 1985). There may be cause for concern, particularly in situations in which the metabolism of fluoride is altered by compromised physiologic function or disease.
, Massler and Schour 1952, Moudgil et al. 1986, Murray and Wilson 1948). In a recent study, malnutrition as well as water fluoride levels, was found to have a significant effect on the prevalence of enamel defects in the permanent teeth of Saudi-Arabian children (Rugg-Gunn et al. 1997).
). Results from animal studies are inconclusive. In an early study, Weddle and Muhler (1954) reported that when calcium was intubated along with fluoride, there was a reduction in rat femur fluoride compared with that of rats that received fluoride without calcium. These results were supported by a later investigation (Stookey et al. 1964) which found that fluoride absorption was significantly decreased when calcium was administered along with fluoride. Harrison and co-workers (1984) observed that toxic skeletal effects of fluoride in rats were reduced when dietary calcium was increased, an effect they attributed at least in part to decreased fluoride absorption.
reasoned that because a protein-rich diet lowers urine pH, which promotes the reabsorption of fluoride in the kidney, a low protein diet would result in less acidic urine, a subsequent increase in fluoride excretion and decreased fluoride retention. This theory was supported by earlier investigators (Reddy and Srikantia 1971) who reported that fluoride-treated monkeys maintained on a protein-deficient diet had 25% lower skeletal fluoride values than controls that received adequate protein. From their study, however, Boyde and Cerklewski (1987) concluded that a high protein diet increased urinary fluoride excretion and reduced fluoride retention; other investigators found higher tissue fluoride concentrations and greater enamel defects in protein-deficient than in adequately nourished rats (Likimani et al. 1992, Menaker et al. 1977, Van Rensburg 1972). Mithal and colleagues (1993) found that among individuals exposed to high concentrations of fluoride (7-10 mg/L, 0.37-0.53 mmol/L) in their drinking water, those who developed osteopenia reported lower dietary protein intake; however, Moudgil et al. (1986) concluded that the diets of patients with crippling skeletal fluorosis were adequate in protein but deficient in energy.
, 1996a and 1996b). The aim of this investigation was to determine whether fluoride causes adverse, extraskeletal effects in nutritionally deficient rats. This investigation was based on the hypothesis that if extraskeletal, toxic effects of chronic fluoride exposure occur, nutritionally compromised individuals will be more susceptible to these effects, and detrimental effects of fluoride that are not ordinarily observed in healthy populations may manifest themselves in those with poor nutrition. Inadequate nutrition may lead to physiologic conditions under which the biological effect of fluoride increases and the threshold of safe fluoride exposure decreases. The objectives of the two studies in this investigation were to monitor the effects of chronic fluoride exposure on a number of variables in rats fed diets deficient in calcium, protein or total nutrient and energy intake, and to determine whether changes in these variables were caused by, or reflected adverse physiologic, biochemical or genetic effects of fluoride. The effects of fluoride on the skeletal tissues of the rats in these studies were determined in an ancillary investigation and will be described in a separate publication.
MATERIALS AND METHODS
Abstract
Introduction
Methods
Results
Discussion
References
View this table:
Table 1.
Design of studies
View this table:
Table 2.
Composition of diets in the calcium study (Study 1)
View this table:
Table 3.
Composition of diets in the protein and restricted energy and total nutrient study1 (Study 2)
) and no metabolic, fluoride or clinical chemistry data were obtained from these rats. Twenty-four hours before termination, these rats were anesthetized with the ketamine-xylazine mixture, and two 5-bromo-2'-desoxyuridine (Sigma Chemical, St Louis, MO) tablets (50-60 mg) were implanted subcutaneously in their lateral abdominal region. In each study, two of the rats that had received no fluoride and had been fed the control diet were given 10 mg/kg of the known mutagen cyclophosphamide (Sigma Chemical) intraperitoneally, 16 h before killing and served as positive controls. All rats were treated with 0.6 mg colchicine/kg intraperitoneally 2 h before killing to arrest cell division. At the time they were killed, each rat was anesthetized again with ketamine-xylazine; both femurs were removed, and the marrow cells were harvested for scoring the frequency of SCE. Death was assured by bilateral pneumothorax.
Fluoride analyses.
Blood samples were centrifuged at 3500 × g for 15 min at 4°C immediately upon collection, and plasma was saved for fluoride analysis. Fluoride was measured in a centrifuged aliquot of each urine sample after the total sample volume was recorded. Feces and soft tissues were homogenized in known amounts of deionized water before analyses, and mineralized tissues were ashed (600oC), weighed and pulverized before analysis of ~10 mg of each ashed sample for fluoride. Drinking water used for treatment was diluted 1:1 with Total Ionic Strength Buffer and analyzed directly for fluoride by using a combination fluoride ion-specific electrode (Orion No. 96-09-00) and a pH/ion meter (Accumet 950, Fischer Scientific). Fluoride analyses of all diets and biological samples were conducted using a modification of the hexamethyldisiloxane (HMDS: Sigma Chemical), acid diffusion procedure (Dunipace et al. 1995, Taves 1968). Quality assurance procedures were conducted periodically during both studies to validate analytical data, and the coefficient of reliability was >95% in our laboratory.
Clinical chemistry analyses. Plasma and urine biochemical markers of tissue function were analyzed using autoanalyzers located in the Department of Pathology, Wishard Memorial Hospital (Indianapolis, IN). A VITROS 750 XRC random access chemical analyzer (Johnson and Johnson, Rochester, NY) was used to analyze plasma variables, analyzing electrolytes by ion selective technology and blood urea nitrogen by colorimetric methodologies. Urine variables were analyzed by using a Dimension clinical chemistry analyzer (Dade, Wilmington, DE). Monitored plasma components included the following: urea, glucose, CR, calcium, phosphorus, uric acid, cholesterol, total protein, albumin, total bilirubin, alkaline phosphatase (EC 3.6.11) and aspartate aminotransferase (EC 2.6.1.21). Urine urea and CR were also analyzed, and CR clearance was calculated as follows: clearance (mL/min) = [urine flow (mL/min) × urine CR (g/L)]/plasma CR (g/L).
Bone marrow sister chromatid exchange (SCE).
The procedures for harvesting and fixing the femur bone marrow cells have been described previously (Li et al. 1987, Perry and Thomson 1984). After fixation, 25 metaphase stage 2 (M2) cells from each animal were examined for their frequency of SCE.
Statistical analyses.
All data have been expressed as means ± SEM, and the level of significance for all statistical tests in these studies was set at 
= 0.05. A three-factor full factorial ANOVA model was used to analyze the effects of diet, fluoride treatment and duration, as well as their interactions, on outcome measures. When significant effects were detected, Tukey's multiple comparison adjustment was used for making multiple mean comparisons. The natural logarithm of all fluoride data was taken before analysis to correct for the nonhomogeneity of variances among fluoride treatment levels. SCE results were analyzed by two-way ANOVA to investigate the effects of diet, treatment and their interaction. The SAS statistical software program, version 6.11, was used to conduct all analyses (SAS Institute, Cary, NC).
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RESULTS |
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Abstract
Introduction
Methods
Results
Discussion
References
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Although duration of treatment had an effect on most of the variables monitored in this investigation (as referenced below), there were no three-way interactions among nutritional status, fluoride treatment and treatment duration in either study. This means that after 48 wk of treatment, the interaction of fluoride with nutrition was not different from that seen after 16 wk. Therefore, although duration was included in all analyses, the 16- and 48-wk data have been combined for presentation in the figures.
Study 1: calcium deficiency
Growth. Overall, the level of dietary calcium had a significant effect on animal growth. There were no significant differences in initial body weight (mean ± SEM: 63.8 ± 0.23 g) among any of the treatment groups. Body weight gain of rats given 0.125% dietary calcium was significantly less (380 ± 6 g) than that of the rats fed diets containing 0.25% (399 ± 7 g) or 0.5% calcium (411 ± 6 g). There were no significant differences in weight gain among any of the nutritional groups exposed to 0, 5 or 15 mg fluoride/L; however, rats given 0.125% dietary calcium and treated with 50 mg fluoride/L gained significantly less weight than comparably treated rats fed the calcium-replete or optimal diets.
Metabolic variables. There were no significant differences among any of the nutritional groups in mean food or water intake or in urine volume. Dietary calcium level and fluoride treatment both had a significant effect on urine and fecal fluoride excretion and on fluoride retention; these results are summarized in Figure 1 where, within each fluoride treatment group, means designated with different letters are significantly different (P < 0.05). There were significant fluoride dose-related differences in all monitored metabolic variables. Average daily fluoride intake was not affected by dietary calcium level (Fig. 1A). At all fluoride treatment levels, fecal fluoride excretion decreased significantly as dietary calcium was reduced (Fig. 1B). Overall, the calcium-deficient rats tended (P < 0.01) to excrete more fluoride in their urine (Fig. 1C); when they were exposed to the higher concentrations of fluoride (15 and 50 mg/L), the calcium-deficient rats retained significantly greater amounts of fluoride (Fig. 1D).
Tissue fluoride. Figure 2 presents tissue fluoride concentrations for representative soft and mineralized tissues. The relationship of tissue fluoride levels in the three nutritional groups was the same in all monitored tissues. Among all treatment groups, there were significant fluoride dose-related increases in plasma and tissue fluoride concentrations in each nutritional class. ANOVA indicated that, overall, tissue fluoride levels increased significantly as dietary calcium was reduced. Multiple mean comparisons showed that, within most of the fluoride treatment groups, tissue fluoride concentrations were significantly higher in the rats fed 0.25 and 0.125% calcium than in the rats that received the diet containing optimal calcium. Treatment duration was also a significant factor, with most tissue fluoride levels, particularly those of the mineralized tissues, increasing between 16 and 48 wk.
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Clinical variables. Table 4 summarizes the clinical variables in rats consuming diets containing different amounts of calcium. Glucose, blood CR, uric acid, cholesterol, total bilirubin and aspartate aminotransferase as well as urine CR, urea and CR clearance were not affected by nutritional status or fluoride treatment. Dietary calcium level affected blood urea nitrogen (BUN) and calcium concentration. BUN levels were significantly greater in the calcium-deficient rats, and their blood calcium was significantly lower. Although ANOVA indicated that alkaline phosphatase levels were affected by the rats' calcium intake, subsequent multiple mean analysis indicated a significant difference in this blood enzyme level only between rats fed the 0.125 and 0.250% calcium diets and not between those fed the 0.125 and 0.5% calcium diets. Blood BUN, calcium and alkaline phosphatase levels were not significantly affected by fluoride. Overall, ANOVA indicated that fluoride treatment had a significant effect on blood albumin, phosphorus and total protein levels; however, here again, subsequent multiple mean analyses failed to find significant dose-response effects. There were no interactions of nutrition and fluoride in the case of any of the monitored blood or urine components. Although treatment duration had a significant effect on some of the monitored clinical variables, there were no nutrition-fluoride-duration interactions.
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SCE. In Study 1, the mean frequency of SCE ranged from 2.0 ± 0.2 SCE/cell for the 0.5% calcium group treated with 15 mg fluoride/L to 2.5 ± 0.1 SCE/cell for the 0.125% calcium-fed rats exposed to 5 mg fluoride/L. None of the values were significantly different from those of the negative control rats that were fed the optimal diet and given no fluoride (2.2 ± 0.1 SCE/cell). Neither nutritional status nor fluoride had a significant effect on SCE frequency in this study. Positive control, cyclophosphamide-treated rats had 41.3 ±0.2 SCE/cell, thereby validating the methodology.
Study 2: restricted protein and energy intake
Growth. Mean initial body weight (59.2 ± 0.23 g) did not differ significantly among the rat groups in this study. Nutritional status, particularly restricted energy intake, had a significant effect on the growth of rats. However, fluoride treatment had no significant effect, and there were no interactions of nutrition and fluoride. When data for comparable 16- and 48-wk treatment groups were combined, weight gain ranged from 404 ± 12 to 420 ± 13 g for rats fed the control, 20% protein diet; from 382 ± 15 to 389 ± 14 g for rats fed replete (10%) protein; and from 153 ± 5 to 168 ± 7 g for the malnourished rats that received a restricted amount of diet.
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Metabolic variables. Metabolic variables monitored for the rats in this study are summarized in Figure 3. ANOVA indicated significant nutrition and fluoride effects and also a significant interaction of these factors on most of the metabolic variables. Daily fluoride ingestion (data not shown) did not differ among comparably treated groups given the 20 and 10% protein diets. Among the rats that received nonfluoridated water, and for which fluoride was derived totally from the diet, those restricted in energy consumed significantly less fluoride. However, when fluoride intake was expressed on the basis of body weight (Fig. 3A), the malnourished rats consumed significantly greater amounts of fluoride, and the difference became more marked with increasing fluoride treatment. Fecal fluoride excretion of the malnourished, energy-deficient rats was significantly lower than that of comparably treated rats in the other two nutrition groups (Fig. 3B); overall, rats fed the 10% protein diet excreted less fluoride in their urine (Fig. 3C). Fluoride retention was directly proportional to fluoride exposure and also increased as a function of nutritional deficiency (Fig. 3D). Adjusted fluoride intake [mg F/(kg·d)] decreased as the rats aged. Urinary fluoride excretion increased between 16 and 48 wk, whereas fecal fluoride and fluoride retention decreased significantly with age.
Tissue fluoride. Figure 4 summarizes the results of the fluoride analyses conducted on some of the tissues from rats in Study 2. Other analyzed tissues showed the same patterns of fluoride distribution. There were significant dose-related differences in fluoride levels in plasma and all monitored tissues within each nutritional group. Overall, nutritional status was also a significant factor, with tissue fluoride levels increasing as nutritional deficiency increased. For the liver and plasma (Fig. 4A), however, multiple mean comparisons found no significant effect of nutritional status on fluoride levels within individual treatment groups. Rats that were fed the optimal, 20% protein diet had significantly lower concentrations of fluoride in their kidneys than did rats in the two nutritionally compromised groups (Fig. 4B). In the case of the mineralized femur, vertebra (Fig. 4C) and carcass, the mg fluoride/g tissue ash was significantly greater in the energy-restricted rats than in other comparably treated rats. However, in terms of total tissue fluoride, the femur (Fig. 4D) and carcass tissues from energy-compromised rats exposed to 50 mg fluoride/L contained significantly less fluoride than the same tissues from rats that received comparable treatment but were fed the optimal (control) and replete protein diets. Except for the liver, treatment duration had a significant effect on increasing tissue fluoride levels. As in Study 1, however, there were no nutrition-fluoride-duration interactions.
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Clinical variables. Data for the clinical variables of rats in Study 2 are summarized in Table 5. Fluoride treatment had no significant effect on any of the clinical blood or urine components monitored in this study, nor were there any significant fluoride-nutrition interactions. ANOVA indicated that nutritional status significantly affected all monitored variables except for blood phosphorus and total bilirubin levels. However, multiple mean analyses revealed no significant differences in blood aspartate aminotransferase and uric acid levels or in CR clearance among the rats within each treatment group. In general, clinical chemistry data did not differ between rats fed the 10 and 20% protein diets but there were significant differences between these groups and the energy-compromised rats. The energy-restricted rats had lower blood calcium, cholesterol, glucose, total protein and blood and urine CR values, whereas their alkaline phosphatase and normalized CR clearance [µL/(min·g body weight)] results were higher. Although many of the clinical variables changed significantly as treatment duration increased, there were no nutrition-fluoride-duration interactions.
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SCE. The frequency of SCE for the rats in Study 2 ranged from 2.1 ± 0.1/cell for the negative control rats that were fed the optimal diet and received no fluoride treatment to 2.8 ± 0.2/cell for the energy-compromised rats treated with nonfluoridated water. The methodology in this study was also verified by a significant increase in SCE frequency in the positive control, cyclophophamide-treated rats (45.9 ± 0.5/cell). Nutritional status significantly affected SCE in this study, with the malnourished, energy-restricted rats having a higher frequency of SCE (2.61 ± 0.10/cell) than the rats in the 20% protein (2.21 ± 0.05/cell) and 10% protein (2.29 ± 0.06/cell) groups; however, fluoride was not a significant factor.
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DISCUSSION |
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Abstract
Introduction
Methods
Results
Discussion
References
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The hypothesis tested in this investigation was that nutritionally compromised individuals may be susceptible to toxic effects of chronic fluoride exposure that do not manifest in healthy individuals. These studies were conducted to determine whether rats fed diets deficient in calcium, in protein or in energy and total nutrient intake experienced adverse, extraskeletal physiologic, biochemical or genetic effects as a result of chronic fluoride exposure. The fluoride treatments chosen for these studies were based upon previous observations that, for any given level of fluoride exposure, plasma ionized fluoride concentrations tend to be lower in the rat model than in humans. Although ingestion of drinking water that contains 2.0 mg fluoride/L (0.11 mmol/L) results in human plasma fluoride levels between 0.5 and 2.1 µmol/L (Guy et al. 1976), water fluoride concentration must be increased four to five times, to 8-10 mg/L (0.42-0.53 mmol/L), to achieve comparable plasma fluoride in rats (Angmar Mansson and Whitford 1982, Dunipace et al. 1995). Therefore, the concentrations of fluoride tested in these studies were estimated to result in plasma fluoride levels in the optimally nourished, control rats equivalent to those in humans who ingest water fluoridated at ~1.0 mg/L (0.05 mmol/L), 3.0 mg/L (0.16 mmol/L) or 10.0 mg/L (0.53 mmol/L).
, Whitford 1994). Urinary fluoride excretion (mg/L) was also inversely related to dietary calcium. However, when these data were combined for the three fluoride-treated groups within each nutritional class and urine fluoride excretion was expressed as a percentage of the absorbed fluoride, the calcium-deficient rats excreted a lower percentage of bioavailable fluoride (58.6 ± 1.6%) in their urine than did those fed the calcium replete (62.0 ± 1.7%) or the optimal calcium diet (68.0 ± 2.1%). The increase in urinary fluoride excretion did not compensate for its increased absorption with the net result that fluoride retention and tissue fluoride levels were also inversely related to dietary calcium levels.
reported significant, direct relationships between dietary protein concentration and fluoride absorption as well as urine fluoride. The fact that our study detected only numerical differences in these variables between rats fed the two different protein diets may be due to the smaller difference in protein concentrations of the diets tested in this study (10 vs. 20%) compared with those tested by Boyde and Cerklewski (12 vs. 36%). Urine pH was not monitored in the current investigation. Urine fluoride data obtained in Study 2, as well as the results previously reported by Boyde and Cerklewski (1987), appeared to contradict the hypothesis of Ekstrand and co-workers (1982) that a high protein diet, because of a resulting fall in urinary pH, would result in enhanced reabsorption of fluoride by the kidney and reduced urinary fluoride excretion. However, a high protein diet was not included in the current study; thus direct comparison with the investigation by Ekstrand et al. (1982) is not feasible. In all monitored tissues except the kidney, fluoride levels did not differ in rats fed the 20 and 10% protein diets. One exception occurred in the case of the rats that were given 10% protein and drinking water fluoridated at 50 mg/L: these rats retained significantly more fluoride in their kidneys than comparably treated rats fed the optimal-protein diet.
). Data from both studies in this investigation indicated that chronic exposure to concentrations of fluoride as high as 50 mg/L (2.63 mmol/L) had no effect on the frequency of bone marrow SCE in either the control or nutritionally compromised rats. Rats nutritionally deficient in calcium, in protein or in energy and total nutrients were not at increased risk of experiencing genotoxic effects even though they retained significantly greater amounts of fluoride.
, Manji et al. 1986, Massler and Schour 1952, Mithal et al. 1993, Moudgil et al. 1986, Murray and Wilson 1948, Rugg-Gunn et al. 1997). Although the results of animal studies must be applied with caution to human populations, this investigation was unable to identify any harmful extraskeletal, biochemical, physiologic or genetic effects of fluoride in nutritionally deficient rats. The results of this investigation agree with those of our earlier studies (Dunipace et al. 1995, 1996 and 1998), which found that although chronic exposure to large amounts of fluoride may alter mineralized tissues of the body, fluoride, under a variety of medically compromised conditions in which its metabolism is altered and its tissue levels are dramatically increased, has no harmful effects on other tissues of the body.
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FOOTNOTES |
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Manuscript received 9 February 1998. Initial reviews completed 16 March 1998. Revision accepted 16 April 1998.
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ACKNOWLEDGMENTS |
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The authors acknowledge the contribution made by the Directors and staff of the Bioresearch Facility at the Indiana University School of Dentistry who cared for and treated the animals in this investigation. The authors thank Kenneth W. Ryder, Professor of Pathology, Indiana University School of Medicine, and his staff for conducting the clinical chemistry analyses and are also grateful to Juan M. Navia, Professor Emeritus, at the University of Alabama at Birmingham for his review and critique of this manuscript.
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LITERATURE CITED |
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Abstract
Introduction
Methods
Results
Discussion
References
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