The fluoride content of a representative diet of the young adult male

Chemical Aspects of Human and Environmental Overload with Fluorine

Over the last 100-120 years, due to the ever-increasing importance of fluorine-containing compounds in modern technology and daily life, the explosive development of the fluorochemical industry led to an enormous increase of emission of fluoride ions into the biosphere. This made it more and more important to understand the biological activities, metabolism, degradation, and possible environmental hazards of such substances. This comprehensive and critical review focuses on the effects of fluoride ions and organofluorine compounds (mainly pharmaceuticals and agrochemicals) on human health and the environment. To give a better overview, various connected topics are also discussed: reasons and trends of the advance of fluorine-containing pharmaceuticals and agrochemicals, metabolism of fluorinated drugs, withdrawn fluorinated drugs, natural sources of organic and inorganic fluorine compounds in the environment (including the biosphere), sources of fluoride intake, and finally biomarkers of fluoride exposure.

Relationship between daily fluoride intake from diet and the use of dentifrice and human plasma fluoride concentrations

The literature contains reports of the relationship between the fluoride concentrations in drinking water and human plasma. None of these studies, however, documented individual levels of daily fluoride intake, which can vary considerably among individuals served by the same water supply. Furthermore, while water can be an important source of fluoride, other sources, especially fluoridated dentifrices, also contribute substantially. This 2-day study with five 25-35-year-old subjects in each of three communities (Bauru, 0.6-0.8 ppm F; Domelia, 0.7 ppm F; Floresta, 0.3 ppm F) determined plasma fluoride concentrations and fluoride intake from diet and the use of dentifrice which, together, approximate total daily fluoride intake. The purposes were to determine: (1) the extent to which plasma fluoride concentrations approached levels known to affect the quality and quantity of bone; (2) the relationship between fluoride intake and plasma concentrations. Plasma was collected at 4-h intervals starting at 0800 h and ending at 2000 h each day. Average fluoride intakes from diet and the use of dentifrice in the three communities ranged from 0.16 to 0.82 mg/day and from 0.29 to 3.16 mg/day, respectively. The overall average plasma concentrations in the three communities were 0.44, 0.45 and 0.54 micromol/l (P<0.005). They were directly related to intake from the use of dentifrice (P=0.030) and to total intake (P=0.033), but were not related to dietary intake (P=0.176). In conclusion, despite fluoride intake from various sources, the plasma fluoride concentrations of the study subjects remained at levels far below those associated with effects on bone production.

The bio-availability of fluoride from black tea

OBJECTIVES

To investigate the oral retention of fluoride from tea and its association with the tooth surface and acquired pellicle.

METHODS

Oral retention of fluoride after rinsing in vivo was assessed from expectorated samples with an ion specific electrode methodology. Interaction of fluoride with the tooth surface and acquired pellicle was examined in situ with enamel blocks mounted on partial removable appliances. In vitro models were used to examine fluoride binding to enamel particles.

RESULTS

Thirty four percent of the fluoride was retained in the oral cavity after rinsing with tea. Differences in retention at the tooth surface in the presence and absence of an acquired pellicle were not statistically significant at incisor or molar sites. Fluoride from tea showed strong binding to enamel particles, which was only partially dissociated by solutions of ionic strength considerably greater than that of saliva. Binding studies demonstrated strong avidity of enamel for tea and salivary pellicle components.

CONCLUSIONS

This study has demonstrated that tea can provide an effective vehicle for fluoride delivery to the oral cavity where it may interact with the oral tissues and their surface integuments. This may lead to local topical effects of the ingested fluoride as well as systemic effects following oral and gastro-intestinal absorption.

Intake and metabolism of fluoride

The purpose of this paper is to discuss the major factors that determine the body burden of inorganic fluoride. Fluoride intake 25 or more years ago was determined mainly by measurement of the concentration of the ion in the drinking water supply. This is not necessarily true today because of ingestion from fluoride-containing dental products, the "halo effect", the consumption of bottled water, and the use of water purification systems in the home. Therefore, the concentration of fluoride in drinking water may not be a reliable indicator of previous intake. Under most conditions, fluoride is rapidly and extensively absorbed from the gastrointestinal tract. The rate of gastric absorption is inversely related to the pH of the gastric contents. Overall absorption is reduced by calcium and certain other cations and by elevated plasma fluoride levels. Fluoride removal from plasma occurs by calcified tissue uptake and urinary excretion. About 99% of the body burden of fluoride is associated with calcified tissues, and most of it is not exchangeable. In general, the clearance of fluoride from plasma by the skeleton is inversely related to the stage of skeletal development. Skeletal uptake, however, can be positive or negative, depending on the level of fluoride intake, hormonal status, and other factors. Dentin fluoride concentrations tend to increase throughout life and appear to be similar to those in bone. Research to determine whether dentin is a reliable biomarker for the body burden of fluoride is recommended. The renal clearance of fluoride is high compared with other halogens. It is directly related to urinary pH. Factors that acidify the urine increase the retention of fluoride and vice versa. The renal clearance of fluoride decreases and tissue levels increase when the glomerular filtration rate is depressed on a chronic basis.

The changing patterns of systemic fluoride intake

Fluorosis prevalence has increased in North America since the 1930's-1940's. It may also have increased since 1970, though the evidence for that is less clear. Continued monitoring will help determine whether increased fluorosis prevalence in children in the United States is a cohort effect from the 1970's. This review considers the evidence for an increase in fluoride ingestion from all sources since the 1970's. If an increase has occurred, the most likely sources are fluoride dietary supplements, inadvertent swallowing of fluoride toothpastes, and increased fluoride in food and beverages. For adults, there is no evidence from dietary surveys to show that fluoride intake has increased over the last generation. Dietary surveys for children aged six months to two years are similarly inconclusive, though the great variation in fluoride content of various infant foods might be obscuring real effects. The data on fluoride intake by children from food and beverages, infant foods included, are not strong enough to conclude that an increase in fluoride ingestion has occurred since the 1970's. However, the suggested upper limit of fluoride intake is substantially being reached in many children by ingestion of fluoride from food and drink (0.2-0.3 mg per day) and from fluoride toothpaste (0.2-0.3 mg per day). Two public health issues that arise from this review are: (a) the need for a downward revision in the schedule for fluoride supplementation, and (b) education on the potential for high fluoride concentration of soft drinks and processed fruit juices.

Trends in the prevalence of dental fluorosis in the United States: a review

This paper assesses, by comparing recent published evidence with Dean's pioneering work, whether an increase in the milder forms of dental fluorosis may have occurred since Dean's time. To the extent that the crude comparisons of recent research with historic studies are valid, the data indicate a slight trend toward more fluorosis today than would be expected based upon findings in the late 1930s and early 1940s. This suggested increase in fluorosis is not as clear-cut nor as widely accepted as the recent decline in the prevalence of dental caries. Thus, further study of the prevalence of fluorosis and caries in relation to fluoride ingestion will be required to help validate the trend, and to allow dental researchers and decision makers to plan for the future.

Dietary fluoride intake of 15-19-year-old male adults residing in the United States

The average daily dietary fluoride intakes of 15-to-19-year-old males were estimated from the analysis of 24 FDA "market basket" food collections made from 1975 to 1982. The data indicate that 15-to-19-year-old males residing in fluoridated (greater than 0.7 ppm) cities had an average daily dietary fluoride intake of 1.85 mg/day when the diet provided an estimated caloric intake of 11.72 megajoules (2800 calories). In non-fluoridated cities, with less than 0.3 ppm in the drinking water, the average dietary fluoride intake was 0.86 mg/day. The beverages and drinking water contributed an average of 75 +/- 2% of the daily dietary fluoride intake.

Fluoride and bone: an unusual hypothesis

Given the total body weight, the weight of the skeleton and the proportion of minerals in the skeleton, a simple formula can be used to estimate the accumulation of fluoride in the skeleton over periods of years. It would appear that daily intakes of fluoride considered beneficial to developing teeth may, if ingested throughout adult life, lead to skeletal fluorosis of varying degrees in a significant proportion of the population. To date, the accumulation of fluoride in the skeleton seems to have been ignored as a possible aetiological factor in certain metabolic bone disorders now common in the middle-aged and elderly. The unusual hypothesis put forward in this paper suggests that a daily intake of fluoride derived from a multiplicity of sources, and which is now generally considered as 'safe', may in fact be potentially harmful over long periods of time.

Dietary intake of fluoride ashed (total fluoride) v. unashed (inorganic fluoride) analysis of individual foods

Fluoride content in ninety-three individual food items from a hospital in a fluoridated area was determined by ashing (total fluoride) v. unashing (inorganic fluoride) analysis. No discrepancy between the two methods was found by food group but two dry cereals and black pepper did show significantly more fluoride after ashing. The reason for the unavailability before ashing was not determined. Daily fluoride intake was estimated at 1.783 mg which is midway between the 1.211 and 2.201 mg reported from studies in which composite diets were analysed. Daily intake from food at 0.4 mg was one-quarter of the daily total intake 1.8 mg; a ratio consistent with those previously reported in serum, urine and bone between residents from a non-fluoridated v. fluoridated community.

Studies of fluoride metabolism in man. A review and report of original data

The dietary intake of fluoride and the fluoride excretions in urine and stool were determined under controlled conditions in man. Fluoride balance studies have shown that the urinary fluoride corresponds to 50--60% of the intake, the fecal fluoride was very low, corresponding to 6% of the intake, and approximately 1 mg fluoride was retained per day during an average fluoride intake of 4.3 mg/day. The fluoride intake depended on the amount of fluoridated water consumed. The dietary fluoride content ranged from 1.2 to 1.5 mg/day. During the intake of supplemental fluoride the fluoride excretions increased but the ratio of the urinary/fecal fluoride was similar. Added fluoride is well retained. Following its discontinuation, very small amounts of the retained fluoride are excreted for several days. Inorganic elements, such as calcium, phosphorus, and magnesium, which have been shown to decrease the intestinal absorption of fluoride in animals were ineffective in man, while aluminum, given as aluminum-containing antacids, markedly decreased the intestinal absorption of fluoride and thereby decreased the retention of fluoride.

Estimated fluoride intake of average two-year-old children in four dietary regions of the United States

Analysis of toddler "Market Basket" food collections indicates that an average two-year-old child living in cities with water supplies containing 0.37 to 1.04 ppm of fluoride has a daily fluoride intake of 0.315 to 0.610 mg/day (0.025 to 0.049 mg/kg body weight) from food, water, and beverages.

Urinary fluoride excretion in small children following short-term fluoride supply with tablets or domestic salt

Urinary fluoride (F) excretion has been studied in small children, with some comparisons with adults, following ingestion of F tablets or fluoridated salt (F-salt) containing 500 mg F/kg NaCl. 24-h urinary F in 7- to 8-year-old children in an institution and in 2- to 12-year-old children in families rapidly increased to average levels of about 0.85 and 0.55 parts/10(6), respectively, when the children had their meals spiced with F-salt. Children in families also showed significantly elevated urinary F excretion with two F-salted meals a day but not with one a day. After taking 0.5 mg F in the form of NaF tablets a group of children without previous F supply attained within 1 d a 24-h urinary F concentration which was about the same as that in children who had been taking caries-preventive tablet doses for years. The percentage of a single F dose excreted in the urine within 4 h after the ingestion of F tablets or an F-salted standard meal was about the same in preschool children and middle-aged adults. F quantities of the order 1.5-2 mg could be ingested by a child eating a meal comprising strongly F-salted dishes, and the urine could reach concentrations around 3 parts/10(6) F during the following 2-4 h. The results obtained support the concept that domestic salt containing about 500 parts/10(6) F is suitable for clinical testing on a larger scale under Swedish conditions. Calculations of F supplies to children aged 2 months-7 years with different diets and water and salt F contents are presented as diagrams.

Renal excretion of fluoride in renal failure and after renal transplantation

We have compared the renal excretion of fluoride in a variety of patients with chronic renal failure maintained with and without protein restriction before and during regular dialysis treatment and after transplantation. The patients tended to continue to excrete normal dietary loads of fluoride quite well until renal function was seriously reduced. From a regression of function on excretion the mean level of creatinine clearance when a normal dietary load of fluoride 0.0526 plus or minus 0.019 mmol/2 h (1.0 plus or minus 0.36 mg/24h) has a 90% chance of being excreted lies around 16 ml/min, a level when most patients with renal failure will be symptomatic. Acute loading of such patients with additional fluoride in the form of sodium fluoride from 40 mg to 60 mg/day showed a twofold to threefold increase of serum fluoride concentrations, slight increases in urinary fluoride excretion, and heavy tissue absorption, suggesting that prior fluoride loading of the skeleton had not taken place. These effects contrasted with those in one patient with normal renal function and with those in one patient with skeletal saturation due to prolonged loading. After renal transplantation fluoride excretion increased but reached normal levels within three months of satisfactory function, suggesting that fluoride loading in renal failure and during regular dialysis therapy had not been excessive.