Background─ The relationship between intake of fluoride (F) from drinking water and blood pressure has not been reported. We examined relationship of F in ground water resources (GWRs) of Iran with blood pressure of Iranian population in an ecologic study.
Methods and Results─ Mean F data of GWRs (as a surrogate for F level in drinking water) were derived from a previously conducted study. Hypertension prevalence and mean of systolic and diastolic blood pressure (SBP & DBP) of Iranian population by different provinces and gender were also derived from provincial report of non-communicable diseases risk factors surveillance of Iran. Statistically significant positive correlation were found between ln of mean concentration of F in GWRs and hypertension prevalence of males (r= 0.48, p= 0.007, a= 21.46, b= 4.52), females (r=0.36, p=0.048, a= 19.38, b= 2.34), and overall (r=0.495, p=0.005, a= 20.42, b= 3.43). Also, significant positive correlation between ln of mean concentration of F in GWRs and mean SBP of males (r=0.431, p=0.018, a= 125.13, b= 2.69), and females (r=0.352, p=0.057, a= 118.82, b= 2.78) were found, although the latter was not statistically significant.
Conclusions─ In conclusion, we found increased hypertension prevalence and SBP mean with the increase of F level in GWRs of Iranian population.
Key words: fluoride, hypertension, systole, diastole, blood pressure
In most water resources, naturally occurred levels of fluoride can be found. In surface waters, fluoride can occur naturally by deposition of atmospheric derived particles and/or by fluoride-containing soils and rocks weathering, and in ground water resources by leaching of rocks and soils. Also, fluoride makes its way into public sources of water through diverse human activities, such as chemical manufacturing plants; manufacturing of tile, brick, glass, aluminum, pottery, and cement; producing of fluorinated fertilizers; metal casting, welding, and brazing 1. National standards for drinking water are derived from World Health Organization (WHO) guidelines 2. In the latest guideline of WHO for fluoride in drinking water, it has been mentioned that teeth mottling (i.e. dental fluorosis) were sometimes correlated with levels of fluoride in drinking water above 1.5 mg/l. Also, increasing fluoride levels in drinking water were consistently associated with lower dental caries level measured as mean number of Decayed, Missing, and Filled Teeth (DMFT) for permanent teeth, and dmft for primary teeth 1, 3-4. Therefore, 1.5 mg/l of fluoride recommended by WHO as a guideline value at which dental fluorosis should be minimal, and fluoride benefits against dental caries should be obtained 5. Some reports in recent years declared that fluoride accumulates not only in bones, but also to a lesser extent, in soft tissues, particularly in cardiovascular system6. This awareness has brought about the possible correlation of fluoride with myocardial functions, and some studies have been conducted in human and animal settings for this purpose 7-8. although different aspects and effects of fluoride and fluorosis have been examined on various organ systems, fluoride effect on cardiovascular system and blood pressure has still not been well studied 9. The objective of this study is to examine the relationship between fluoride (F) in ground water resources (GWRs) and blood pressure of Iranian population in an ecologic study.
Methods
Data of F mean in GWRs of Iran for each province in mg/l, which is the main source of drinking water supply in urban and rural areas throughout whole country, was derived from previous monitoring of F in GWRs of Iran study performed in 2008 and its results were published in 2010 10. Caries-free (Cf) index of Iranian children (for both primary dentition and permanent teeth) published in 2004, was used to validate F data. Data of Cf for 6 and 9 years old children were derived from reports of Ministry of Health (MOH) of Iran11. Hypertension prevalence (percentage of individuals with blood pressure≥ 140/90 mmHg), mean systolic blood pressure (SBP) in mmHg, and mean diastolic blood pressure (DBP) in mmHg by different provinces and sex groups were derived from provincial report of non-communicable diseases risk factors surveillance of Islamic Republic of Iran published in 2007 12.
Statistical methods
Q-Q plot and Kolmogorov-Smirnov tests were used to see if the data of fluoride concentration, mean blood pressure and hypertension prevalence were distributed normally. Natural logarithm of mean concentration of F was use to compensate the right skewness of its distribution amongst the tried transformations. The relation between ln of mean F with mean blood pressure and hypertension was evaluated using simple regression analysis separately for each gender. In all analyses, p values less than 0.05 were considered as significant.
Results
Mean concentration of F data were derived from a previous study that monitored all 30 provinces of Iran had a range of 0.23 to 1.86 (table1) mg/l. Spatial distribution of F data are shown in figure 1-A 10. Also, blood pressure data by different provinces were derived from a published governmental report. The prevalence of hypertension for males and females ranged from 10.6 to 27.2 and 11.5 to 23.3 respectively (Table1). Spatial distribution of SBP of males are shown in figure 1-B 12. Statistically significant positive correlation between ln of mean concentration of F in GWRs and Cf of 6 years old children (r=0.608, p=0.001), 9 years old children (r=0.52, p=0.005), and mean of 6 and 9 years old children (r=0.581, p=0.001) were found. As shown in fig 2 and 3, statistically significant positive correlation between ln of mean concentration of F in GWRs and hypertension prevalence of males (r= 0.48, p= 0.007, a= 21.46, b= 4.52), females (r=0.36, p=0.048, a= 19.38, b= 2.34), and overall (r=0.495, p=0.005, a= 20.42, b= 3.43) were found. Also, statistically significant positive correlation between ln of mean concentration of F in GWRs and mean SBP of males (r=0.431, p=0.018, a= 125.13, b= 2.69), and a borderline correlation with females (r=0.352, p=0.057, a= 118.82, b= 2.78) were found (fig 4). No statistically significant correlation between ln of mean concentration of F in GWRs and mean of DBP in males (r=0.151, p=0.417), and females (r=0.273, p=0.144) were found.
Discussion
In this survey, the relation of F in GWRs with blood pressure prevalence of Iranians by different provinces and sex groups was investigated. GWRs are the main source of supplying water for approximately 60 percent of urban populations, and main populations of rural communities by using wells, springs, aqueducts, and/or subterranean canals in Iran 13-14. Because of right skewness of F data, normal distribution was obtained by transforming mean of F data in each province to ln of F. Because of the fact that F level of GWRs is not necessarily equivalent to F level of drinking water of Iranian populations, and since weight of current evidence supports a positive protective link between F intake from drinking water and dental caries, Cf of Iranian children were used to validate F data. Since ln of mean concentration of F in GWRs was strongly correlated with Cf of Iranian children, we assumed that F level of GWRs can be used as a good surrogate for F level in drinking water of Iranian populations. Also, because of greater relation between ln of mean concentration of F in GWRs and hypertension prevalence in males than females, we concluded that this relation can be gender specific. We did not find many similar studies in literature. In an animal study in which Wistar rats were used, there was a significant relation between blood pressure of male rats and perinatal exposure to NaF: a substantial increase in SBP of male Wistar rats treated with 5 mg/kg of NaF concentration with respect to control and 2.5 mg/kg NaF treated animals. Hence, perinatal exposure to NaF in Wistar rats resulted in a dose-dependent, long-lasting, and sex specific functional impairment in hemodynamic control 15. In another study, aortic elasticity was studied in patients who had endemic fluorosis. The result of this study showed that aortic strain (AS) and aortic distensibility (AD) in ascending aorta of patients who had fluorosis were significantly lower compared with controls. 9. Lower AS and AD in fluorosis patients is in accordance with our findings of increasing SBP (and not DBP) with increasing exposure to fluoride. In conclusion, it can be declared that with increase of F level in GWRs, hypertension prevalence and mean SBP statistically increase, especially in males. Thus, it seems that these relations can be gender specific. Finally, the authors declare that ultimate conclusions about the association of fluoride and blood pressure and its effect on cardiovascular system needs more experimental and epidemiologic studies with controlling confounding factors, and considering different conditions.
Acknowledgments
The authors acknowledge the whole hearted cooperation of oral health bureau, center for diseases control & management, and environmental and occupational health center of ministry of health and medical education of Islamic Republic of IRAN.
Source of Funding
None.
Disclosures
None.
