A study of children and adolescents in Yazd, Iran, has found no clear relationship between fluoride exposure from drinking water or urinary fluoride levels and a range of cardiovascular risk factors. The result may appear reassuring amid recurring public debates about fluoride and health, but the research also highlights a less visible problem in environmental epidemiology: the way scientists correct urine measurements for dilution can substantially influence the conclusions. In the cross-sectional investigation, researchers examined 161 young people aged 6 to 18 years and compared fluoride concentrations in urine and drinking water with blood pressure, cholesterol, triglycerides, fasting blood sugar, calcium and magnesium. When urinary dilution was handled by including creatinine as a separate statistical variable, the researchers found no significant association with the cardiovascular measures. A sensitivity analysis using the more conventional creatinine-standardized urine values, however, produced inverse associations with diastolic blood pressure, total cholesterol and high-density lipoprotein, or HDL. The authors caution that these latter findings should not be interpreted as evidence that fluoride protects against cardiovascular disease. Instead, they suggest that the apparent relationships may be sensitive to the mathematical method used to account for how concentrated or dilute each urine sample was.
The research addresses an important question because cardiovascular disease rarely begins as a diagnosable illness in childhood, yet many of the biological and behavioral conditions that contribute to it are established during the early years of life. Elevated blood pressure, unfavorable blood lipid profiles, impaired glucose regulation, low physical activity and dietary patterns can persist into adulthood, gradually increasing the likelihood of atherosclerosis and other noncommunicable diseases. Fluoride is best known for its role in dental health, where controlled exposure can strengthen tooth enamel and reduce the risk of cavities. At higher levels, however, fluoride can affect bone and dental tissues, and researchers continue to study whether long-term exposure has effects beyond the skeleton and teeth. Yazd, an arid city in central Iran, provides a useful setting for examining exposure because drinking water is a major potential source of fluoride and local environmental conditions can influence water chemistry. The new study was designed not to diagnose cardiovascular disease, but to investigate whether differences in fluoride exposure were statistically linked to measurable risk markers in young residents.
To estimate exposure, the investigators collected drinking-water samples from 56 points across the city’s water-distribution network. Fluoride was measured using the SPADNS method, a colorimetric technique commonly used in water analysis. In this procedure, fluoride reacts with a zirconium-dye complex, altering the color of the solution; the change can be quantified to estimate fluoride concentration. The average fluoride level in the sampled drinking water was 0.53 milligrams per liter, with a standard deviation of 0.15 milligrams per liter. The researchers also gathered information through questionnaires, including demographic characteristics, physical activity and factors that might influence fluoride exposure. Urinary fluoride was measured with an ion-selective electrode, which detects the activity of fluoride ions through a specialized membrane and converts that electrical signal into a concentration. Urine provides a short-term biological measure of fluoride intake because the kidneys excrete much of the absorbed fluoride, although the amount measured can vary depending on hydration, kidney handling and the timing of exposure.
The participants had a mean age of 11.95 years, with a standard deviation of 3.74 years, and 77.6 percent were girls. Their average urinary fluoride concentration was 0.49 milligrams per liter, with a standard deviation of 0.29 milligrams per liter. Alongside the exposure measurements, the study team recorded blood pressure and analyzed blood samples for low-density lipoprotein cholesterol, HDL cholesterol, triglycerides, total cholesterol, fasting blood sugar, calcium and magnesium. These measurements represent several pathways associated with future cardiovascular health. LDL can contribute to the accumulation of cholesterol-rich plaques in artery walls, while HDL is involved in transporting cholesterol away from tissues, although the relationship between HDL levels and health is more complex than the simplified idea that higher is always better. Triglycerides reflect circulating fats influenced by diet and metabolism, and fasting blood sugar provides information about glucose regulation. Blood pressure, especially when elevated over time, places mechanical stress on arteries and the heart. None of these individual measurements, however, can establish that a child will develop cardiovascular disease.
The primary statistical analysis found no significant association between urinary fluoride and the cardiovascular risk factors after urinary creatinine was included as a separate covariate. Creatinine is a waste product generated by muscle metabolism and excreted relatively steadily by the kidneys. Because urine can be diluted by drinking fluids or concentrated by dehydration, researchers often divide the concentration of a chemical in urine by the creatinine concentration, reporting the result in milligrams per gram of creatinine. This adjustment is intended to make samples more comparable. But creatinine production varies with age, sex, body size, muscle mass and other physiological factors, all of which can be particularly important in children and adolescents undergoing rapid growth. Treating creatinine as a separate covariate rather than using a simple ratio can sometimes reduce distortion caused by that variability. In this study, the distinction mattered: the primary model did not identify a meaningful link between fluoride and blood pressure, blood lipids, glucose or mineral concentrations.
The researchers did observe that fish consumption was associated with urinary fluoride concentrations. That finding is biologically plausible because fish and other seafood can contain fluoride, particularly in edible bones or tissues, and dietary patterns can influence urinary measurements independently of drinking water. The result also illustrates why exposure assessment is difficult. A single urine sample may reflect recent meals, water intake, personal habits and the time elapsed since exposure, rather than a person’s long-term average fluoride burden. Drinking-water measurements provide information about an environmental source but do not reveal how much water each participant consumed or how much fluoride came from food, toothpaste or other products. Questionnaires can help identify these pathways, but they are subject to recall errors and cannot fully capture day-to-day variation. Together, these limitations mean that a weak or inconsistent association in a small study may reflect measurement uncertainty rather than a definite absence of any biological effect.
In a sensitivity analysis, the investigators used conventional creatinine-standardized urinary fluoride values instead of the primary covariate-adjusted approach. Under that method, higher standardized urinary fluoride was inversely associated with diastolic blood pressure, total cholesterol and HDL cholesterol. An inverse association means that higher measured fluoride corresponded statistically to lower values of the outcome, but it does not demonstrate that fluoride caused those lower values. The simultaneous association with HDL also complicates any simplistic interpretation, because HDL is traditionally considered protective in some cardiovascular contexts. Statistical patterns can emerge from chance, unmeasured factors, selection effects or the mathematical behavior of ratios. Creatinine standardization can create bias when the denominator is related to the outcome or differs systematically between groups. The authors therefore interpret the sensitivity-analysis results as evidence that the findings are dependent on the urine-dilution adjustment method, not as proof of a cardiovascular benefit or harm caused by fluoride.
The study’s design places firm limits on what can be concluded. Because it was cross-sectional, exposure and health measurements were collected at roughly the same point in time. Such a design can identify correlations but cannot establish temporal order, a necessary condition for determining causation. The sample included only 161 participants, and the predominance of girls may limit how broadly the results apply to the wider youth population. Children’s bodies and behaviors also change rapidly with age, making it important to account carefully for growth, puberty, diet, socioeconomic conditions, body composition, physical activity and family health history. The researchers used independent t-tests, chi-square tests and univariate and multivariate linear regression models to examine the data, but statistical adjustment cannot remove the effects of variables that were not measured or measured inaccurately. Nor can one city’s water chemistry represent fluoride exposure in other regions. The findings are consequently best viewed as a local snapshot and a methodological warning rather than a final answer about fluoride and cardiovascular health.
The investigators conclude that they found no association between fluoride in drinking water or urine and the cardiovascular risk factors assessed in Yazd’s children and adolescents. Their cautious interpretation is consistent with the primary analysis, while acknowledging that conventional creatinine correction generated different signals. Resolving that uncertainty will require larger, longitudinal studies that follow participants over time and repeatedly measure both exposure and health outcomes. Future research could combine multiple urine samples with detailed dietary records, precise measurements of water intake, toothpaste exposure and other fluoride sources, as well as biomarkers that better represent long-term exposure. It should also examine kidney function, growth stage, body composition and the statistical properties of different urine-dilution methods before drawing conclusions. Randomized exposure experiments would be neither practical nor ethical for this question, so well-designed observational research will remain essential. For now, the study does not support claims that ordinary fluoride exposure in Yazd is linked to altered cardiovascular risk in young people, but it shows why apparently dramatic associations can depend on how a sample is analyzed.
The work, published in the open-access journal Environmental Health, was conducted by researchers affiliated with Shahid Sadoughi University of Medical Sciences in Yazd and Kerman University of Medical Sciences, with support from Iran’s National Institute for Medical Research Development and Shahid Sadoughi University. The study received ethics approval, and written consent was obtained from parents or legal guardians, with verbal assent from the participating children and adolescents. Its broader message extends beyond fluoride: environmental health findings often hinge on how exposure is measured, how biological variability is modeled and whether a result survives alternative analyses. In an era when isolated statistical associations can spread rapidly online, the Yazd study offers a useful counterpoint to sensational claims. The headline result is not that fluoride has been shown to change children’s cardiovascular systems, but that this particular investigation detected no robust relationship—and that a method used to normalize urine samples can alter the apparent pattern. That distinction is central to interpreting the evidence responsibly.
