Fluoride In The Drinking Water

Transcription

1 Fluoride In The Drinking Water Linuz Aggeborn 1,2 Mattias Öhman 1,3 1 Department of Economics, Uppsala University 2 Uppsala Center for Fiscal Studies (UCFS), Uppsala University 3 U-CARE, Uppsala University August 23, 2016 EEA-ESEM Geneva 2016 Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

2 Fluoride is good for teeth, therefore many countries in the world fluoridate the drinking water as a public health measure. However, there is an intense debate whether fluoride has negative effects on cognitive development. A meta-study by Choi et al. (2012) found that higher fluoride levels decreased IQ with half of a standard deviation. These fluoride levels are found in many parts of the world (naturally or artificially). Highly policy relevant question. We study the effects of fluoride exposure through the drinking water age 0-16 on cognitive ability, dental health and later labor market outcomes. We use large register datasets with a more credible identification strategy than earlier epidemiological papers. Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

3 Fluoride is a natural compound and is lethal in higher dosages. Known cases of fluoride poisoning lower than the lethal level. Animal trials conclude that rats exposed to high levels of fluoridated water have impaired memory and symptoms of behavioral changes (Mullenix et al., 1995, Chioca et al., 2008). No difference between natural and artificial fluoride. Natural variation of fluoride mainly due to different types of bedrock under the water sources. There are calls for a global research initiative on neurotoxins, including fluoride (Grandjean and Landrigan, 2014). Our paper is connected to the economics literature on human capital accumulation, e.g. Case et al. (2005), Cunha and Heckman (2007), Currie (2009), Cunha et al. (2010). Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

4 Identification Mapping of fluoride data Threats to identification We exploit fluoride variation between small geographical areas within municipalities. Variation mainly stems from the use of several water sources placed on different kinds of bedrock. Fluoride level is likely independent of the labor market structure between these small areas. Additional variation due to moving patterns. We confirm in various balance tests that the fluoride level is independent of the choice to move. Because fluoride is tasteless, colorless and without any odor, the general public is unaware of the fluoride level in the water. The within-municipality variation means that we can control for characteristics on the municipal level by using fixed effects. Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

5 Identification Mapping of fluoride data Threats to identification (a) Before mapping (b) After mapping Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

6 Identification Mapping of fluoride data Threats to identification We have run several balance tests to conclude that fluoride is independent of background characteristics. We find no evidence that municipalities reroute high/low fluoride water to certain socioeconomic neighborhoods. The effects of fluoride could be influenced by nature and nurture channels through parents fluoride exposure. We address this by 1 Running all specifications for adoptees. 2 Including intergenerational covariates. Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

7 Swedish individual register data for outcomes and covariates. Dental measures for each cohort and SAMS. Main outcome variables: Cognitive ability, non-cognitive ability, points on national math test, annual income and employment status. We have various dental health outcomes, such as the number of visits to a dentist and dental repair. We expect to find an effect of fluoride! Dental outcomes used to assess our mapping strategy. Birth Age 16 Age 18 Year 2008, Year Fluoride treatment Enlistment (only males) National test Dental outcomes Income, employment Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

8 Dental outcomes Cognitive ability Annual income Table: Dental outcomes F. Visit Repair RiskEvaluation DiseasePrevention DiseaseTreatment RootCanal (0.299) (0.110) (0.302) (0.431) (0.139) (0.0173) (0.293) (0.0684) (0.320) (0.224) (0.106) (0.0198) Notes: Standard errors clustered at the municipal level. *** p < 0.01, ** p < 0.05, * p < 0.1. Individuals aged 20. The number of observations for the year 2013 is 7,622. The number of observations for the year 2008 is 7,606. Fluoride expressed in 0.1 mg/l. Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

9 Dental outcomes Cognitive ability Annual income Table: Cognitive ability (1) (2) (3) (4) (5) (6) (7) Fluoride (0.1 mg/l) (0.0081) (0.0051) (0.0051) (0.0052) (0.0039)* (0.0050) (0.0081)*** {0.0085} {0.0045} {0.0045} {0.0051} {0.0041}* {0.0050} {0.0092}** Mean Birth cohort FE No No Yes Yes Yes Yes Yes Birth municipal FE No Yes Yes Yes Yes Yes Yes Large set covariates No No No No Yes Yes Yes Sample All All All Col 5 All SAMS stayers SAMS movers R Observations 82,010 82,010 82,010 51,322 51,322 21,348 18,848 Notes: Standard errors in parenthesis are clustered at the municipal of birth. Standard errors in curley brackets are Conley standard errors with a cut-off of 10 km, centered on each SAMS. *** p < 0.01, ** p < 0.05, * p < 0.1. Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

10 Dental outcomes Cognitive ability Annual income Table: Annual log income in SEK (1) (2) (3) (4) (5) (6) (7) (8) Fluoride (0.1 mg/l) (0.0032)** (0.0015)*** (0.0014)*** (0.0013)*** (0.0012)*** (0.0010)*** (0.0016) (0.0031) [0.0018]*** [0.0017]*** [0.0016]*** [0.0009]*** [0.0010]*** [0.0010]*** [0.0016] [0.0029] {0.0031}** {0.0010}*** {0.0010}*** {0.0010}*** {0.0010}*** {0.0009}*** {0.0014}* {0.0024} Mean Birth cohort FE No No Yes Yes Yes Yes Yes Yes Birth municipal FE No Yes Yes Yes Yes Yes Yes Yes Municipal FE, year 2013 No No No Yes Yes Yes Yes Yes Small set covariates No No No Yes Yes Yes Yes Yes Large set covariates No No No No No Yes Yes Yes Sample All All All All Col 6 All SAMS stayers SAMS movers R Observations 628, , , , , , , ,980 Notes: Individuals with a yearly income below 1,000 SEK are excluded. Standard errors in parenthesis are clustered at the municipal of birth. Standard errors in brackets are clustered at the local labor market area defined by Statistics Sweden (SCB). Standard errors in curley brackets are Conley standard errors with a cut-off of 10 km, centered on each SAMS. *** p < 0.01, ** p < 0.05, * p < 0.1. Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

11 In contrast to recent epidemiological papers, we find no effects of fluoride on cognitive ability. No evidence that fluoride below the WHO threshold level of 1.5 mg/l has adverse effects. In comparison to earlier studies, our estimates are much more precise and our sample much larger with almost the full population for the included cohorts. We find that higher fluoride levels are positive for the dental health. We also find that higher fluoride levels increase the annual income, probably due to better dental health. Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 11

12 References Case, A., A. Fertig, and C. Paxson (2005). The lasting impact of childhood health and circumstance. Journal of Health Economics 24(2), Chioca, L. R., I. M. Raupp, C. Da Cunha, E. M. Losso, and R. Andreatini (2008). Subchronic fluoride intake induces impairment in habituation and active avoidance tasks in rats. European Journal of Pharmacology 579(1 3), Choi, A. L., G. Sun, Y. Zhang, and P. Grandjean (2012). Developmental fluoride neurotoxicity: A systematic review and meta-analysis. Environmental Health Perspectives 120(10), Cunha, F. and J. Heckman (2007). The technology of skill formation. The American Economic Review: Papers & Proceedings 97(2), Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 2

13 References Cunha, F., J. J. Heckman, and S. M. Schennach (2010). Estimating the technology of cognitive and noncognitive skill formation. Econometrica 78(3), Currie, J. (2009). Healthy, wealthy, and wise: Socioeconomic status, poor health in childhood, and human capital development. Journal of Economic Literature 47(1), Grandjean, P. and P. J. Landrigan (2014). Neurobehavioural effects of developmental toxicity. The Lancet Neurology 13(3), Mullenix, P. J., P. K. Denbesten, A. Schunior, and W. J. Kernan (1995). Neurotoxicity of sodium fluoride in rats. Neurotoxicology and Teratology 17(2), Linuz Aggeborn, Mattias Öhman Fluoride In The Drinking Water August 23, / 2