A Retrospective Cohort Study On The Effects Of Air Pollution On Incident Hypertension

Background:With decades of rapid development,the lifestyle of residents has changed greatly and the environmental pollution problem has been confronted with great difficulties,which have an impact on people’s health and disease burden year by year.Previous studies on air pollution and hypertension were mostly from European and American countries whereas little evidence from other regions.The situation of air pollution is grim in China,especially in the northern cities.Our previous studies found that high levels of particulate matter pollution in four northern cities was associated with increased cardiovascular mortality（HR=1.23,95%CI:1.19-1.26）.As a major risk factor of cardiovascular disease,the prevalence of hypertension in China is also severe.Therefore,it is of great significance to explore the relationship between air pollution and hypertension for the early prevention and treatment of cardiovascular diseases.Objective:A cohort study from four cities of northern China was aimed to explore the relationship between high-level air pollutants(PM₁₀,SO_2,and NO₂)and the incidence of hypertension and the incidence of other factors on hypertension.Furthermore,stratified analysis was used to explore the modifying effects of other confounding factors on the association of air pollution and hypertension.This confounding factors included age,sex,education,economic income,smoking,drinking and the intake frequency of vegetables and fruits.The study was conducted to find out whether this factors can modify the health effects caused by atmospheric pollutants,so as to screen out the sensitive population and to provide supplementing epidemiological evidence of health effects of air pollution and early prevention of cardiovascular diseases.Methods:1.About 40,000 residents from four cities in northern China（Rizhao,Tianjin,Shenyang,and Taiyuan）were selected to establish a 12-year retrospective cohort study.All communities or streets within a radius of 1 km of the urban air quality monitoring stations are selected as the screening framework.Cluster sampling was used to select about 10,000 people from each city as the research object.The baseline information was based on the household registration data of each community in 1998.Follow-up was conducted by questionnaire survey,and the follow-up outcome was the incidence of hypertension.2.The concentration of ambient air pollutants was calculated according to the data of air quality monitoring stations in cities from 1998 to 2008.Survival time was defined as the period from the entry of the cohort to the onset of hypertension or the end of follow-up.Individual exposure concentration was the average concentration during the survival time.3.Cox proportional hazard regression model was used to analyze the relationship between air pollution and incident hypertension.And potential confounding factors were incorporated into the models to adjust the association.4.Stratified analysis was used to explore the modifying effects of some individual characteristics on the health effects of ambient pollutants.These characteristics involved age,sex,education level,smoking and drinking,frequency of intake of vegetables and fruits.The interaction items between the above factors and ambient pollutants were established to verify the statistical significance of the interaction in the models.5.Sensitivity analysis was used to explore the relationship between ambient pollutants and hypertension after excluding some subjects with a history of chronic diseases and cancer.Results:1.A total of 39 054 valid questionnaires were collected after follow-up.According to the purpose of this study,37 386 subjects without hypertension were included.The total follow-up time was 426 333.51 person year with an average of11.40 years.From 1998 to 2009,2 619 subjects had self-reported（7.0%）developed hypertension.The cumulative incidence in Rizhao was 1.7%（155）,Taiyuan was 7.0%（676）,Shenyang was 9.3%（877）and Tianjin was 10.1%（911）.2.From 1998 to 2009,the environmental pollution level[mean（SD,range）]for the study cohort were 66.71μg/m³（39.06,11.00-165.90）for SO₂,40.74μg/m³（17.07,16.80-89.47）for NO₂,143.36μg/m³（53.52,58.00-259.40）for PM₁₀.3.The adjusted HR（95%CI）for incident hypertension were 1.17（1.16-1.18）for each 10μg/m³ increase in SO₂,1.20（1.17-1.23）for each 10μg/m³ increase in NO₂,and 1.54（1.52-1.56）for each 10μg/m³ increase in PM₁₀.4.Stratified analysis showed that HR（95%CI）of three pollutants and hypertension was higher among younger people（age<60）.The effect of PM₁₀was stronger in non-alcoholic and high-income subjects.The effect of SO₂ was stronger in high-education and low-frequency consumption of vegetable subjects.The subjects with low-frequency consumption of fruits and high-income were more sensitive to the effect of NO₂.5.Age,female,BMI,family history of hypertension,alcohol consumption and severe physical labor intensity were risk factors for hypertension.High-frequency consumption of vegetable and moderate-frequency consumption of fruit are protective factors for hypertension.The influence of smoking,education level and economic income on the incidence of hypertension were not statistically significant.Conclusions:1.The air pollution in four cities in northern China is relatively serious.In general,the concentrations of three pollutants exceed the second level limit of the1996 National Environmental Air Quality Standard,especially particulate matter.2.The results of this study show that high levels of PM₁₀,SO₂,and NO₂ are significantly correlated with the incidence of hypertension.After adjusting for various factors,the effect of pollutants is still statistically significant.3.Younger people are more sensitive to the effect of air pollution.Non-drinkers and high-income people are more susceptible to PM₁₀.People with high education level and low-frequency consumption of vegetable are more sensitive to the effect of SO₂.Low-frequency consumption of fruits and high-income was more sensitive to the effect of NO₂.