Background and purpose: This study aimed at estimating the relationship between air pollution and mortality rate due to cardiovascular diseases (CVD) in Mashhad, Iran 2011, using negative binomial regression.

Materials and methods: The dataset of mortality rates due to CVD and different types of these diseases in Mashhad were coded according to ICD 10. The dependent variable was the logaritm of the daily cardiovascular mortality. Independent variables and air pollutants were also determined. The effect of different factors and the estimation of the incidence rate ratio was done with one day lag time. Data analysis was performed in Stata software.

Results: Negative binomial regression analysis showed a significant association between the increase in air pollutants and the cardiovascular mortality. By increase in air pollutant variables including CO, SO₂ , NO_X, NO₂, and  NO  the incidence rate ratio had increased by 1.23 CI:(1.10,1.37), 1.03 CI:(1.01,1.05), 1.001 CI:(1.001,1.003), 1.01 CI:( 1.006,1.014), and 1.002 CI:(1.001,1.003), respectively. No significant relationship was found between the PM₁₀ and PM_2.5 and the incidence rate of cardiovascular death. Increase in O₃ had an inverse impact on the increase of mortality incidence rate 0.98 CI:(0.97,0.99).

Conclusion: Among the air pollutants, CO had the highest effect on CVD death and O₃ had a significant inverse impact on CVD mortality rate.