The Incidence of Coronary Heart Disease and the Population Attributable Fraction of Its Risk Factors in Tehran: A 10-Year Population-Based Cohort Study

<div><p>Background</p><p>Data on incidence of coronary heart disease (CHD) is scarce in the Middle East and little is known about the contribution of known risk factors in this area.</p><p>Methods</p><p>The incidence of CHD and the effect of modifiable risk factors were explored in 2889 men and 3803 women aged 30–74 years in the population based cohort of the Tehran Lipid and Glucose Study, during 1999–2010. Average population attributable fraction (aPAF) was calculated for any risk factor using direct method based on regression model.</p><p>Results</p><p>The crude incidence rate in men was about twice that in women (11.9 vs. 6.5 per 1000 person-years). The aPAF of hypertension, diabetes, high total cholesterol and low-HDL cholesterol was 9.4%, 6.7%, 7.3% and 6.1% in men and 17%, 16.6%, 12% and 4.6% in women respectively. This index was 7.0% for smoking in men. High risk age contributed to 42% and 22% of risk in men and women respectively.</p><p>Conclusions</p><p>The incidence in this population of Iran was comparable to those in the US in the seventies. Well known modifiable risk factors explained about 40% and 50% of CHD burden in men and women respectively. Aging, as a reflection of unmeasured or unknown risk factors, bears the most burden of CHD, especially in men; indicating more age-related health care is required.</p></div

Baseline characteristics of the study population regarding coronary heart disease risk factors.

<p>Data are shown as mean (SD) or frequency (%).</p>a<p> For difference between men and women based on t-test for continuous and chi-square test for binary variables.</p>b<p> In participants without any diagnosed diabetes.</p>c<p> Definition of risk factors is according to the Adult Treatment Panel III. All definitions are similar in men and women except high risk age; it is ages 45 or higher in men and ages 55 or higher in women.</p><p>Baseline characteristics of the study population regarding coronary heart disease risk factors.</p

Hazard ratio, survival time ratio, odds ratio and population attributable fraction (PAF) for coronary heart disease risk factors.

a<p> For study population of 2889 men and 3803 women with at least one year of follow-up.</p>b<p> Time ratio <1.0 indicates acceleration of time to the cardiac event or shortening of event free survival time.</p>c<p> For study population of 2645 men and 3400 women with a complete follow-up. Hosmer-Lemeshow chi-square of 11.0 in men and 6.7 in women indicated appropriate logistic models.</p>d<p> A multivariable adjusted attributable fraction which is directly calculated from individuals’ data using logistic regression and considers an average of all possible sequences for removal of risk factors in the community.</p><p>Hazard ratio, survival time ratio, odds ratio and population attributable fraction (PAF) for coronary heart disease risk factors.</p

Flow chart of study population.

<p>Flow chart of study population.</p

Incidence density (95% CI)^a for coronary heart disease regarding risk factors at baseline.

a<p> Incidence density per 1000 person-years among participants with at least one year of follow-up (2889 men and 3803 women).</p>b<p> Definition of risk factors is according to the Adult Treatment Panel III.</p>c<p> Based on Log Rank test for equality of event free survival between groups.</p><p>Incidence density (95% CI)^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0105804#nt105" target="_blank">a</a>} for coronary heart disease regarding risk factors at baseline.</p

Mortality rate due to RTIs in Iran.

<p>MR: Mortality rate.</p>*<p>Including data until March 2011.</p

Distribution of RTIs leading to death in Iran.

<p>RTIs: Road Traffic Injuries.</p>*<p>Including data until March 2011.</p

Log negative log Kaplan–Meier survival against the log of time (in days).

<p>Straight lines suggest a reasonable assumption for Weibull model in both genders and parallel lines for men and women indicates reasonable proportional hazard assumption.</p

Trends of death rate per 100,000 populations in Iran by gender.

<p>Trends of death rate per 100,000 populations in Iran by gender.</p

Summary of time series analysis models.

*<p>AKAIKE Information Criterion.</p>**<p>SCHWARTZ Bayesian Criterion.</p><p>SE: Standard Error.</p