Compared to four other risk factors, high systolic blood pressure had the largest impact on mortality in Iran, causing an estimated 80,000 annual deaths in 2005, according to researchers at the Tehran University of Medical Sciences, Harvard School of Public Health, the Iranian Ministry of Health and Medical Education, IHME, and Imperial College London. This research, published in the study “National and subnational mortality effects of metabolic risk factors and smoking in Iran: a comparative risk assessment,” demonstrates the need for interventions to manage blood pressure, as well as other risk factors, in the Iranian population.
Iran has experienced major demographic changes over the past few decades, with the number of adults older than 64 years of age increasing from 3.7% of the population in 1976 to 5.5% of the population in 2006. Chronic diseases, especially cardiovascular disease, have become a more prominent cause of death, as well. It is important to know how cardiovascular risk factors influence mortality for planning and allocating resources, but previous studies in Iran were based on data that were not nationally representative and did not take into account the fact that risk factors are associated with cardiovascular disease below clinical thresholds.
The authors used a health examination survey with nationally and provincially representative data on risk factors and new methods that help adjust for incompleteness of mortality registration in Iran to estimate the mortality effects of metabolic and lifestyle risk factors (smoking and high systolic blood pressure, fasting plasma glucose, total cholesterol, and body mass index) to understand how these risk factors affect mortality in Iran as a whole, as well as by province.
There were an estimated 352,000 deaths in Iran in 2005. Of these, 53% of deaths in people over age 30 were due to cardiovascular disease. The researchers found that high systolic blood pressure was responsible for 41,000 deaths in men and 39,000 deaths in women in Iran. If systolic blood pressure was reduced to optimal levels, life expectancy at birth would increase by 3.2 years in men and 4.1 years in women. High systolic blood pressure was also responsible for the largest number of deaths in every region studied, with regional age-standardized attributable mortality ranging from 257 to 333 deaths per 100,000 adults.
High fasting plasma glucose, body mass index, and total cholesterol were responsible for about one-third to one-half of the number of deaths attributable to systolic blood pressure in men and women. Smoking had the smallest mortality effect and was responsible for 9,000 deaths in men and 2,000 deaths in women.
The authors conducted a population-level comparative risk assessment for five modifiable risk factors to estimate the number of deaths that would have been prevented if past and current exposure to these risk factors were reduced to a hypothetical alternative and optimal distribution, as well as the life expectancy lost due to these risk factors. Means and standard deviations for the metabolic risk factors were estimated with data from the Non-Communicable Disease Surveillance Survey, which is representative at the national and provincial level and was conducted between December 2004 and February 2005 in all provinces.
Since death registration data are often incomplete or inaccurately coded, the authors used death distribution methods to correct for incompleteness and logistic regression methods to estimate the true underlying medical causes of deaths.
These results show that management of blood pressure through diet, lifestyle, and pharmacological interventions should be a priority in Iran and that interventions for other metabolic risk factors and smoking can also improve population health. Iran does have a hypertension control program, but it only focuses on high-risk patients. A greater emphasis on reducing blood pressure at the population level could be implemented through better treatment in primary care and public health initiatives to reduce salt in food.
The authors note that future studies should include information on dietary factors, physical activity, alcohol and drug use, and other metabolic risk factors, such as lipoproteins. They also stress the need for periodic risk factor surveillance studies to measure trends, especially among the elderly, as the demographic and epidemiologic transitions in middle-income countries like Iran will lead to an aging population. Decision-makers can use such studies to evaluate how well existing public health policies are working in their populations.