Switching from JNC8 to the 2017 ACC/AHA created a sharp rise in the prevalence and a drastic decline in awareness, treatment, and control of HTN. Based on the 2017 ACC/AHA, half of the study samples fell into the hypertensive category. Two-thirds of adults in the hypertensive category were unaware, indicating that they were undiagnosed. About one-third of those with awareness remained untreated, and among those treated, less than 20% were under control.
The increase in prevalence upon using the 2017 ACC/AHA guideline in Iran is consistent with a similar increase in prevalence upon using this guideline in other countries e.g. Nepal , China , and the United States [24, 25]. By adopting the new guideline, the largest increase in prevalence was observed among young and middle-aged individuals, which has also been reported in China .
The prevalence and awareness of hypertension in Iran (compared based on the cut-off of 140/90 mmHg) resemble findings reported in other middle-income countries [26, 27]. Despite a higher treatment rate in Iran, the control rate stood at 39.1%, which is yet noticeably lower than Turkey, with 53.9% in 2012, and Lebanon, with 54% in 2014 .
Increases in age significantly increased prevalence, awareness, and treatment but decreased the control rate. The likelihood of an increase in prevalence grew by a higher BMI (overweight and obese), higher triglycerides, dyslipidaemia, diabetes, and previous CVD history. Studies also reported a higher prevalence among the overweight, obese [29, 30], diabetics, and those with a history of CVD . Higher awareness and treatment rates were also observed among those with comorbidities of diabetes and CVD . This indicates a higher likelihood of diagnosis and treatment in individuals living with such comorbidities.
Based on the 2017 ACC/AHA, a larger ratio of comorbid patients fell into the hypertensive category (24%, 15%, 17%, and 11% more individuals with dyslipidaemia, high triglycerides, diabetes, and CVD events, respectively). Under this guideline, many high-risk adults might be covered by pharmacologic therapies and be protected against the progression of CVD and diabetic renal diseases [5, 32].
Based on the 2017 ACC/AHA, the proportion of participants with BP>120/80 mmHg who were eligible for nonpharmacologic therapy was high. 97.9% of participants with BP>120/80 mmHg need to lower their salt intake to <5 grams/day as recommended by the WHO ; 89.6% need to consume sufficient fruits and vegetables, and 69.4% need to lose extra weight.
Though the Tanaka formula provided statistically better estimates for sodium intake in Iran , all three common formulas used to estimate sodium intake (Kawasaki, Tanaka, and INTERSALT) were systematically biased with overestimation at lower levels and underestimation at higher levels of sodium intake . In the light of this evidence, we noted that the level of salt intake in Iran was much higher than the 5 grams/day cut-off recommended by WHO, therefore even in the presence of underestimation of sodium intake calculation, sodium intake levels exceeded the recommended salt intake level. Thus, the percentage of those eligible for reducing salt intake remained quite large.
Lifestyle factors, LDL cholesterol, physical activity, and BMI had large effect sizes on lowering BP. Based on these findings, non-pharmacologic therapy in hypertensive patients may be considered to modify these lifestyle factors. The modification of these lifestyle factors could be a recommended therapy for low risk adults (ASCVD <10%) who fall into the hypertensive category under the new guideline.
We contribute to a better understanding of the burden of hypertension based on two distinctive guidelines. Considering the more aggressive cut-off point of 130/90 mmHg resulted in a greater prevalence and lower effective coverage of hypertension. The largest increase in prevalence was observed in adults aged 25-34 years. Given the large population of this age group (16.8 million) in Iran, the number of adults who fall into the hypertensive category remarkably increase from 1.2 million to 5.2 million using the 2017 ACC/AHA. Despite the lowest awareness and treatment rates in this young group, their control rate was highest among all age groups. This implies that targeting younger groups brings about greater benefits for hypertension UHC programs and for the society through maintaining health among the working as well as the reproductive population of the country . Given this potential benefit for Iran, the use of the 2017 ACC/AHA might also benefit other middle-income countries with similar population profiles .
Though adopting 2017 ACC/AHA led to a higher prevalence, yet not all adults falling into the hypertensive category were eligible for antihypertensive medications . Based on the 2017 ACC/AHA, 37.2% of Iranian adults aged >25 years (17.2 million adults) were eligible for pharmacologic therapy and based on JNC8 28.6% (13.4 million adults) of them were . With a minimum unit-cost of treatment around $38 per person , pharmacologic therapy would annually cost $653 million and $510 million, respectively, under the 2017 ACC/AHA and JNC8 for all Iranian adults aged >25 years. Thus, the treatment costs incurred for pharmacotherapy by the health system under the 2017 ACC/AHA guideline was only marginally higher than the treatment costs under the JNC8.
We found that hypertension was very poorly controlled in Iran. Control is by nature a co-creational outcome. Both patient behaviour and an effective structure and process of care play roles in improving this outcome. Based on our findings, patient adherence to a healthy lifestyle and complementary insurance may improve the control rate [29, 30, 38]. We, however, call future research to examine other dimensions of effective structures and processes e.g. evidence-based care plan [39-41] and continuity of care [42, 43] to improve hypertension control.
This research had several limitations, including the challenge of causal inferences from cross-sectional data and potential misclassifications of covariates. We claim no causal relationships as making causal inferences from cross-sectional surveys is challenging. However, some of our criteria do help infer causal relationships; we relied on a compelling theoretical causal model with regards to examining the determining factors for the prevalence, awareness, treatment, and control of hypertension. This was followed by the associations observed between the focal variables as well as holding that the examined covariates and the causes logically precede these four outcomes .
We are also aware that there are potential misclassifications of covariates, particularly salt intake and smoking. We classified the participants based on 10 grams/day cut-off for salt intake rather than the 5 grams/day recommended cut-off point. We did so as a rather small number of our participants had salt intakes of less than 5 grams/day.
With regards to our classification of smoking status, we classified never-smokers with former-smokers in the same group, which may affect the magnitude of effects this group has on the outcomes. The health outcomes of a former-smoker might still be influenced by his/her previous smoking history, which may offset the positive effects of the never-smoker on the health outcomes of interest . Furthermore, the effect of smoking status might be incompletely represented by our data choices. We focused on cigarette only and other tobacco products were excluded from our analysis.
The external validity of our findings can be reasonably maintained by the multistage random proportional to size sampling employed. Participants were from all provinces (except one province) and from both urban and rural areas. Given this, the validity of inferences about the identified relationships might be, though not assuredly, maintained over variations in persons or times .