Identification of Normal Blood Pressure in Different Age Group (2024)

Abstract

The concept of using single criterion of normal blood pressure with systolic blood pressure (SBP) < 140 mmHg and diastolic blood pressure (DBP) < 90 mmHg for all ages is still disputable. The aim of the study is to identify the cutoff value of normotension in different age and sex groups.

Totally, 127,922 (63,724 men and 64,198 women) were enrolled for the analysis. Finally, four fifths of them were randomly selected as the study group and the other one fifths as the validation group. Due the tight relationship with comorbidities from cardiovascular disease (CVD), metabolic syndrome (MetS) was used as a surrogate to replace the actual cardiovascular outcomes in the younger subjects.

For SBP, MetS predicted by our equation had a sensitivity of 55% and specificity of 67% in males and 65%, 83% in females, respectively. At the same time, they are 61%, 73% in males and 73%, 86% in females for DBP, respectively. These sensitivity, specificity, odds ratio, and area under the receiver operating characteristic curve from our equations are all better than those derived from the criteria of 140/90 or 130/85 mmHg in both genders.

By using the presence of MetS as the surrogate of CVD, the regression equations between SBP, DBP, and age were built in both genders. These new criteria are proved to have better sensitivity and specificity for MetS than either 140/90 or 130/85 mmHg. These simple equations should be used in clinical settings for early prevention of CVD.

INTRODUCTION

It is well-known that high blood pressure (BP) is the fundamental cause for many serious cardiovascular diseases (CVD) such as cerebral vascular disease and coronary artery disease.¹ Several reports have shown that there is a continuous, graded, and strong relationships between BP and the risk CVD.^2,3 The definition of normal BP (systolic blood pressure [SBP] < 140 mmHg and diastolic blood pressure [DBP] < 90 mmHg) was first proposed by the 3rd report of Joint National committee on Detection, Evaluation and Treatment of High Blood Pressure in 1984 (JNC III).⁴ However, some of the researchers are still skeptical about this criteria. For example, Domanski et al⁵ suggested that the cardiovascular mortality could be avoided by lowering the BP down to 120/80 mmHg in both younger and middle-aged group based on data from a 22 years follow-up cohort (Multiple Intervention Trial cohort). Furthermore, by using logistic splines analytic method, Port et al⁶ also suggested that hypertension should be defined according to age- and sex-specific threshold rather than a single value. At the same time, one of the largest meta-analysis including 61 cohorts, 958,074 subjects, and 56,000 cardiovascular deaths also indicated a different value of optimal BP which is 115/75 mmHg.⁷ The results of these important studies indicated that the definition of normal BP is still under controversial.

The clustering of hypertension, dyslipidemia, and obesity have been noted early in 2001.⁸ As they are highly correlated to future occurring of the CVD and diabetes, the World Health Organization has denoted this phenomenon as metabolic syndrome (MetS) in 1998.⁹ Later, a modified and simpler version published by the National Cholesterol Education Program in 2002.¹⁰ By far, this is the most widely accepted and used criteria. It should be stressed that the original purpose to define MetS was trying to early detect subjects with high risk for CVD and diabetes. Till now, compiling results derived either in the cross-sectional or the longitudinal studies all repeatedly validated its predictability. Noticeably, in most of these pivotal studies, actual occurrences of mortality and/or morbidities were often used as the primary endpoints. It is not difficult to postulate that these endpoints are common in the elderly. However, in the younger cohort, these cardiovascular outcomes are much less to be found. To have enough number for an observational study to become statistically significant would take a long time which is difficult for many of the researchers. Unfortunately, the aforementioned definition for normotension derived from older cohort is being applied to all age groups at present, and it is easily to understand that this is just not reasonable. Ever since the publication of the notion of MetS, there are many longitudinal studies focusing on its predictable CVD.^11–13 These studies unanimously showed positive results and were published in some of the best journals. Thus, MetS could be used as a surrogate to replace the actual cardiovascular outcomes in the younger subjects. Although it is less accurate, by using this method, we could re-evaluate the more logical cutoff points of normotension in the younger population.

Other than this, it is also important to note that both SBP and DBP change as age increases.¹⁴ In other words, age plays a very important role in the regulation of BP. Therefore, we hypothesized that the definition for normal SBP and DBP should vary rather than using the same value in all age-groups.

In this cross-sectional study, we enrolled 127,922 subjects. Four fifths of the subjects were used to build an equation from the logistic regression lines of SBP and DBP to have MetS in different gender. The levels of BP calculated from these curves could detect either CVD or diabetes more precisely and should be regarded as the definition of hypertension in its corresponding age and sex groups. Finally, these equations are further verified and compared with the present standard of normal BP in the remaining one fifths of the subjects.

MATERIALS AND METHODS

RESULTS

The demographic data of the study and validation group for males and females is displayed in Table 1. By the grouping criteria, it could be expected that there were no significant difference in demographic and major MetS components between the 2 groups. However, between subjects with and without MetS, it could be noted that all the components were significantly different which is not surprizing. As it is explained in the method, the cutoff values for proper SBP and DBP were determined by using the logistic regression and ROC curve for each 5-year age group. These results are showed in Table 2. These cutoff points for SBP and DBP in both males and females were plotted against the age and are showed in Figure 1. It could be noted that for both genders the SBP concave down a little bit between 30 and 40 years old. On the other hand, the curves are quite different for DBP. The line for male is a sigmoidal curve. Compared to it, the relationship between age and DBP is a straight line in females. From these lines, equations were built and then were used in the validation groups for predicting MetS. The positive predict value, negative predict value, sensitivity, and specificity of different BP cutoff points are shown in Table 3. For SBP, MetS predicted by our equation had a sensitivity of 55% and specificity of 67% in males and 65%, 83% in females, respectively. At the same time, they are 61%, 73% in males and 73%, 86% in females for DBP, respectively. These sensitivity and specificity are better than those derived from the criteria of 140/90 or 130/85 mmHg. Table 4 shows the ORs derived from the logistic regression of the various criteria of BP predicting MetS. As expected, the ORs estimated by our equations were better than conventional normotension criteria in both genders.

Finally, Figure 2 shows the ROC curves of the 3 different normotension criteria. The areas under ROC from our equations were unanimously the highest one in either SBP or DBP in both genders. All of them reached statistical significance.

DISCUSSION

The present criteria of normal BP was first proposed by JNC III. It was determined according to several large-scale, prospective, and observational studies by using stroke and coronary heart disease as the primary end points. However, the concept of using 1 criterion for all ages is still disputable. For instance, it is hard to be agreed that a 20-year-old subject would under the same CVD risks compared to a 65-year-old subject if they all had a BP of 130/80 mmHg. One may argue about the justifiability to use MetS as an endpoint for determining the cutoff values of BP. However, as mentioned earlier in the introduction, we have several reasons to rationalize this method. First, the traditional definition of normal BP is derived from the older subjects. Caution must be taken when exercise this definition into young adulthoods. Second, it is practically very difficult to follow a person from young to old age. Before further longitudinal study by using CVD as the endpoint in young adults could be done, our results provide a new concept to define “normal” BP. Third, Ford¹¹ had published his milestone study in Diabetes Care by observing all the major longitudinal studies focusing on the predictability of MetS. Although these studies used different endpoints (coronary heart disease, myocardial infarction, stroke and diabetes, etc.), the results unanimously support the values of MetS. Fourth, it is undoubtable that each component of MetS is independently related to future CVD and diabetes. Thus, the collectively correlations of these components should be better than the single component.

In the present study, equations for SBP and DBP were built separately in men and women. By putting the ages into these equations, the levels of normal SBP and DPB for that age will be calculated. The results of ROC curve showed that our revised criteria have unanimously higher predictive power for MetS than that of the traditional criteria in both genders. In other words, the tradition generalized criteria of hypertension for all ages are challenged.

Most evidences have shown that SBP increases with age. However, DBP increases first before 45 years old and then declines afterwards. The main underlying mechanism of this age-related changes of BP might be caused by the arterial stiffness.^14,18–21 In their longitudinal study, Safar et al¹⁹ found that the relationships between SBP, DBP, and ages are linear and curvilinear, respectively, in a healthy population. Similar to the grouping criteria used in Framingham and Safar's studies, we divided our subjects into 5-year-old subgroups. Four equations were made to define the threshold of BP for having MetS in both genders. Not surprizingly, as age increases, the cutoffs of SBP rise in both sexes. In the same time, this linear relationship was only found in the DBP of females. The curve of DBP in male is an interesting exception which is a sigmoid line and has the lowest values between 31 and 40 years old (75.5 mmHg) and the highest at 46 and 55 (80.5 mmHg). This finding might be attributed to the interference of some risk factors other than the MetS components, such as smoking or low-density lipoprotein cholesterol, which were not analyzed in the present study. Further well-designed research is needed to elucidate this issue.

Pathologically, the mechanisms of increased SBP and DBP in hypertensive patients are not the same. The elevation of SBP is partly caused by the increased cardiac output, reduced large arteries compliance and the rise of peripheral resistance.^22,23 However, in the general population, diseases resulting in increase of the cardiac output, such as anemia, hyperthyroidism aortic regurgitation, and arteriovenous fistula, etc. are relatively few. In other words, age-related arterial rigidity and resistance play the most important role in the “systolic hypertension.”¹⁸ As age increases or atherosclerosis advances, the elasticity of aorta decreases which followed by the increased SBP and reduced DBP. Interestingly, DBP is considered to be the main target of treatment for the young people while, in the elderly, SBP is the goal.^18,20 In this study, we believed that our criteria are more sensitive for detecting subjects with risks since it is age- and sex-specific.

It is well-recognized that gender differences in BP starts since adolescence.²⁴ After puberty, females generally have lower BP than males. This difference might be caused by the higher androgen secretion in males. This hypothesis could be supported by either the human or the animal studies. For example, in females with polycystic ovary syndrome, the BP increases.²⁵ On the other hand, in castration male rats which have decreased androgen, the BP parallels with the change of the hormone.²⁶ Results of observational studies in human beings also suggest the protection role of estrogen against hypertension since higher BP is noted after menopause.²⁵ However, some reports showed that there was no significant reduction of BP after replacement of estrogen in the menopause females.^27,28 The discrepancy might be explained by the possibility that the abrupt decline of estrogen in menopause women might not be the only component responsible for increase of BP.^27,28 For instance, other than the drop of the estrogen, a mild decrease of androgen secretion was also noted which could modulate BP through the rennin-angiotensin-aldosterone system and oxidative stress.²⁹ Because of these aforementioned reasons, our data highly suggest that the definition of normal BP should be gender-specific.

To our knowledge, this is the 1st study trying to define normotension criteria in subjects with different age and genders. However, there are still some limitations in our study. First, this is a cross-sectional study which is less powerful. A longitudinal study may yield more conclusive results. Second, it should be noted that only Chinese were enrolled in this study. In other words, it should be exercised with caution when being extrapolated to other ethnic groups.³⁰ Third, some important confounding factors were not available in the data bank such as exercise and smoking status and thus could not be adjusted. This would reduce the reliability of our results. However, because of the number of cohort is quite substantial, this drawback could be justified.

In conclusion, by using the presence of MetS as the surrogate of CVD and diabetes outcomes, the regression equations between SBP, DBP, and age were built, respectively, in males and females. All the regression lines are straight except for the DBP in males. From these equations, cutoff values for normotension are redefined. By using ROC curves, these new criteria are proved to have better sensitivity and specificity for MetS compared to either 140/90 or 130/85 mmHg. We believe that these simple equations should be used in clinical settings for early detection of and prevention of CVD.

Acknowledgments

The authors thank all participants in the study.

Footnotes

REFERENCES