Study results indicate that level of education is inversely associated with SBP in a diverse cohort of community-living older adults, independent of numerous risk factors for hypertension. Multivariable regression and path analysis results show that risk factors attenuated the association between educational attainment and SBP but did not nullify the significant association. This study replicates finding from similar studies involving younger participants and additionally offers new findings of importance. First, this study is the first to report the association between education and SBP in an older sample, representing a population at the highest risk for hypertension-related morbidity and mortality. Second, in cross-sectional studies involving younger adults, it is difficult to identify the temporality of the relationship between education and SBP. However, in the current study most participants were in their seventh decade, suggesting a distant effect of education on SBP, as education was likely completed decades before the SBP assessment. Thus, level of education could have influenced SBP.
A third important finding of the present study is because older individuals are at the highest risk of hypertension-related morbidity and mortality, it is possible to apply findings from studies involving older individuals at risk for hypertension-related cardiovascular disease. For example, higher SBP is associated with an elevated risk of heart disease. Published multivariable-adjusted proportional-hazards regression analyses using Framingham Heart Study participants aged 60 years and older indicate that a 10 mmHg increase in SBP is associated with a 17% increased risk of developing coronary heart disease (CHD) [26
]. Applying this information to our findings with education and SBP, MBS participants with less than or equal to a high school education would have approximately a 11% increased risk of developing CHD relative to those with higher than a college education, independent of many known risk factors. The difference between a college degree and graduate school represents approximately a 7% increase in CHD risk.
The findings of this study of older adults are consistent with published cross-sectional and longitudinal studies of younger adults. Using a nationally representative sample of 14 000 young adults (mean age 29 years), Brummett et al
] assessed the association of SES and SBP and examined the role of potential mediators. They reported that higher income and education were significantly associated with lower SBP in the age-adjusted, sex-adjusted and medication-adjusted analyses but the education association statistically lost significance after further adjustment for BMI, waist circumference and heart rate. In contrast, the present study and another [27
] reported income and education were associated with SBP or hypertension in unadjusted analyses, but only education was associated with SBP or hypertension after multivariable adjustment. Differences in findings may be partially explained by age differences of study participants and meanings of income and education in these samples. In younger populations, income can fluctuate over time and is thus susceptible to misclassification. In contrast, income in an older population, wherein persons may have accumulated wealth and are earning social security and pension, may have a different relationship with health-related behaviors than in a younger population that is actively working [27
]. Moreover, education is likely more static in an older population relative to a younger population, making it a more influential predictor of behaviors than other known risk factors associated with hypertension.
Loucks et al
] examined the association between SBP and education level among 3890 participants of the Framingham Offspring Study (mean age 37 years). Using multiple longitudinal assessments, multivariable-adjusted mixed linear models revealed that education level was inversely associated with SBP. However, this study did not adjust for income, which has been shown to be associated with education and SBP in the current study as well as other studies [6
Conen et al
] prospectively examined the association between education and blood pressure progression and incident hypertension among 27 207 female health professionals (mean age 54 years). After multivariable adjustment, lower educational level was significantly associated with increased risk of blood pressure progression and incident hypertension.
Diez Roux et al
] studied 8555 participants (mean age 53 years) longitudinally over 9 years. Proportional hazards regressions revealed that lower education level was associated with a higher likelihood of being hypertensive after adjustment for age and sex. These associations were only marginally significant when further adjusted for baseline blood pressure.
Strand and Tverdal [11
] studied the effects of educational inequalities in cardiovascular risk factors longitudinally in 48 422 Norwegian residents (age range 35–49 years). Based on sex-stratified mixed effects linear age-adjusted models, they found that higher education level was associated with lower SBP.
Among 2913 participants aged 18–30 years, Yan et al
] found that those with less than a high school education had an average 15-year mean increase in SBP of 8.2 mmHg, whereas participants with greater than a college degree education had an average 15-year mean increase in SBP of only 0.7 mmHg. Although this longitudinal difference was not adjusted for potential confounders, it was statistically significant.
A limitation of this study is that its cross-sectional design limits causal inferences. However, given the average age (78 years) of the participants, it is very likely that their level of education was completed many decades before the SBP assessment, suggesting that education was attained long before the SBP assessment. Another limitation is that we were unable to account for some factors that might influence the association between education and SBP, such as family history of hypertension, genetic profiles, diet, waist circumference, stress and occupation. An additional limitation is that persons with cognitive impairment (MMSE <18) were excluded from the study. Older adults living with dementia tend to have lower blood pressures [28
] and less education [30
], which would weaken associations found in our study. Thus, our findings may not generalize to more cognitively impaired populations. Finally, MBS participants were older, community-living and predominately white; accordingly the findings may not generalize to individuals of different races or residences.
Other possible mechanisms should be considered in future research. Family history of hypertension may partially account for the association between education and SBP. Genetic heritability of intelligence is about 50% [31
]. Parental blood pressure was reported as a strong determinant of the natural history of blood pressure in their offspring from childhood into young adulthood [32
]. Genetic profiles may also influence the association between education and SBP [33
]. Diet is known to be associated with hypertension and education. A diet rich in fruits, vegetables and low-fat dairy products, and reduced saturated and total fat intake, was associated with reduced blood pressure [34
]. Sodium intake was reported to decrease as educational level increased [35
]. Intake of energy from fat and dietary cholesterol has been shown to decrease [36
], and intake of fruits and vegetables increase by increasing level of education [36
]. Lower educational attainment has been associated with stressful jobs involving high demands and low job control, which have been associated with hypertension [38
The findings of this study strongly suggest that educational attainment is inversely associated with SBP in a community-living cohort of older individuals, independent of many risk factors for hypertension. The results are consistent with previous studies of younger individuals and suggest that a considerable proportion of CHD may be attributable to the influence of low education on hyper-tension. Given the relatively low amount of total variance in SBP that is explained by education, other factors not examined in this study are likely involved in this association. Future studies should examine genetic, nutritional and other factors that might further help to explain the complex association between educational attainment and SBP in elderly people.