People who've had no more than a high school education had consistently higher systolic blood pressure over a 30-year period compared with those who did at least some graduate work after college, according to a major longitudinal study.
The study of almost 4,000 individuals found that, after adjusting for age, women with 12 or fewer years of education had systolic pressures that were higher by an average of 3.26 mm Hg (95% CI 1.46 to 5.05) compared with women who had at least 17 years of education, Eric Loucks, PhD, of Brown University's Department of Community Health, and colleagues, reported.
The difference was smaller -- but still significant -- among men (2.26 mm Hg, 95% CI 0.87 to 3.66), Loucks and co-authors wrote online in BMC Public Health.
Educational attainment has been inversely associated with rates of cardiovascular disease in developed countries, and blood pressure may at least partly explain the relationship, since hypertension has been associated with education and other socioeconomic variables.
To further explore the issue, Loucks and his colleagues turned to the Framingham Offspring Study, which began in 1971, and provided seven longitudinal health assessments for the participants from 1971 to 2001.
The analysis included 3,890 participants (52% of whom where female) with a mean age at baseline of 36.7.
For current the analyses, educational attainment was divided into three groups: ≤12 years (reflecting high school or less), 13-16 years (indicative of some post-secondary education, including technical school and college degree) and ≥17 years education (approximating those with more than an undergraduate college degree), the authors explained.
Overall assessments averaged for the 30-year study period found that mean systolic blood pressure was significantly higher for both men and women who had ≤12 years of education -- compared with those who had ≥17 years of education, after adjustment for age.
Further adjustment for antihypertensive medication use, smoking, body mass index (BMI), and alcohol consumption reduced the difference to 2.86 mm Hg (95% CI 1.13 to 4.59) for women -- and eliminated a significant difference among men (1.25 mm Hg, 95% CI -0.16 to 2.66).
Loucks and his colleagues then repeated the analyses with adjustment for baseline systolic blood pressure to evaluate whether contributions remained from educational variables and other factors on post-baseline blood pressure.
In the fully adjusted model, women with the least education still had higher systolic blood pressures than those with the most education (2.53 mm Hg, 95% CI 0.93 to 4.14).
"This suggests that low education may have a long-term impact on changes over time in blood pressure in females," Loucks and co-authors wrote.
However, there were no significant differences in blood pressure among men based on education level.
The sex-by-education interaction was marginally significant (P=0.046), suggesting that any effects that education may have on blood pressure were stronger among women.
Similar analyses of education and diastolic blood pressure generally resulted in weaker associations -- and provided nonsignificant findings for both sexes after adjusting for age, baseline blood pressure, antihypertensive medication use, smoking, BMI, and alcohol.
According to Loucks and colleagues, the most likely mechanisms to explain an association between education and blood pressure related to the conventional risk factors for hypertension, including smoking, obesity, antihypertensive use, and alcohol consumption.
Adjustment for those factors partly attenuated the associations in women and eliminated them in men, "suggesting that they may be at least partial explanatory pathways for the observed association between educational attainment and longitudinal trajectories of blood pressure."
But other factors could be involved, including several that were not accounted for in the current analysis, like socioeconomic circumstances, parental blood pressure, intelligence, and early-life obesity.
"Consequently, residual confounding remains a possibility," the researchers explained.
Unhealthier eating habits and an increased likelihood of having a high-stress job -- both of which have been associated with lower educational attainment -- could also provide part of the explanation, they noted.
The authors acknowledged some limitations to their study, including the largely white sample, expected residual confounding due to the imperfect measurement of BMI, as well as self-reported alcohol consumption, smoking, and antihypertensive use.