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The problem with those studies, according to the authors of this one, is that results are based on a single assessment of anxiety and depression at the start of the study.
Conversely, this study includes three sets of measurements of anxiety and depression and blood pressure taken at the start of the study, after 11 years, and again after 22 years. Study participants included 17,410 men and women who took part in the Norwegian Nord-Trondelag Health Study. The researchers found that high levels of combined anxiety and depression symptoms at the start of the study were associated with lower average systolic blood pressure 22 years later.
People who had high levels of anxiety and depression at all three time periods had larger decreases in both systolic and diastolic blood pressure and were less likely to develop hypertension by year 22. The study could not explain why symptoms of combined anxiety and depression were associated with decreased in blood pressure. The significance of this study may be to spur more research into the mechanisms that underlie the association between mental states and blood pressure.
For more information visit biomedcentral http://www.biomedcentral.com/content/pdf/1471-2458-11-601.pdf