In this large epidemiological study, we found that low blood pressure was associated with increased prevalence of anxiety and depression. The associations were independent of age, sex or cardiovascular disease, and our sample size makes it likely that any effect modification by these factors would have been discovered. This is the first time that these common mental disorders have been clearly linked to low systolic and diastolic blood pressure in a large, community‐based population. The large sample size gave us an opportunity to examine the whole blood pressure distribution, and showed that the lowest centiles were associated with the highest prevalence of anxiety and depression.
Four of six geriatric studies reported an association of low diastolic blood pressure with depression,13,15
or of both diastolic and systolic blood pressure with depression.6,14
In one of these studies, no association was found; however, high diastolic blood pressure seemed to predict fewer cases of depression 3 years later.16
Increased “negative affect”, which was recognised as a common feature of both anxiety and depression in one of the geriatric studies, was not found to be associated with low blood pressure.15
Compared with these studies, our study is the first to report an association also with anxiety, and to show that these associations are not only seen in old age. Other studies have reported positive associations between hypertension and anger, anxiety and depression. However, psychometric properties of the scales used in these studies have often been less well established.9
In our study, hypertension was not associated with anxiety or depression, except for the upper five centiles of systolic blood pressure, which had significant lower OR for comorbid anxiety and depression compared with the reference group (table 3). Our results are in contrast with a recent study among poor, elderly people from rural China, where an association between undetected hypertension and depression was found.17
In the multivariable analyses, the most important finding was that adjustment for several covariates reduced the effect sizes only moderately. Physical impairment, owing to somatic disease or movement restriction, had the strongest effect on the associations. Low blood pressure might partly be a result of immobility due to physical impairment, but the variable “physical activity” had no adjusting effect. In addition, depression, and possibly also anxiety, could result in overestimation of somatic health problems. Therefore, it is difficult to assess if physical impairment had a mediating effect on the associations or represented some type of information bias. Smoking was the second most influential covariate. Activation of cerebral nicotinergic receptors is reported to have effects on anxiety and depression,24
and adverse haemodynamic effects.25
However, the influence of nicotine on the relationship of low blood pressure with anxiety and depression is probably quite complex.
In our study, use of drugs for hypertension did not influence the association of low blood pressure with anxiety and depression. This is in line with geriatric studies finding no effect of drugs against hypertension on the association between low blood pressure and depression.13,14,15
Similarly, previous studies also found that antidepressants did not influence this association.6,13
In our sample, 2.9% of participants reported using drugs for depression during some part of the year before the survey; at the time of the blood pressure measurement, about half of these were currently using drugs for depression. As the use of drugs for depression is an alternative measure of depression besides the HADS, we did not include the use of antidepressants due to the risk of over‐adjustment. However, the association was maintained, although weakened, when people using drugs for depression were excluded from the analyses.
The strengths of this study are the examination of the whole adult population within a geographical area that is fairly representative of Norway, and with a high participation rate19
; the standardised assessment of blood pressure, and symptoms of anxiety and depression; the exploration of the whole blood pressure range; and the multivariable analyses with adjustment for several factors, of whom many are known to influence blood pressure, and anxiety and depression.
It might be argued that in this study, the blood pressure measurement, and to a lesser degree the HADS, give only a “snap‐shot” of the participants' situation. In epidemiological studies, however, screening measurements, and not clinical diagnosis, are the standard. Statistically, slightly reduced validity of measuring either blood pressure or mental symptoms would weaken rather than strengthen any association between them. Clinically, anxiety often increases blood pressure at measurement,26
making it unlikely that this “white coat effect” could strengthen the association with low blood pressure. Therefore, measurement bias may probably not explain the observed associations.
Previously, medicine regarded the association between low blood pressure and mental symptoms as part of a “constitutional hypotension” or a “hypotensive syndrome”. A “hypotoner symptomenkomplex” is still mentioned in a new German textbook.27
In English‐speaking countries, from 19402
until now, the dominant attitude has been far more unanimous: chronic low blood pressure does not produce symptoms. Several papers have reflected this controversy: a study in 1997 found no link between low blood pressure and psychological dysfunction or fatigue, and questioned the findings in earlier studies.18
In the same year, however, other authors asked if hypotension was a forgotten illness.28
Since then, studies have linked low blood pressure to depression,6,14,15
higher risk of dementia in elderly people30
and the development of chronic fatigue.31
What mechanisms could be involved in the relationship of low blood pressure with anxiety and depression? Neurones that control blood pressure are reported to express neuropeptide Y; this peptide seems to reduce both blood pressure and anxiety, and lowers the sympathetic outflow.32
Neuropeptide Y is only one of a large number of neurotransmitters or neuromodulators that are involved in different stress responses. Two main systems play a pivotal part: the hypothalamic–pituitary–adrenocortical axis and the renin–angiotensin system.33
The neuroendocrine mechanisms involved are most likely very complicated and only partly understood at present.
Our data give epidemiological evidence for an association of low blood pressure with anxiety and depression in adults, independent of age and sex. We want to underline that: (1) our findings could not be ascribed to lowering of blood pressure by the use of drugs for hypertension. In fact, people taking drugs for hypertension had higher blood pressure than the rest of the study participants, and the use of such drugs had no effect on the blood–pressure–mental disorder relationship. Thus, the results provide no argument for not treating hypertension adequately. (2) Neuroendocrine studies are needed to explore the mechanisms that might be involved in the association between low blood pressure and mental disorders, and further epidemiological studies are needed to clarify whether a more extensive hypotensive syndrome really exists.
- Low blood pressure was found to be associated with anxiety and depression in the general population.
- The associations were independent of sex or age groups.
- Cardiovascular disease or the use of drugs for hypertension did not explain the associations.
- Neuroendocrine studies are needed to explore the mechanisms that might be involved in the associations.