Most studies on blood pressure (BP) have focused on high BP, whereas studies on low BP are rare. Unlike hypertension, constitutional low BP is not considered to be related to serious illness or death, and it is widely accepted that ‘the lower the BP, the better’.
However, it was not difficult to find people who complain, ‘I’m dizzy because my blood pressure is low’ or ‘I feel down because of my low blood pressure’. This raised our suspicions about the common perception that low blood pressure is not really a problem, and thus marked the beginning of our research.
Using data from the 2010-2013 Korea National Health and Nutrition survey, we compared 10,708 people with either normal or low blood pressure. Suicidal ideation was identified by asking one of two questions: “Have you ever felt inclined to commit suicide over the last year?” (2010-2012) and “Have you ever considered suicide seriously over the last year?” (2013).
The results showed that among people with normal blood pressure, the proportion of those with suicidal ideation was 10.8%. This proportion increased for people with lower blood pressures: those with systolic blood pressure (SBP) <100 mmHg the proportion was 12.5%; those with SBP <95 mmHg, 13.7%; and those with SBP <90 mmHg, 16.6%. In other words the lower the blood pressure, the higher the percentage of people with suicidal thought. Observing the distribution of low blood pressure among those with suicidal thought and those without, we came to the following assumption: Low blood pressure may explain a higher risk of suicidal thought.
Observing the distribution of low blood pressure among those with suicidal thought and those without, we came to the following assumption: Low blood pressure may explain a higher risk of suicidal thought.
We then analyzed the risk of suicidal ideation present in people with low blood pressure after controlling for potential confounding variables such as gender, age, BMI and underlying diseases. As a result, people with a systolic blood pressure lower than 100 mmHg were shown to have more than 25% higher odds of suicide ideation than those with normal blood pressure.
We also found that increasing the strictness of the criteria for low BP led to a more pronounced tendency towards suicidal ideation. That is, the odds of suicidal ideation for the low blood pressure group with a cut-off value of SBP< 95 mmHg and SBP <90 mmHg was 43% and 74% higher, respectively, than that of the normal pressure group.
In addition to looking at low blood pressure, we also investigated the risk of suicidal thought at high blood pressure. However, there were no statistically significant differences between the risk of suicidal ideation among the higher blood pressure groups (pre-hypertensive and hypertensive) and that of the normotensive group. Therefore, low blood pressure may pose its own different health issues in comparison to high blood pressure. Our study hereby challenges the perception that, in terms of mental health, lower blood pressure is always better.
Nevertheless, this study is a cross-sectional study and cannot verify the causal relationship between low blood pressure and suicidal ideation. The study’s use of self-reported survey data may have introduced information and recall bias. As only levels of systolic blood pressure were used to define low blood pressure, future studies are needed to explore the relationship between suicidal ideation and diastolic blood pressure. Further research is also needed into the possible biological mechanisms that may explain the association between blood pressure and suicidal ideation.
This study is the first to investigate the association between low BP and suicidal ideation, which is an indicator of a negative psychiatric state, and thus underscores the need to re-evaluate the health implications of low BP. This may also call for careful monitoring of the mental health conditions of those with low BP.