Blood pressure and headaches, Part 1

The question of how headaches and high blood pressure relate to each other has a long tradition in medical research. Even today, the results in this field are very inconsistent and continue to give rise to lively debate among specialists. Particularly in cases where an “association” between headache and high blood pressure is assumed, there is often a lack of detailed analysis of the underlying pathomechanisms. As ever, we must remember that we cannot infer an underlying causality based on correlation; the simultaneous occurrence of hypertension and headaches does not necessarily mean that there is a causal link. And even if there is: how can we determine what is cause and what is effect with the methods available to us today?  This article presents the most important findings in contemporary research and gives an insight into the most exciting questions of future development in the field.

Comorbidity between headaches and high blood pressure: what exactly do we know?

Various studies in more recent research describe a comorbidity between headaches and high blood pressure. This means that they state that headaches and high blood pressure occur simultaneously in patients. Depending on how the study is designed, the composition or size of the group of affected people being examined, and the particular type of headache, the results of the sometimes extensive studies vary. Therefore, different surveys reach different conclusions regarding for example, how high the percentage of patients is who suffer from high blood pressure as well as headaches, and vice versa.

The question of question direction: from high blood pressure to headache or the reverse?

Turning our attention to migraine, we can see how different studies are trying to map the comorbidity of headache symptoms and high blood pressure in different ways. One study in Finland medically monitored people with migraine over a period of five years, while recording different health parameters. After this period, they found that people with migraine had a significantly higher risk of developing high blood pressure than the control subjects. (However, as a limitation of these findings’ validity, it must be noted here that the migraine diagnosis was declared by the participants themselves and not tested anamnestically).

In the Finnish study, researchers were therefore asking whether people with migraine experience high blood pressure more frequently than the healthy population. To a certain extent, a New York study did the opposite; here, they discovered that out of the 1,300 observed participants – who had an average age of 68 – 76% had high blood pressure. Again, there was a significantly higher rate of migraine with and without aura in this group. The comorbidity was especially pronounced when the high blood pressure was untreated or had persisted over a longer period (> 9 years).

Correlation ≠ Causation

Based on these kinds of studies, we gain an indication of whether and to what extent (certain) headache disorders occur at the same time as high blood pressure for affected people. However, the exact connection between headache symptoms and high blood pressure – which mechanisms are responsible for the fact that both occur simultaneously and whether, for example, one illness is causal for the other – cannot be determined so easily.

Is there a causality of comorbidity?

An Italian-French paper from 2013 provides an approach to potential mechanisms of how high blood pressure can develop, especially for people with migraine, and which factors could contribute to this. It reports that there are often pathologic changes to the blood vessels of migraine patients. Consequently, there is a hardening/stiffening of the vascular walls, which impairs their flexibility. This makes important regulatory processes (e.g., tightening or widening the vessels), with which the body sets and adjusts the blood pressure (key word: disturbed homeostasis), more difficult. Moreover, the vascular endothelium (the layer of cells, which lines the inside of the vessels) becomes damaged, which can also affect flexibility and the response to regulatory messenger substances. The author reports that the findings are also relatively consistent with regard to the large arteries in the body, according to which the regulatory processes here are also impaired for people with migraine.

The evidence is growing: the blood vessels in the brains of people with migraine

A Polish investigation from 2015 confirms the theory of the impaired vascular endothelium for people with migraine; the authors find functional impairment of the blood vessels in the brain and damaged endothelia. They point out that the risk of stroke is also higher with migraine. Furthermore, they discover brain areas with a low blood supply with so-called ischaemic lesions (damage which is caused by an insufficient supply of blood/oxygen) – presumably as a result of vessel damage. This paper also points out that changes to the blood-brain barrier can occur in the context of “cortical spreading depression” (the wavelike excitation propagation during an attack). Consequently, the affected areas could suffer from an insufficient blood supply, further worsening the impairment due to the migraine attack.

However, whether the pathologic changes described above are limited to the area of the head or whether the whole body is affected (particularly keeping in mind the blood vessels), has not yet been conclusively resolved.

The next part of our two-part series on blood pressure and headaches will appear next month. There, we will take a look at the connection between high blood pressure and altered pain perception, consider its evolutionary purpose, and take a look at the future of research.