Blood pressure and risk of headache: a prospective study of 22 685 adults in Norway. (Paper).

Objectives: Prevalence studies of the association between blood pressure ond headache hove shown conflicting results. The aim was to analyse the relation between brood pressure and risk of headache in a prospective study.

Methods: A total of 22 685 adults not likely to have headache, had their baseline blood pressure measured in 1984-6, and responded to a headache questionnaire at follow up 11 years later (1995-7). The relative risk of headache (migraine or non-migrainous headache) was estimated in relation to blood pressure at baseline.

Results: Those with a systolic blood pressure of 150 mm Hg or higher had 30% lower risk (risk ratio (RR)=0.7, 95% Cl 0.6-0.8) of having non-migrainous headache at follow up compared with those with systolic pressure lower than 140 mm Hg. For diastolic blood pressure, the risk of non-migrainous headache decreased with increasing values, and these findings were similar for both sexes, and were not influenced by use of antihypertensive medication. For migraine, there was no clear association with blood pressure.

Conclusion: In the first prospective study of blood pressure and the risk of headache, high systolic and diastolic pressures were associated with reduced risk of non-migrainous headache. One possible explanation may be the phenomenon of hypertension associated hypalgesia, which probably involves the baroreflex system influencing nociception in the brain stem or spinal cord.

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In 1913, Janeway noted that migraine was common in subjects with arterial hypertension, (1) and since then the relation between blood pressure and headache has been examined in many studies. (2-26) There is a consensus agreement within the International Headache Society that chronic arterial hypertension of mild to moderate degree does not cause headache. (27) Most cross sectional studies performed in unselected populations have shown no association (negative or positive) between blood pressure and the prevalence of headache. (2-14) In some studies, however, a higher prevalence of headache (15-18) and migraine" (19 20) has been reported in hypertensive patients than among normotensive controls. Other studies have found a higher prevalence of hypertension among patients who have headaches (21-23) or migraine (24-26) than among headache free people.

In this prospective study of a large unselected population, we have examined the relation between blood pressure measured between 1984 and 1986, and the subsequent risk of developing non-migrainous or migrainous headache at follow up 11 years later (1995-7). We also assessed the cross sectional association between blood pressure and headache prevalence as estimated at follow up in 1995-7.

MATERIAL AND METHODS

In Nord-Trondelag County in Norway, two population based epidemiological studies have been performed (The HUNT studies). (28 29) The first investigation (HUNT-I) took place between 1984 and 1986, and the main topics included blood pressure, diabetes mellitus, and health related quality of life. The second investigation (HUNT-2) was carried out between 1995 and 1997; it was more extensive than the first, and among several topics, HUNT-2 included 13 questions related to headache. (29)

In HUNT-l (1984-6), all residents 20 years and older were invited to participate, and a detailed description of the study population has been given by Holmen et al. (28) Briefly, out of 85 100 eligible people, 77 310 (91%) answered the questionnaire that was sent with the invitation, and participated in a medical examination that included measurements of height, weight, blood pressure, pulse, and blood glucose. Blood pressure was measured according to a standardised method that has been described in detail elsewhere. (28) The participants were seated, and blood pressure was measured using a mercury sphygmomanometer after at least 4 minutes rest with the cuff placed on the right upper arm. The cuff was inflated twice with an interval of at least 1 minute. Systolic and diastolic pressures were registered to the nearest 2 mm Hg, and the second measured pressure was used in the analysis of this study.

The HUNT-1 questionnaire did not include headache items, but 59 471 persons responded to a question on use of analgesics ("How often have you taken pain relieving medication during the last month?"). A total of 41 581 responded that they "never" used analgesics. For the purpose of the present study, we have assumed that among those who had never used analgesics, the proportion of those with headaches would be negligible. Among the 41 581 subjects, 22 720 also attended HUNT-2 and responded to the …