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COPENHAGEN -- Among individuals who developed hypertension at age 90 or later, their risk of also developing dementia was dramatically lower than other very elderly people whose blood pressure remained normal, researchers said here.

With mean follow-up 2.8 years (range up to 10 years), the age- and education-adjusted relative risk of incident dementia in 625 prospectively followed individuals was 0.45 (P<0.01) for those with onset of hypertension in their 90s, compared with similarly aged participants remaining hypertension-free, reported , of the University of California Irvine.

In fact, among individuals surviving to age 90, hypertension was clearly not a risk factor for dementia no matter when it began, Corrada said at a press briefing held prior to her formal presentation at the Alzheimer's Association International Conference.

Although cardiovascular abnormalities including hypertension have previously been linked to increased dementia risk, those studies primarily involved onset of elevated blood pressure in young adulthood and middle age. Corrada noted that the evidence has suggested that the association is not uniform across all age groups, prompting a focused look at the very old, who are becoming increasingly numerous.

The study sample consisted of surviving participants in the 14,000-participant Leisure World Cohort Study, which began in 1981. In 2003, a was commenced for Leisure World Cohort Study members who had lived to age 90 and beyond. The current analysis was restricted to 625 participants who did not meet DSM-IV criteria for dementia.

While in the 90+ Study, participants were evaluated for hypertension and dementia (among other exams) at clinic visits every 6 months. Onset of hypertension prior to 2003 was determined from patient self-reports while participating in the Leisure World study.

At enrollment in the current study, the mean patient age was 93. During follow-up there were 259 cases of incident dementia.

Participants who developed hypertension while in their 80s also had a lower risk for dementia compared with those with normal blood pressure (relative risk 0.59, P<0.05). Those with hypertension first diagnosed or reported earlier -- even prior to age 70 -- - showed no significant increase in dementia risk, Corrada indicated.

The severity of hypertension was also associated with reduced risk. Participants with systolic pressure of 160 mm Hg or higher, or diastolic pressure of 100 mm Hg or more, had a relative risk of 0.58 (P=0.05) compared with participants with systolic pressure below 120 mmHg or diastolic pressure below 80 mm Hg (these values were adjusted for age, education, and use of antihypertensive medications).

Lesser degrees of hypertension were commensurately associated with a lesser decrease in dementia risk. At the press briefing, Corrada showed an almost perfectly linear trend line connecting the point estimates for relative dementia risk in four categories of blood pressure, with a P-value of 0.05.

She suggested that development of hypertension "at older ages may be beneficial for maintaining intact cognition" -- perhaps by preserving blood flow and oxygenation in the brain.

Corrada also argued that this potential benefit of high blood pressure should be taken into account when clinicians consider the treatment options for new-onset hypertension in the very elderly.

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