Data from a large human trial has shown that control of blood pressure in older individuals, achieved through lifestyle changes and medication, reduces the risk of mild cognitive impairment by 20% or so, but not the risk of dementia. This is a nuanced result; given what is known of the way in which blood pressure interacts unfavorably with a range of mechanisms related to the development of dementia, it is certainly easier to blame the study design, as the authors do here. There is plenty of evidence to show that hypertension damages the brain directly, causing a greater incidence of ruptured capillaries and tiny areas of dead tissue. It may also cause removal of metabolic waste to decline, contributing to the buildup of protein aggregates that progressively impairs the operation of the mind. It may change the behavior of immune cells in the brain for the worse. Further, the epidemiological data also exhibits a very good correlation between hypertension and dementia. So on the whole, the outcome of this study is a puzzle, and doesn't fit well with the established data on the subject.
Intensive lowering of blood pressure did not significantly reduce dementia risk but did have a measurable impact on mild cognitive impairment (MCI), according to the final, peer-reviewed results from the Systolic Blood Pressure Intervention Trial (SPRINT) Memory and Cognition in Decreased Hypertension (SPRINT MIND). SPRINT MIND secondary results are the first to show an intervention that significantly reduces the occurrence of MCI, which is a well-established precursor of dementia. MCI is a condition in which people have more difficulty with cognition, thinking, remembering, and reasoning, than normal for people their age. Dementia is a more severe form of loss in cognitive functions that interferes with daily life. Alzheimer's disease is the most common type of dementia. High blood pressure, or hypertension, is very common in persons over the age of 50 and a leading risk factor for heart disease, stroke, kidney failure, and a growing body of research suggests that it may increase risk for dementia later in life.
The participants in SPRINT were adults 50 years and older at high risk for cardiovascular disease. Results of the SPRINT trial, which ended early, showed that intensive blood pressure control, i.e., a systolic blood pressure target of less than 120 mmHg, compared to a standard target of less than 140 mmHg, reduced cardiovascular events and overall mortality. Between November 2010 and March 2013 more than 9,300 participants were randomized to the two target groups with nearly 4,700 in each group. In August 2015, the SPRINT trial was stopped after 3.3 years of treatment when the major beneficial effects of intensive blood pressure management on mortality and cardiovascular disease were discovered. Assessment for development of dementia and MCI continued for the full planned five years.
SPRINT MIND aimed to address whether intensive blood pressure control would also reduce the risk of developing dementia and cognitive impairment over the ensuing five years. Cognitive assessments were given to participants who had high blood pressure but no history of stroke or diabetes at the start of the trial, and over 91 percent had at least one follow up. Participants were classified into one of three categories: no cognitive impairment, MCI, or probable dementia.
The primary results of this analysis found no statistically significant difference between standard and intensive treatment in the proportion of participants that were diagnosed with dementia. The study, however, had fewer cases of dementia than expected. Nevertheless, the secondary results suggested that the intensive treatment reduced the risk of MCI and the combined risk of MCI and dementia. Due to the success of the SPRINT trial on the cardiovascular outcomes, the study intervention was stopped early; as a result, participants were treated for a shorter period than originally planned. The authors concluded that the shorter time and the unexpected fewer cases of dementia may have made it difficult to determine the role of intensive blood pressure control on dementia.