A recent study in older people suggests that reducing blood pressure to levels below the usual standard can lessen the risk of mild cognitive impairment, which is a condition that often precedes dementia.

Scientists at the Wake Forest School of Medicine in Winston-Salem, NC, led a randomized clinical trial involving just under 9,400 adults in their 50s or older with high blood pressure. The objective of the trial, as the investigative team notes in the JAMA study paper, was to "evaluate the effect of intensive blood pressure control on risk of dementia."

The older adults received either intensive blood pressure control or standard treatment. The purpose of intensive control was to bring systolic blood pressure below 120 millimeters of mercury (mm Hg), while that of standard treatment was to lower it to under 140 mm Hg. Systolic blood pressure is the pressure in the arteries when the heart contracts. It is usually the first number in a blood pressure measurement, as in "140/80 mm Hg," for instance.

The results revealed that significantly fewer of those who received intensive blood pressure control went on to develop mild cognitive impairment (MCI), compared with those on the standard treatment.

"In the study," says lead investigator Dr. Jeff D. Williamson, who is a professor of gerontology and geriatric medicine at the Wake Forest School of Medicine, "we found that just 3 years of lowering blood pressure not only dramatically helped the heart but also helped the brain."

The trial did not show the same result for dementia: Intensive blood pressure control did not reduce the incidence of dementia, compared with standard control. Dr. Williamson comments that while there was a "15% reduction in dementia in the intensively controlled group, we were disappointed that the results did not achieve statistical significance for this outcome." However, the authors suggest that low numbers and the study finishing earlier than planned could be reasons for this.

Dementia and MCI

Dementia is a general term for illnesses that affect the brain and in which there is a decline in behavior, thinking, memory, and the ability to carry out everyday tasks. Alzheimer's, which is a disease that progressively destroys brain tissue, is the main cause of dementia. According to the World Health Organization (WHO) around 60%–70% of the 50 million people worldwide who are living with dementia have Alzheimer's. Many people who have a disability or who cannot care for themselves have dementia. Although it typically affects older people, it is not a normal consequence of aging.

MCI is a condition in which the affected individuals and the people around them notice some loss of mental capacity. This can include, for example, forgetting important appointments, losing the thread of a conversation, and having difficulties reasoning and making decisions. However, the changes that occur with MCI are not so severe that they prevent the person from taking care of themselves and getting on with everyday life.

MCI affects around 15%–20% of those aged 65 or older. Having MCI raises the risk of developing dementia, especially if the symptoms suggest problems with memory. Not everyone who has MCI, however, will develop dementia. The condition can remain stable or, in some cases, even reverse. Experts are not sure what causes MCI but strongly suspect that many cases are due to changes in the brain wrought by diseases such as Alzheimer's and other forms of dementia. Being of older age, having a family history of dementia, and having conditions that increase the risk of developing cardiovascular disease are the strongest risk factors for MCI. There are currently no approved drugs in the US for the treatment of MCI. Also, drugs approved for the relief of Alzheimer's disease have not done much to stop or prevent MCI from progressing to dementia.

Degrees of blood pressure control

High blood pressure affects more than half of those over 50 and more than three-quarters of those over the age of 65. Previous studies that have followed groups of people over time have suggested that blood pressure is a "modifiable risk factor" for dementia and MCI.

The investigation that Dr. Williamson and colleagues undertook was part of the Systolic Blood Pressure Intervention Trial (SPRINT) run by the National Institutes of Health (NIH). The data came from 9,361 individuals aged 50 or older whose systolic blood pressure was at least 130 mm Hg. They all had at least one further risk factor for cardiovascular disease but no history of stroke, diabetes, or polycystic kidney disease.

Recruitment took place between 2010 and 2013 at 102 centers in the US, including Puerto Rico. The average age of the cohort was 68 years, 28% of the cohort were aged 75 or older, 35.6% were female, 30% were African-American, and 10.5% were Hispanic.

Intensive control reduced MCI risk

The trial randomly assigned 4,678 participants to the intensive treatment group and 4,683 to the standard treatment group. After 5 years, following tests and assessments that included "expert adjudication for dementia and MCI," the researchers classified individuals as having "probable dementia," MCI, or no MCI.

Of these, 149 participants who developed probable dementia had received intensive treatment, compared with 176 who had received standard treatment. These figures equate to 7.2 and 8.6 cases for every 1,000 person-years, respectively. The authors conclude that, based on this evidence, intensive treatment to reduce high blood pressure in older adults to below 120 mm Hg systolic does not significantly reduce the risk of dementia.

For MCI, the analysis revealed that intensive control of blood pressure "significantly reduce[s] the risk." The rates here were 14.6 and 18.3 cases for every 1,000 person-years, for intensive control and standard treatment, respectively.

The authors note that, because of the cardiovascular benefits of intensive blood pressure control, the trial finished earlier than planned. This early termination, together with "fewer than expected cases of dementia," probably made it difficult to accurately assess the impact of intensive control on the incidence of dementia.

"As doctors treating older patients, we are encouraged to finally have a proven intervention to lower someone's risk for MCI."

—Dr. Jeff D. Williamson