People whose blood pressure varies widely from day to day may be more likely to develop dementia than adults who have fairly steady blood pressure, a Japanese study suggests.
Researchers examined data from one month of daily home blood pressure readings for 1,674 older adults without dementia. During the next five years, compared to individuals with little to no fluctuation, people with the most variations in blood pressure were more than twice as likely to develop dementia.
"The present study demonstrated that an increased day-to-day blood pressure variation (measured at home) was significantly associated with the development of all-cause dementia, vascular dementia, and Alzheimer's disease, regardless of average home blood pressure," said lead study author Dr. Tomoyuki Ohara, of the Graduate School of Medical Sciences at Kyushu University in Fukuoka City.
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While the study didn't assess why this might be the case, it's possible that daily variation in blood pressure might cause changes in the brain's structure and function that contribute to the development of dementia, Ohara said by email.
Consistently high blood pressure, or hypertension, is a known risk factor for dementia. Previous research has also shown a link between cognitive impairment and dementia and different blood pressure readings at the doctor's office.
Home monitoring might give a more reliable snapshot of blood pressure than tests at the doctor's office because stress or anxiety about these exams sometimes leads patients to have higher blood pressure at the office than they do at home, a so-called "white coat" effect.
Participants measured blood pressure over 5 years
Participants in the current study were 71 years old on average. For one month, they typically measured their blood pressure three times each morning before eating breakfast or taking medication. About 43 per cent of them took drugs to manage high blood pressure.
Researchers reviewed data from blood pressure readings taken during that month, conducted cognitive testing to uncover the development of dementia, and reviewed medical records for the occurrence of stroke.
Five years later, 134 participants had developed Alzheimer's disease and 47 had developed what's known as vascular dementia, which results from diminished blood flow to the brain and is often related to the occurrence of small strokes.
People with the most variation in daily blood pressure readings at the start of the study were more than twice as likely to develop Alzheimer's disease and almost three times more likely to develop vascular dementia, researchers report in Circulation.
Among participants with the most variability in blood pressure, higher systolic blood pressure (the top number in a blood pressure reading) in particular increased the risk of vascular dementia but didn't appear to heighten the odds of Alzheimer's disease. Systolic pressure is the pressure blood exerts against artery walls when the heart beats.
One limitation of the study is that researchers lacked data on changes in blood pressure after the initial home monitoring period and didn't have information on any lifestyle changes or medications people may have used to control blood pressure during the five-year follow-up period, the authors note.
It's also possible that fluctuations in blood pressure could be a symptom of cognitive decline in progress rather than a risk factor for developing dementia in the future, Dr. Costantino Iadecola, director of the Feil Family Brain and Mind Research Institute at Weill Cornell Medicine in New York writes in an accompanying editorial.
'Maintaining general cardiovascular health through lifestyle changes (diet, exercise, etc.) and control of risk factors ... remain the most sensible approaches to stave off dementia.' - Dr. Costantino Iadecola
Iadecola noted that, presently, doctors don't know how to reduce variability in blood pressure.
"The key question to be answered is whether interventions to control blood pressure variation, once available, would reduce dementia risk," he said by email.
"In the meantime, the take-home message is that the health of the cardiovascular system is of paramount importance to the health of the brain," Iadecola added. "Even if specific measures to target blood pressure variation may not be available at this time, maintaining general cardiovascular health through lifestyle changes (diet, exercise, etc.) and control of risk factors (diabetes, hypertension, smoking, obesity, etc.) remain the most sensible approaches to stave off dementia."