Blood pressure changes throughout the day, so it is normal to decrease by 10-20% at night compared to the day.

This is called a'dipping' of blood pressure, and a'reverse dipping' occurs in which the blood pressure at night, which should be lowered, becomes higher than during the day.

Research has shown that elderly people with a'reverse drop' in blood pressure are at higher risk of developing dementia.

A study conducted by Christian Benedict, a neuroscience professor at the University of Uppsala Medical School in Sweden, conducted a follow-up survey of 997 elderly people in their 70s for up to 24 years.

The researchers investigated the difference in blood pressure between day and night through 24-hour ambulatory blood pressure monitoring (ABPM) when they were 70 years old, and again measured their 24-hour blood pressure seven years later when they turned 77.

At the age of 70, 35% of them were taking blood pressure medications.

At the age of 77, only 611 of them participated, and 41% were taking blood pressure medications.

Researchers followed up to see if they developed dementia until they were 95 years old.

As a result, it was found that elderly people with higher peak blood pressure (systolic blood pressure) at night than during the day have a 64% higher risk of developing dementia.

Among the various forms of dementia, the risk of Alzheimer's dementia was 67% higher, and the increased risk of vascular dementia remained at 29%.

If the peak blood pressure at night was the same as that of the day or 10%, and the'lowering' of blood pressure at night was insufficient, it was not associated with an increased risk of dementia.

The results show that'reverse drop' blood pressure, which increases blood pressure at night rather than during the day, may be an independent risk factor for dementia, the researchers explained.

Therefore, it is necessary to study whether taking blood pressure pills before bedtime to lower blood pressure at night can prevent an increased risk of dementia in elderly people with'reverse-lowering' blood pressure, the researchers stressed.

The findings were published in the latest issue of Hypertension, the journal of the American Heart Association (AHA).