If you are elderly and your blood pressure suddenly drops, you could be in the initial stages of Alzheimer's disease or some other form of dementia, say scientists in Sweden. They found that if your systolic blood pressure fell at least 15 points in less than six years you had three times the risk of developing some kind of dementia. Systolic blood pressure is the top number.

The research was carried out at the Karolinska Institutet, Stockholm, Sweden.

Study leader, Dr. Chengxuan Qiu, said "Our findings imply that poor blood flow in the brain, resulting from an extensive decline in blood pressure, may promote the dementia process. These findings indicate a possible threshold level in systolic pressure, especially for people with vascular disease in whom further reduction of blood pressure under this level may precipitate dementia onset. Using antihypertensive medications is important for high blood pressure and related disorders, but our findings suggest that it is necessary to monitor these drugs in the very old to avoid a probable dangerous drop of blood pressure under a certain threshold."

You can read all about this study and its findings in the journal Stroke.

The scientists studied 947 people, they were all more than 75 years old and had never had any symptoms of dementia (or anything to indicate dementia onset). They were examined on three occasions - initially, three years later, and then again three years after that.

147 of them had Alzheimer's while another 39 had some other form of dementia after three years. Three years after that another 91 had Alzheimer's while 27 had other dementia.

Dr. Bengt Winblad, one of the team, said "Our data show no substantial differences in blood pressure levels at enrollment between non-demented persons and those that were demented three to six years later. However, some elderly people who experience a significant decline in systolic blood pressure three to six years before diagnosis do have an increased risk of dementia and Alzheimer's disease."

The scientists wondered whether the cells in the brain that regulate blood pressure were being degenerated. If so, perhaps low blood pressure may be one of the symptoms of dementia onset.