. >> reporter: emily flores had high blood pressure. she got it down but her doctor said not low enough. >> i decided i do want to live a better life. i needed to do this now. >> reporter: a blood pressure reading of 120 over 80 or lower is considered normal. anything above 140 over 90 is high. several years ago doctors created a third category -- prehypertension -- for everyone in between. how dangerous is prehypertension, especially the range just below high blood pressure? >> the study out today suggests that slightly lower blood pressure numbers may be incredibly harmful for your health. >> reporter: people at the low end of the prehypertension range have a 22% higher risk of stroke. those at the higher end of the range are 79% more at risk. specialists say that blood pressure is a continuous line with no magic point where it becomes dangerous. other factors including smoking, weight, exercise and diet influence how dangerous it is. the latest study is one more reason for caution. >> when your patients hear about this, how would you