A recent Cochrane Review investigated whether lowering blood pressure below 140/90mmHg was beneficial in prolonging survival or reducing stroke, heart attack, heart failure or kidney failure. Surprisingly, they concluded that, “More trials are needed, but at present there is no evidence to support aiming for a blood pressure target lower than 140/90 mmHg in any hypertensive patient.”! They also mentioned that this held true for high risk patients (such as diabetics) as well.

You can read the report here: http://mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD004349/frame.html.