Low normal BP may increase risk in diabetics and high-risk patients

We’ve previously written in this column that despite what existing clinical treatment guidelines might say, many experts are now convinced with the results of recent studies showing that an aggressive blood pressure (BP) lowering is no longer ideal in high-risk patients including diabetics. The forthcoming clinical guidelines on treating high blood pressure are expected to be revised based on the results of these recent researches.

Previous guidelines recommend a BP goal lower than 130/80 mm Hg in diabetics and other high-risk patients. It was also deemed prudent to initiate antihypertensive therapy in high-risk patients even if their BP was still in the normal range like 130/85 mm Hg.

This aggressive antihypertensive approach and lower BP recommendation were based on the results of clinical trials published in the late ’80s and ’90s such as the United Kingdom Prospective Diabetes Study (UKPDS) and Hypertension Optimal Treatment (HOT) trial, which favored maintaining lower BP levels in high-risk patients over the conventional recommendation in the general population of a BP less than 140/90 mm Hg. At that time, this was supported by epidemiological studies suggesting that cardiovascular risk starts to increase above a BP level of 115/75 mm Hg, which was supposed to be the optimal or ideal BP. Then, hypertension experts thought that there is no lower threshold for BP lowering in high-risk patients, such that “the lower the BP, the better.”

Just like many long-held tenets in the ever-dynamic field of medicine, which is not an exact science as physics or mathematics, the recommendation of aggressive BP lowering is about to change.  Published researches in the last three years, such as the  Action to Control Cardiovascular Risk in Diabetes (Accord) study, showed no additional cardiovascular benefits of BP lowering in reducing systolic BP (SBP) below 130 mm Hg in diabetics. Other studies have also suggested that aggressive BP lowering to less than 120/90 mm Hg in high-risk patients might actually do more harm than good.

A study published very recently in the British Medical Journal looked into the association of systolic and diastolic BP (DBP) and deaths from all causes in people with newly diagnosed type 2 diabetes, with and without established cardiovascular disease (CVD).

After a median follow-up of 3.5 years, one-fifth of the patients under study had died already. In patients with known CVD, hence considered high risk, an SBP lower than 110 mm Hg was associated  with more deaths than those whose SBP was 130 to 139 mm Hg. The risk was increased 2.8 times. The chances of dying in patients with SBP of 110 to 129 mm Hg was similar to that in patients with SBP of 130 to 139. In patients with DBP of 70 to 74 mm Hg and those whose DBP was <70 mm Hg, there was a significantly higher mortality than those whose DBP was 80 to 84 mm Hg, with a risk of 1.3 and 1.9 times, respectively. A similar pattern of results was seen in patients without CVD.

The authors wrote in their conclusion: “Blood pressure below 130/80 mm Hg was not associated with reduced risk of all-cause mortality (deaths) in patients with newly diagnosed diabetes, with or without known cardiovascular disease. Low blood pressure, particularly below 110/75 mm Hg, was associated with an increased risk for poor outcomes.”

These findings again highlight the so-called J-curve phenomenon in blood pressure which shows that lowering elevated BP levels (more than 140/90 mm Hg) is beneficial up to a certain point (represented by the descending arm of the J), but lowering it excessively shows a paradoxical increase in harm or even death (represented by the short ascending arm of the J).

Based on recent clinical researches, maintaining a BP less than 140/90 mm Hg and somewhere in the range of 110/75 to 135/84 mm Hg would be ideal, especially in diabetics and high-risk patients. BP levels lower than this range may be courting harm.