For the past several years, cardiologists have been beating the drum for lower blood pressure. We have all seen the studies and/or articles that have challenged the notion that the old cut-off of 140/90mmHg is too high for diagnosing high blood pressure. The medical community even went so far as to coin the new term "pre-hypertension" to describe individuals with a blood pressure over 120/80mmHg. Now, a review of data from an old study could change a few minds - there may a limit to the "lower is better" thinking - at least when it comes to blood pressure.
Researchers recently reviewed blood pressure data from the 2005 Treating to New Targets (TNT) study which, interestingly enough, was designed to determine if the "lower is better" philosophy applied to lowering LDL cholesterol. What they found was intriguing. As participants lowered their blood pressure they did indeed decrease their risk of cardiovascular death - but only up to a point. The data showed that blood pressure below 110/60mmHg created a pronounced increase in cardiovascular mortality. This finding is similar to what was uncovered in the INVEST trial (which had absolutely nothing to do with heart disease but luckily blood pressure is commonly recorded in most trials and can be reviewed years later to produce new findings).
What researchers seemed to discover about blood pressure and mortality is that it exhibited what is what is known as the "J-curve" effect. Initially, mortality is reduced as blood pressure drops but there appears to be a point of diminishing returns. If blood pressure drops too low you actually stand a greater chance of dying from cardiac events. Of course, the big question is, "Why?"
Common sense tells us that there must be some point at which a continued reduction in blood pressure will be harmful. Some scientists even joked that "After all, if blood pressure is zero, mortality is 100%." But what could account for this turnaround at blood pressures as common as 110/60mmHg?
- Lower blood pressure may lead to lower perfusion of the heart. As perfusion decreases the heart receives less oxygen and increases heart attack risk.
- Lower diastolic blood pressures result in higher pulse pressures causing endothelial dysfunction, stiff arteries, and, eventually, more heart disease.
- Low blood pressure might simply be a surrogate for other disease states and not a cause itself. People with lower blood pressure may have been already sicker than those with higher blood pressure and naturally died more often. Low blood pressure did not cause increased mortality, rather, it was merely an indicator of a imminent death.
The last explanation could easily be the entire explanation for this statistical paradox. Researchers did not prove the lower blood pressure caused mortality to rise; they only noted that the two are associated. For example, every time a plane flies over my backyard, my dog barks at it. Every time my dog barks at a plane it continues to fly away and does not land in my backyard. Therefore, while I can say my dog's bark is ASSOCIATED with planes not landing in my backyard, I cannot say my dog's bark CAUSED the plane to fly away." Barking dogs clearly scare away postmen, robbers, cats, and rabbits but not airplanes even though from, a statistical association standpoint, the observations may be identical. In fact, I think we can all agree it was probably the plane that caused the dog to bark!
In short, while the findings are interesting and may suggest more research is called for I would not stop taking my blood pressure medicine. We already know that there are many other reasons for not letting blood pressure get too low - death notwithstanding. Also keep in mind that blood pressure changes often during the day. One lower reading should not be cause for alarm.
My readers know I do not hold the traditional medical establish in any great awe but, in this case, my advice is to discuss your blood pressure with your doctor if you think it may be too low. There are plenty of other reasons to make needed adjustments to blood pressure beyond the interesting, yet unproven, causal connection between lower blood pressure and increased mortality.
Looking out for your heart health,
Published On: May 12, 2009