Two new reports have caused a bit of a stir regarding blood pressure.  The first, a recent study has determined that 100 million Americans may be misclassified as having high blood pressure (hypertension).

Researchers from the University of Leuven in Belgium analyzed laboratory (urine samples) information obtained from almost 3,700 people at the beginning of the study, none of whom had heart disease, and two-thirds of whom had normal blood pressure. All participants were assigned to either a low-salt, moderate-salt, or high-salt diets, and were followed for eight years.

Approximately 25 percent of all participants, regardless of their group assignment, eventually developed high blood pressure during or at the completion of the study. Overall, there were no statistically significant differences observed between the salt intake groups, other than a slight increase in systolic blood pressure among those in the high-salt groups. But researchers noted the elevation was so small that it is probably insignificant.

"It's clear that one should be very careful in advocating generalized reduction in sodium intake in the population at large," stated Dr. Jan Staessen, author of the study. "There might be some benefits, but there might also be some adverse effects."

Dr. Brent Taylor from the Veterans Affairs Health Care System in Minneapolis and the University of Minnesota and his colleagues conducted a study that was published in the Journal of General Internal Medicine.

Their study discovered  that people are not actually more likely to die prematurely than those with 'normal' blood pressure, i.e. below 120/80.

The study found that in people under 50 years of age, diastolic blood pressure, the lowest pressure within the bloodstream, occurring between heart beats i.e. when the heart relaxes. Systolic blood pressure is the highest pressure within the bloodstream, occurring during each heart beat i.e. when the heart contracts.

Diastolic blood pressure is the more important predictor of mortality.  While people over 50, the systolic blood pressure is the stronger predictor. The authors suggest it is time to redefine ‘normal' blood pressure.

The researchers evaluated the independent contribution of diastolic blood pressure (DBP) and systolic blood pressure (SBP) on death, and  how these relationships might affect the number of Americans currently identified  as having abnormal blood pressure.

The researchers reviewed the data for 13,792 people from the National Health and Nutrition Examination Survey, which enrolled participants in 1971-76 and followed them up for two decades -- they studied their blood pressures (systolic and diastolic) and long-term survival data specifically. In order to assess the underlying distribution of untreated blood pressure in American adults by age, Taylor and team also looked at data for 6,672 adults from the first National Health Examination Survey conducted  between 1959 and 1962.

They found that in people aged over 50, those with SBPs above 140, independent of DBP, were significantly more likely to die prematurely. In those aged 50 or less, DBPs above 100 were linked to significant increases in premature death. The authors' analysis offers alternative cut-off points for the definition of 'normal'.

Dr. Taylor concludes: "Our findings highlight that the choice of approach used to define normal blood pressure will impact literally millions of Americans. If we cannot reliably see an effect on mortality in a large group of individuals followed for nearly 20 years, should we define the condition as abnormal? We believe considering this kind of approach represents a critical step in ensuring that diagnoses are given only to those with a meaningful elevation in risk, and targeted towards individuals most likely to benefit."

This study is very important, because not only are tens of millions of people taking blood pressure unnecessarily.  Anti-hypertensive medications have numerous side effects that are apparently, according to this study happening in people who don’t need to take the medication.

Salt Study Challenges High Blood Pressure and High Salt Intake Link

I just recalled a statement made to my during my rotation on the kidney service (nephrology) by one of my professors.  She said that there was a lot more to hypertension than salt. I never forgot her wise words.  A few days ago, I ran across a study that supports her thoughts. It was conducted in Belgium and reported in the Journal of the American Medical Association challenges accepted, conventional wisdom about heart health and salt intake, indicating that high levels of salt intake, don’t always cause hypertension and cardiovascular disease.

At the study’s end, the researchers noted that there was no difference in the rates of high blood pressure and heart disease among the three groups.  Interestingly, and quite surprising to the researchers, only one percent of the high-salt group died from heart disease, while four percent of those in the low-salt group died due to complications of heart disease.  This finding suggests that low-salt diets may actually be more of a health risk than high-salt diets.

Sources:

http://www.sciencedaily.com/releases/2011/03/110309101807.htm

http://jama.ama-assn.org/content/305/17/1777.short

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