The Danger of “Normal” Blood Pressure

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Those who have read “Salt Toxicity and Hypertension” (1)are aware this reviewer has long maintained that a physiologically normal blood pressure (BP) or the optimal BP level for humans is likely below 100/60 mmHg. Our closest biological relatives (chimpanzees, orangutans, bonobos, and gorillas) and likely our ancient ancestors all evolved on a diet with either little or no added salt. A study of chimpanzees showed they see their BP rise in response to a diet with a similar amount of salt found in a normal Western-style diet. A study of several isolated human populations consuming a diet with little or no added salt see their BP remain low throughout life (2). By contrast, in the US even people who make it to age 55y or 65y without developing HTN [140/90 or higher] still have about a 90% chance of developing HTN over the next 25 to 30 years (3). 

What about people who maintain what most MDs consider a perfectly “normal” BP into late middle age? New evidence now suggests that even for Americans who maintain what is now considered a “normal” BP into their late 50s and early 60s will still experience a markedly greater risk of atherosclerotic cardiovascular disease (ASCVD) even if their Systolic BP (SBP) stays below 130 mmHg.

Of course, most people will not be able to sustain their SBP of <130mmHg throughout life while consuming a diet that contains anything close to what most people consider a typical modern diet. There are many dietary factors that contribute to rise in SBP with age. The greatest of these controllable risk factors is the amount of added dietary salt. There is little doubt that what most people think of as a “normal” salt intake is all but guaranteed to contribute to the increase in BP (and especially SBP) seen in almost all people in modern societies. The impact of added salt can be modified by other dietary variables. However, altering other dietary variables besides salt or sodium intake will not eliminate the increasing SBP over time. For many years, MDs once considered increasing SBP with age a normal part of aging. Indeed, it led the medical profession to develop a simple formula for determining if a patient’s SBP was too high. That formula was SBP is fine provided the SBP is no higher than 100 + the patient’s age. Of course, that formula was long ago abandoned once data clearly showed elevated SBP is associated with far more morbidity and mortality regardless of age.

DASH Trials Show Diet Can Lower Elevated BP 

A DASH-style diet with more fruits, vegetables, whole grains, and less saturated fat has been shown to lower BP and SBP independently of salt intake, especially in those with HTN. But the DASH-Sodium Trial showed that by far the single most important factor for lowering SBP in those with Stage 1 HTN or even more modestly elevated SBP if the marked reduction in sodium to <1200mg/day, which is far below the average sodium intake for Americans. This was clearly shown in the DASH-Sodium trial that found that reducing sodium from 3300mg/day to 1200mg/day was at least as effective for reducing SBP as adopting the DASH diet without additional sodium restriction (4).

“Elevated SBP Promotes CVD Even in the “Normal” Range

A study published in the June 10, 2020 JAMA Cardiology examined the correlation between SBP and ASCVD in 1457 subjects from the Multi-Ethnic Study of Atherosclerosis (MESA) cohort. Initially all subjects had no evidence of CVD and no traditional CVD risk factors including dyslipidemia, HTN, obesity, or diabetes. None of the subjects were taking BP-meds, cholesterol-meds, or diabetes medications. Average age of subjects was 58.1y and the mean follow up was 14.5 years. They looked at subjects with SBP<100, 100-109, 110-119, and 120-129mmHg levels. Dr. Welton and associates found a stepwise increase in both coronary artery calcium (CAC) and ASCVD events with increasing SBP in what has long been considered the “normal” range below SBP <130mmHg. The authors concluded:

"In this study, there appeared to be a stepwise increase in traditional ASCVD risk factors, prevalence of coronary artery calcium, and risk of incident ASCVD with increasing SBP levels among individuals without hypertension or other traditional ASCVD risk factors. We demonstrated that this apparently positive graded association of SBP with coronary artery calcium and ASCVD begins at an SBP level as low as 90 mm Hg and that there did not appear to be a higher ASCVD risk at this low SBP level. Our results appear to support the importance of primordial prevention for SBP level increases along with other traditional ASCVD risk factors, all of which generally display similar trajectories of graded increase in risk within values traditionally considered to be normal" (5).

However, in this reviewer’s clinical experience with the Pritikin Eating Plan it is effective at reducing SBP even in those with what has been considered “normal” BP. Optimal sodium intake is likely between 500 to 1000mg per day for nearly everyone. The adverse effects of elevated BP and SBP includes not only CVD events but damage to the kidneys, brain, heart, arteries, and likely other organs and tissues. Indeed, elevated BP now appears to be associated with a significantly greater risk of serious disease and death in people infected with the new Wuhan coronavirus. While reducing dietary sodium to the optimal level of 500 to 1000mg per day is a safe and effective to lower BP and SBP in nearly everyone those who are currently taking BP-medications should consult with their MD about reducing their BP-medications as a sudden drop in salt intake may cause their BP to drop too low and/or contribute to an elevated risk of hyponatremia. 

Bottom Line: The results of this new study by Dr. Welton and associates seriously undermines the long-held assumption of what a physiologically normal BP level is. It shows the risk of ASCVD and developing CAC is about 4X greater for those with SBP in the 120s compared to 90s. Therefore, the optimal BP for humans is likely much lower than what many MDs claim is perfectly “normal”. However, the adverse effects of BP-medications may well be too great in most people to justify their use in those with only modestly elevated SBP levels. The only way for most people can maintain close to this new optimal SBP into old age appears to be to adopt a DASH-style diet with a sodium level below 1200mg/day with little or no alcohol. 

By James J. Kenney, PhD, FACN

References:

  1. http://foodandhealth.com/cpecourses/SaltCPE.doc Salt Toxicity, James J Kenney, PhD, FACN, Food and Health Communications Research Library
  2. MacGregor GA Hypertension. Jul-Aug 1985;7(4):628-40. doi: 10.1161/01.hyp.7.4.628
  3. Vasan RS, et. al. Impact of high normal blood pressure on the risk of cardiovascular disease. N Engl J Med. 2001 Nov 1;345(18):1291-7. doi:10.1056/NEJMoa003417
  4. Sacks FM, et. al. Effects on Blood Pressure of Reduced Dietary Sodium and the Dietary Approaches to Stop Hypertension (DASH) Diet. https://www.nejm.org/doi/pdf/10.1056/NEJM200101043440101
  5. Association of Normal Systolic Blood Pressure Level With Cardiovascular Disease in the Absence of Risk Factors, Seamus P. Whelton, MD, MPH1; John W. McEvoy, MB, BCh, MHS1,2; Leslee Shaw, PhD3; et al Bruce M. Psaty, MD, PhD4,5; Joao A. C. Lima, MD, MBA6; Matthew Budoff, MD7; Khurram Nasir, MD, MPH1,8; Moyses Szklo, MD9; Roger S. Blumenthal, MD1; Michael J. Blaha, MD, MPH1, JAMA Cardiol. Published online June 10, 2020. doi:10.1001/jamacardio.2020.1731
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