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The Salt–Blood Pressure Connection

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A deeper look into the relationship between salt and hypertension

By James DiNicolantonio, PharmD, author of The Salt Fix

We’ve all been told over and over again that salt raises blood pressure, which in turn increases risk of strokes and heart attacks.

The theory, at first, made a lot of sense: excess quantities of salt cause the body to retain excess water and lead to high blood pressure in most people; consequently, reducing your salt intake will lower your blood pressure. Straight ahead, simple, logical — right?

It was dead wrong.

Here’s the truth: normal blood pressure is less than 120/80 mmHg. But reducing your salt intake to around 2,300 milligrams per day (1 teaspoon of salt) may only lower your blood pressure by a meager 0.8/0.2 mmHg. So, after enduring staggeringly bland and often debilitating salt restriction, your blood pressure may now hover around 119/80 mmHg — a mere blip, not a significant difference.

Plus, approximately 80 percent of people with normal blood pressure are not even sensitive to these meager blood-pressure-raising effects of salt; among those with prehypertension (a precursor to high blood pressure), roughly 75 percent are not sensitive to salt, and among those with full-blown hypertension, about 55 percent are immune to salt’s effects on blood pressure. Indeed, even in those with hypertension (blood pressure of 140/90 mmHg or higher), reducing salt intake may only lead to a reduction in blood pressure of just 3.6/1.6 mmHg.

As we’ve also seen, many people with normal blood pressure, pre­hypertension, and hypertension may even get a rise in their blood pressure if they restrict their salt intake. This is because when salt intake is severely limited, the body begins to activate rescue systems that avidly try to retain more salt and water from the diet. These rescue operations include the renin-angiotensin aldosterone system (well known for increasing blood pressure) and the sympathetic nervous system (well known for increasing heart rate). Clearly, this is the opposite of what you want to happen!

Another consequence of the low-salt diet is that your arteries can become more constricted (an increase in what’s called “total peripheral resistance”), due to the depletion of blood volume. To fight against this increased resistance in the smaller arteries, the heart needs to pump harder, and the pressure of the blood coming out of the heart would need to be even higher. Total peripheral resistance places additional stress on the heart and arteries, leaving you more vulnerable to chronically elevated blood pressure. In other words, low-salt diets may actually cause the very disease they are supposedly being used to prevent and treat, hypertension. 

 

Published June 28, 2017.

 

The Salt Fix Book CoverReprinted from The Salt Fix: Why the Experts Got It All Wrong — and How Eating More Might Save Your Life. Copyright © 2017 by Dr. James DiNicolantonio. Published by Harmony Books, an imprint of the Crown Publishing Group, a division of Penguin Random House LLC.

 

James DiNicolantonio, PharmD, is a cardiovascular research scientist and doctor of pharmacy at Saint Luke's Mid America Heart Institute in Kansas City, Missouri. A well-respected and internationally known scientist and expert on health and nutrition, he has contributed extensively to health policy and medical literature and serves as the associate editor of BMJ Open Heart, a journal published in partnership with the British Cardiovascular Society. Follow him on Twitter @drjamesdinic.

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