Transcript: The Evidence That Salt Raises Blood Pressure
Like any group with vested interests, the food industry resists regulation. Faced with a growing scientific consensus that salt increases blood pressure, major food manufacturers have adopted desperate measures to try to stop governments from recommending salt reduction. Rather than reformulate their products and save lives, manufacturers have lobbied governments, refused to cooperate, encouraged misinformation campaigns, and tried to discredit the evidence. After all, salt is the main source of flavor in processed foods. Of course, they could improve the flavor by adding real ingredients, but like making a pop-tart with actual strawberries, that would be more expensive and cut into profits.
The evidence that they’re trying to discredit includes double-blind randomized trials dating back decades. You take people with high blood pressure, put them on a sodium-restricted diet, and their blood pressure drops. Then, if you keep them on the low-salt diet and add a placebo, nothing happens. But if you instead give them salt in the form of a time-release sodium pill, their blood pressure goes back up. And, the more sodium you secretly give them, the higher their blood pressure climbs.
Even just a single meal can do it. If you take people with normal blood pressure and give them a bowl of soup containing the amount of salt a regular meal might contain, their blood pressure goes up over the next three hours compared to the same soup with no added salt. Why though? High blood pressure appears to be our body’s way to push the excess salt out of our system.
Dozens of such studies have been done, showing that if we reduce our salt intake, we reduce our blood pressure, and the greater the reduction, the greater the benefit. The so-called DASH diet, which I’ve covered before, is commonly used to capture the blood pressure benefits of a more plant-based population, but how do we know the benefits have anything to do with eating less salt instead of just from eating more fruits and vegetables? Because it was put to the test. Sure, eating healthier lowers blood pressure no matter how much salt we eat, but even if we stick to the same diet, lowering salt helps independently of other dietary improvements.
You can do this on a community level. You take two matched villages that both start out about the same. In the control village, on average, blood pressures went up or stayed the same. But in the village where they were able to cut down on salt intake, blood pressures went down, whereas if we don’t cut down, chronic high salt intake can lead to a gradual increase in blood pressure throughout life, as shown in the famous Intersalt study.
52 centers from 32 countries participated with hundreds of participants each, and four of those centers were in populations that ate so little salt they actually complied with the American Heart Association guidelines for salt reduction, something less than 1% of Americans achieve. In a population where everyone makes the cut off, not only was not a single case of high blood pressure found, but the older folks had the same blood pressure as the teenagers.
This is why including such populations is so important. If you just look at the 48 centers in the industrialized Western world, there does not appear to be any relationship between rising blood pressure with age and how much sodium people are getting every day. Just looks like a random assortment of dots. Now, the salt industry looks at this and says “Aha!—see I told you so, no relationship between salt and increasing blood pressures as you get older.” But maybe that’s because they’re all getting too much salt.
The American Heart Association recommendation is that everyone get their salt intake under here; so, they were all way over. You can imagine a similar result if this was instead lung cancer rates versus packs of cigarettes smoked every year. Whether you smoked 150 packs a year or 200 packs a year, it might not make much of a difference. To see a relationship between smoking and cancer, you’d have to compare smokers to those who rarely light up. And indeed, if you add in those low-salt populations that get little or no high blood pressure as they get older, you end up with a highly statistically significant relationship between increasing sodium and increasing blood pressure, but only if you include people that actually comply with the salt guidelines. As with so many lifestyle interventions, they only work if you actually do it.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
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