Sodium continues progress toward a pardon; potassium gains more blood-pressure prestige
High blood pressure — hypertension — affects more than one billion people worldwide.
The idea that dietary salt causes hypertension dates to the early years of the 20th century, and it was based on anecdotal evidence.
And, as the authors of one recent paper wrote, “The overall evidence in the first half of the 1900s suggests that a low-salt diet was not a reasonable strategy for treating hypertension.”
Nonetheless, we are told to limit our salt (sodium chloride) and other sodium intake to avoid high blood pressure and its harmful effects on heart health.
The 2015-2020 Dietary Guidelines for Americans advises healthy people to limit their sodium intake to 2,300mg a day (1 teaspoon of salt).
Those guidelines advise certain people to limit sodium intake to 1,500mg per day (2/3 teaspoon of salt):
- People over age 50
- People with hypertension or a family history
- People with diabetes or chronic kidney disease
- Victims of heart attacks or other cardiac problems
But the results of two new studies support prior signs that conventional advice on sodium is overly simplistic for most people, and quite possibly harmful.
Study #1: Current sodium guidelines may not lower blood pressure
The Framingham Offspring Study was led by researchers at the Boston University School of Medicine.
The Boston team followed the participants — 2,632 healthy men and women aged 30 to 64 years, with normal blood pressure — over a period of 16 years.
The volunteers recorded their diets over a six-day period, and took blood pressure tests periodically over the course of the study.
The researchers compared participants’ sodium intake with their blood pressure reading, and the results of that comparison contradict current recommendations on sodium intake.
As co-author Lynn L. Moore, DSc said, “We saw no evidence that a diet lower in sodium had any long-term beneficial effects on blood pressure. Our findings add to growing evidence that current recommendations for sodium intake may be misguided.”
In fact, the participants who consumed less than 2,500 milligrams of sodium a day had higher blood pressure than those who consumed more sodium.
This finding supports prior evidence showing that people with very high sodium intakes have higher risks of heart disease, while those with moderate (rather than low) sodium levels enjoy the greatest protection against hypertension.
"We saw no evidence that a diet lower in sodium had any long-term beneficial effects on blood pressure," said Moore. “Our findings add to growing evidence that current recommendations for sodium intake may be misguided."
Moore says it’s clear that an unknown proportion of people who’re sensitive to dietary salt would benefit from lowering sodium intake.
And she called for more research to learn how to screen for salt-sensitivity and to determine guidelines for intakes of sodium and potassium in that sub-population.
For more recent findings that question official sodium guidelines — and the difficulty of sticking to them — see Do Low-Salt Diets Hurt More than Help?, Salt Intake Set by the Brain, and Salt Exonerated (Mostly) by U.S. Experts.
Potassium, not sodium, may be the key
The Boston team also discovered that the participants with higher estimated levels of potassium, calcium, and magnesium had lower blood pressure over time.
“This study and others point to the importance of higher potassium intakes, in particular, on blood pressure and probably cardiovascular outcomes as well,” said Moore.
In fact, the participants with higher combined average daily intakes of sodium (3,717mg) and potassium (3,211mg per day) had the lowest blood pressure.
"This study and others point to the importance of higher potassium intakes, in particular, on blood pressure and probably cardiovascular outcomes as well," said Moore.
She went on to make a key point: “I hope that this research will help refocus the current Dietary Guidelines for Americans on the importance of increasing intakes of foods rich in potassium, calcium and magnesium for the purpose of maintaining a healthy blood pressure.”
For lists of the best food sources, see "Beyond bananas", and "Potassium and seafood", below.
Study #2: Evidence review points to potassium/sodium balance
The authors of a recent evidence review looked for links between blood pressure and sodium, blood pressure and potassium, and the effects of the ratio of those two minerals.
This review, led by University of Southern California professor Alicia McDonough, Ph.D., confirmed that many studies link higher potassium intakes to lower blood pressure, regardless of sodium intake.
Additionally, studies covered by the review that examined medical interventions for high blood pressure found that supplemental potassium lowered blood pressure.
In addition to the evidence review, McDonough looked at the university’s own animal lab data to see how potassium lowers blood pressure.
Those studies show that the body uses sodium to closely control potassium levels in the blood, which are critical to normal heart, nerve, and muscle function.
Balance between the two minerals is key.
When potassium levels are low, your body holds on to sodium to maintain the needed levels. Conversely, higher potassium levels help the body rid itself of excess sodium.
As Professor McDonough said, “Decreasing sodium intake is a well-established way to lower blood pressure, but evidence suggests that increasing dietary potassium may have an equally important effect on hypertension.”
However, it's very hard to cut back on sodium, as we reported in Salt Intake Set by the Brain.
McDonough says that if you eat a typical Western diet — which typically provides relatively high levels of sodium — you should raise your potassium intake.
Note: People with impaired kidney function may need to limit their daily potassium intake, and should consult a physician.
To reduce hypertension risk, it makes sense to boost your potassium intake.
Bananas are the best-known source of potassium, with about 420mg in each one, but there are many other sources, including many that have much more.
Here’s a list of the top 20 food sources of potassium, ranked from the most per serving (winter squash at 896mg) to the least (canned light tuna at 201mg):
- Beet greens
- Swiss Chard
- Winter squash
- Sweet potato
- White beans
- Yellowfin tuna
- Orange juice
- Chicken breast
- Canned tuna
Potassium in seafood
Most seafood is quite high in potassium in relation to other foods and to the US RDA (3,500 mg).
Milligrams per 100 gm/3.5 oz:
- Halibut – 576
- King Salmon – 505
- Sablefish – 459
- Silver Salmon – 455
- Sockeye Salmon – 375
- Scallops – 355
- Sardines – 341
- Mackerel – 314 mg
- Canned Sockeye – 288
- King Crab – 262
- Albacore Tuna – 237
- Shrimp/Prawns – 182
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- McDonough AA, Veiras LC, Guevara CA, Ralph DL. Cardiovascular benefits associated with higher dietary K(+) vs. lower dietary Na(+): evidence from population and mechanistic studies. Am J Physiol Endocrinol Metab. 2017 Apr 1;312(4): E348-E356. doi: 10.1152/ajpendo.00453.2016. Epub 2017 Feb 7. Review.
- Moore L, Singer M, Bradlee ML. Low Sodium Intakes are Not Associated with Lower Blood Pressure Levels among Framingham Offspring Study Adults. Presented at Experimental Biology. Apr 25, 2017.
- Wong MM, Arcand J, Leung AA, Thout SR, Campbell NR, Webster J. The science of salt: A regularly updated systematic review of salt and health outcomes (December 2015-March 2016). J Clin Hypertens (Greenwich). 2017 Mar;19(3):322-332. doi: 10.1111/jch.12970.