Following a raft of large-scale studies showing that a high salt intake leads to high blood pressure, the Dietary Guidelines for Americans set the recommended sodium intake at 2,300 milligrams per day.
However, a new batch of studies are bringing this guideline into question, and researchers are now asking whether the relationship between hypertension and salt is so clear cut.
The latest research to probe sodium's role in hypertension is presented today at the Experimental Biology 2017 meeting, taking place in Chicago, IL.
Researcher Lynn L. Moore, an associate professor of medicine at Boston University School of Medicine in Massachusetts, completed the study with her team.
A new look at sodium and blood pressure
Moore and her team took data from 2,632 men and women aged between 30 and 64 years, who were part of the Framingham Offspring Study - an offshoot of the Framingham Heart Study. All participants had normal blood pressure at the start of the trial.
Over the 16-year follow-up period, the researchers observed that the participants who consumed under 2,500 milligrams of sodium each day had higher blood pressure than those who consumed higher quantities of sodium.
The results seem counterintuitive. As the authors write: "While we expected dietary sodium intake to be positively associated with both SBP [systolic blood pressure] and DBP [diastolic blood pressure], the opposite was found."
Although the findings appear to kick against the status quo, they are in line with other recent studies asking similar questions. Research has shown that there is a "J-shaped relationship" between cardiovascular risk and sodium. This means that low-sodium diets and very high-sodium diets both carry a higher risk of heart disease.
Many people in the United States sit in the middle of this curve, where the cardiovascular risk is at its lowest.
"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."
Lynn L. Moore
Potassium as important as sodium
The importance of dietary potassium is also underlined in this study. The team found that individuals with the lowest blood pressure were those who had the highest intake of sodium and potassium. Conversely, those with the highest blood pressure had the lowest intake of sodium and potassium.
Moore says: "This study and others point to the importance of higher potassium intakes, in particular, on blood pressure and probably cardiovascular outcomes as well."
The authors conclude that:
"These long-term data from the Framingham Study provide no support for lowering sodium intakes among healthy adults to below 2.3 grams per day as recommended. This study does support the finding of a clear inverse association between potassium, magnesium, and calcium and blood pressure change over time."
Moore wants her study to play a part in shifting dietary decisions throughout the U.S. She says: "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."
Moore also makes it clear that there may be certain people who are particularly sensitive to sodium and who might, therefore, benefit from reducing salt in their diet. Perhaps in the future, methods of screening for salt sensitivity might help to establish which individuals need to be more careful.
As more studies conclude that sodium's role in hypertension is less vital than once thought, dietary recommendations are sure to change in line with the findings. This changing field of nutrition science is one to watch.