Long-Term Salty Diets Tied Again to High Blood Pressure
But eating sodium-rich foods over the short term doesn't have the same effect, study suggests
MONDAY, June 18, 2012 (HealthDay News) -- Indulging in a bag of chips or munching a handful of nuts now and then isn't likely to hurt you in the short run, but regularly chowing down on salty foods over several years may damage your blood vessels and lead to high blood pressure, a new study finds.
Researchers reporting in the June 18 online edition of Circulation said that eating too much salt over time may affect the lining of blood vessels, increasing the likelihood of developing high blood pressure.
"This study reinforces guidelines backed by the American Heart Association and other professional organizations that recommend reducing salt consumption to reduce your risk of developing high blood pressure," said Dr. John Forman, lead author of the study and assistant professor of medicine at Harvard Medical School in Boston.
High blood pressure, also called hypertension, can contribute to heart failure, stroke and kidney failure.
Researchers tracked the salt intake of 5,556 white men and women from the Netherlands over about six years. None of the participants had high blood pressure at the study's start.
By analyzing 24-hour urine samples collected periodically over several years, the researchers noted the amount of uric acid and albumin in the urine, markers of blood vessel damage. They also tracked the amount of salt, or sodium, the participants ate by measuring how much sodium ended up in their urine.
The researchers found that, over time, people who ingested more sodium had more uric acid and albumin in their urine.
The higher the levels of uric acid and albumin, the more likely those people were to develop high blood pressure if they continued on high-sodium diets, the investigators found. Over the approximately six-year period of the study, 878 new cases of hypertension (high blood pressure) were discovered.
Compared with the participants eating the least amount of sodium (about 2,200 milligrams a day), those eating the most (6,200 mg a day) were 21 percent more likely to develop high blood pressure. Those who had high uric acid and albumin levels and ate the most salt were 86 percent more likely to develop high blood pressure.
How much salt is 2,200 milligrams of salt? About a teaspoon.
Much of the sodium the average American consumes comes from processed foods. Forman cautions that people who don't use salt shakers at the table shouldn't assume they're not getting too much sodium. One cup of soup or a single-serving frozen dinner can have 1,000 milligrams of sodium.
The study showed an association between the markers of blood vessel damage and high blood pressure, but not a cause-and-effect relationship.
Dr. Gregg Fonarow, professor of cardiovascular medicine at the University of California, Los Angeles, said, "the research shows that in some individuals, there is an association between these markers -- uric acid and albumin -- and the subsequent diagnosis of hypertension."
Why salt causes blood vessel damage -- called "endothelial dysfunction" -- is not fully understood, said Fonarow. "Sodium exposure may lead to progressive changes in the lining of the blood vessels, eventually becoming irreversible," he said.
"And once you've developed hypertension, lowering your salt intake most likely won't be enough to normalize your blood pressure," he said.
The study also suggests that those with markers of blood vessel damage may be more negatively affected by a high-salt diet than others.
The idea that salt influences the development of high blood pressure is considered controversial by some experts. A study published last year in the Journal of the American Medical Association suggested that lower amounts of sodium in urine were associated with more cardiovascular disease deaths.
In order to link high salt intake more closely to blood vessel damage and subsequent high blood pressure, Forman said it would be necessary to follow many people over about 20 years, ideally using ultrasound to directly assess blood vessel health.
Fonarow said the key to high blood pressure prevention is moderation and watchful management of other cardiovascular risks. "Avoid a high-salt diet, but also don't smoke, watch your weight, keep your cholesterol down and manage your blood pressure," he said. "Those factors are probably even more important."
Heart experts advise limiting sodium intake to less than 2,300 mg a day, or 1,500 mg if you're black, over 50 years old or have certain chronic diseases. By reading Nutrition Facts labels closely, you can limit your sodium intake.
The U.S. National Library of Medicine has more about high blood pressure.