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 The study did not measure dietary sodium directly, instead using
urine samples to estimate levels of sodium consumed, but the results
align with other large studies of sodium intake and blood pressure
risk, researchers say.
“A small amount of salt (less than 3,000 milligrams a day) is
necessary for us, but excessive salt is dangerous,” said coauthor
Dr. Tomonori Sugiura of Nagoya City University Graduate School of
Medical Sciences in Japan.
To excrete excess amounts of sodium, the body has to increase blood
pressure, Sugiura told Reuters Health by email.
Dietary sodium levels are much higher in Japan than in the U.S., but
most people eat too much in both countries, Sugiura said.
U.S. government dietary guidelines recommend consuming no more than
2,300 mg of sodium a day, equivalent to about two-thirds of a
teaspoon of salt, and that people with existing high blood pressure
or risk factors for it limit total sodium to 1500 mg daily. Past
research indicates the average American consumes about 3,600 mg of
sodium a day.
Scientists are still debating whether high levels of sodium intake
among people with normal blood pressure could cause chronic high
blood pressure or other cardiovascular problems to develop (see
Reuters articles of November 9, 2011 and February 14, 2013 here:
http://reut.rs/1IKSJgH and http://reut.rs/1g7ZMxi).
But if it does contribute, sodium intake would be a risk factor that
would be easy to modify to benefit public health, the authors write
in the Journal of the American Heart Association (AHA).
The researchers used urine tests from checkup appointments to
estimate the dietary salt intake of 4,523 Japanese adults without
high blood pressure. The participants, who ranged in age from 22 to
85 years old, had annual physicals including sodium tests and blood
pressure measurements.
The study team used these records to follow people for three or more
years to see if they developed high blood pressure. During the
study, 1,027 individuals developed high blood pressure, including 26
percent of the men and almost 17 percent of the women.
Having higher sodium levels at the beginning of the study and
showing greater increases in sodium levels each year were both tied
to higher risk of developing high blood pressure, the researchers
found.
At the start of the study, the participants were consuming an
average of 4,200 milligrams of dietary sodium per day. Those who
would go on to have high blood pressure were eating an average of
4,500 milligrams per day.
Men tended to have higher urinary sodium levels than women. And
people who developed high blood pressure also tended to be heavier
and older.
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“Salt is one of the most important factors in the prediction of
hypertension,” Sugiura said. “Other important lifestyle factors
include obesity and too much alcohol intake.”
People with diabetes, obesity, a history of cardiovascular disease,
and those with systolic blood pressure greater than130 millimeters
of Mercury (mmHg) or diastolic blood pressure greater than 85mmHg
should pay the most attention to their sodium intake, Sugiura said.
Trials that actually test changes in diet, as opposed to observing a
population as this study did, have shown that modest reductions in
sodium intake will decrease the instance of high blood pressure,
according to Dr. Paul K. Whelton of Tulane University School of
Public Health and Tropical Medicine in New Orleans.
“For people with established (high blood pressure), reducing sodium
intake reduces the need for hypertension therapy,” Whelton, who was
not part of the new study, told Reuters Health.
Exact sodium guidelines vary by country and advisory source, but in
a way they are irrelevant because “no one is even close to it,” he
said. More than 90 percent of U.S. adults exceed recommendations, he
said.
While individuals can try to limit their sodium intake on a daily
basis, the vast majority of sodium in our diets comes from processed
food, so gradually reducing the amounts in those foods would have
important health benefits without asking people to actually change
their behavior, Whelton said.
“Adding sodium at the table not very important, about 80 percent of
what we get is added during processing,” he said.
So far, manufacturers have not been pressured to reduce sodium
levels, due to powerful commercial lobbies, he said. Salty processed
foods make consumers thirsty, and many of the same manufacturers
also make sodas, he noted.
Whelton has found in his own studies that “the more you can reduce
your sodium intake the better off you were, even those with a small
reduction.”
SOURCE: http://bit.ly/1I897lR Journal of the American Heart
Association, online July 29, 2015.
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