Salt may be culprit for uncontrolled blood pressure
Reported July 21, 2009
NEW YORK (Reuters Health) – People with high blood pressure that isn’t controlled by multiple medications are likely eating too much salt, new findings in the journal Hypertension show.
Individuals with so-called resistant hypertension showed sharp reductions in their blood pressure when they dramatically cut their salt intake, Dr. Eduardo Pimenta of the University of Queensland School of Medicine in Brisbane, Australia and his colleagues found.
“It was an amazingly large reduction in blood pressure,” Dr. Lawrence J. Appel of Johns Hopkins University in Baltimore, who wrote an editorial accompanying the study, told Reuters Health. Appel estimated that 10% to 20% of people have resistant hypertension, meaning they are taking three or more blood pressure medications but their blood pressure is still too high.
But the reductions in sodium intake in Pimenta’s study-down to 1.15 grams per day-would be very tough for people to achieve in a real-world setting, Appel added. (Sodium levels in food are correlated with salt levels.) “You can advise people to reduce sodium but the food supply has so much sodium it’s very difficult for individuals to do this on their own.”
Pimenta and his team had 12 people with resistant hypertension alternate between low and high sodium diets for a week each, with a two-week “washout” period between the diets.
Study participants’ initial average systolic blood pressure, the top number in a blood pressure reading, was 145.8 millimeters of mercury (mm Hg), while diastolic pressure, the lower reading, was 83.9 mm Hg. They were taking an average of 3.4 antihypertensive medications each.
On the high sodium diet, they were consuming 5.7 grams of sodium daily, while the low-sodium diet contained 1.15 grams of sodium daily.
US and UK guidelines recommend people consume less than 6 grams of sodium daily, while the World Health Organization recommends reducing intake even further, to less than 5 grams. But people in the developed world typically consume 9 to 12 grams of sodium a day.
In the study by Pimenta and his team, going on the low-salt diet reduced people’s systolic blood pressure by 22.7 mm Hg, on average, and their diastolic pressure by 9.1 mm Hg.
“The current results suggest that patients with resistant hypertension are exquisitely salt-sensitive,” the researchers suggest. These individuals’ salt intake is probably causing them to retain so much fluid that standard…treatments for reducing blood pressure aren’t helping them, they add.
In the other study, Dr. Feng J. He of the University of London and her colleagues tested a less dramatic sodium reduction in 71 whites, 69 blacks, and 29 Asians. All spent two weeks on a low-sodium diet, and were then randomly assigned to take sodium pills or a placebo for six weeks, after which they were switched to the opposite treatment for another six weeks.
Being on placebo versus taking sodium was equivalent to consuming 6.5 grams per day of salt versus 9.7 grams daily.
In He’s study, participants’ blood pressure averaged 146/91 while they were taking the sodium tablets, but fell to 141/88 when they were on placebo. The differences were significant among whites, blacks, and Asians-which is important, He noted in an interview, because most studies to date have been done in whites, while blacks and Asians are at particularly high risk of complications from high blood pressure.
Cutting salt also led to changes in the urine that suggested the change might be producing additional benefits for the kidneys and heart and circulatory system beyond the effects on blood pressure, He and her team found. Study participants were also losing less calcium in their urine, so reducing salt could be helping to protect their bones, too.
The UK has been working with the food industry to gradually reduce the amount of sodium added to food, He noted. This is crucial, she pointed out, because 80% of the sodium intake for a typical person in the developed world comes from salt added to foods by industry. The beauty of the UK plan, she added, is that the consumer doesn’t have to do anything to reduce their salt intake. Since the effort began, the researcher noted, average salt intake in the UK has fallen from 9.5 to 8.6 grams daily. “You can see it’s already working,” she said.
The US is working on a similar effort, Appel noted, but “the UK is ahead of us right now.” In the meantime, he writes, instead of focusing on the next drug or the next device for controlling blood pressure, “a renewed and aggressive emphasis on lifestyle modification, specifically sodium reduction, is warranted in patients with resistant hypertension and uncontrolled blood pressure.”
People should pay particular attention to the sodium content of breads and cereals, Appel said. Even though individual products aren’t excessively high in sodium, he added, because people tend to eat a lot of these products, they can add up.
For the population at large, He said, the advice is clear: stop adding salt during cooking, stop adding salt at the table, and pay attention to food labels. Most important, according to He, is cooperation from the food industry in gradually lowering the amount of salt added to foods over time. “That would make it actually much easier for the general public.”
SOURCE: Hypertension, September 2009.