A high-salt diet not only contributes to hypertension, it can undermine the benefits of blood pressure medication, research shows.
A new study, which involved patients taking a fairly standard cocktail of three drugs for high blood pressure, found that the more salt they consumed, the less effective the medication became.
"What is striking about these results is the degree of the effect," said David Calhoun, a professor of medicine at the University of Alabama at Birmingham and co-author of the research, published in the medical journal Hypertension.
Patients with a high-salt diet - meaning they consumed about 2.5 teaspoons of salt daily - essentially negated the benefits of the medication, researchers found.
Conversely, those on a low-salt diet - about half a teaspoon daily - saw substantial drops in their blood pressure readings: 23 points in systolic blood pressure and nine points in diastolic blood pressure.
Blood pressure is a measure of the force of the blood against blood vessel walls. It is expressed in two numbers: Systolic, the upper number, is the pressure when the heart contracts; diastolic, the lower number, is the pressure when the heart is relaxed.
A person is considered hypertensive when a blood pressure reading is 140/90 millimetres of mercury (mmHg) or higher. In healthy adults, the reading should be in the range of 120/80 mmHg, although that target varies with age and health.
Beth Abramson, a cardiologist and spokeswoman for the Heart and Stroke Foundation, said there is an important message in this type of research: "Medications are never enough.You also need to watch your salt intake, control your weight, exercise - all those things make the medications work better."
They also help explain why many Canadians have trouble controlling their blood pressure.
Canadians are among the biggest consumers of salt in the world, and have some of the saltiest foods.
Canadians ingest, on average, 3,092 milligrams of sodium daily - about two teaspoons- according to Statistics Canada. Men consume markedly more sodium than women - 4,100 milligrams a day, compared with 2,900 milligrams.
The U.S. Institute of Medicine has established that the adequate daily intake for a healthy adult is between 1,200 and 1,500 milligrams of sodium - about three-quarters of a teaspoon - and it should be lower for people with cardiovascular conditions such as high blood pressure and heart failure, and for those who have had a heart attack or stroke.
Maria Ricupero, a dietitian in the cardiac program at Toronto Rehabilitation Institute, said it can be difficult for heart patients to reduce their consumption of salt because they tend to be set in their ways.
"My patients tend to be in their 50s and older, so they've been living with certain dietary habits for years. The learning curve can be steep."
Ms. Ricupero teaches patients to read labels and urges them to "work within a budget" of 1,500 milligrams a day of sodium when choosing their foods.
"You can spend your salt budget however you like. But if you splurge on a Big Mac it will run you 1,000 milligrams and you won't have much left, so you're better going with foods that have much lower concentrations," she said.
While Ms. Ricupero teaches individuals how to limit their salt consumption, she said greater efforts - regulatory and otherwise - should be made to get salt out of foods at the source.
After all, more than 80 per cent of salt consumption comes from processed foods. A study published last week by World Action on Salt and Health, an international health advocacy group, found that foods sold in Canada often contain more salt than seemingly identical products sold in other countries. This is true for products ranging from All-Bran cereal to Burger King Whoppers.
"Not having all this sodium in food in the first place would make my job a lot easier and it would make food a lot healthier," Ms. Ricupero said.
Jerry Tollinsky, a charity fundraiser in suburban Toronto, had a heart attack last November. He underwent heart surgery and then cardiac rehabilitation, working on making lifestyle changes that would prevent a recurrence.
A key component was learning how to reduce the amount of sodium in his diet by getting rid of the salt shaker, reading labels on packaged foods and cooking at home.
Mr. Tollinsky found out, to his horror, that 21/2 pickles contain as much salt as you should be eating in a day.
"What I learned is that sodium sneaks up on you. It's in everything," he said. "I love cold cuts. I love olives. I love pickles. I love hard cheese. But I don't eat those things much any more."
Mr. Tollinsky said that knowing a low-salt diet would make his heart medication more effective was a powerful incentive.
Cardiovascular disease is one of the leading killers of Canadians, claiming 65,628 lives in 2005, the most recent year for which mortality data are available from Statistics Canada. It is estimated that one in eight cardiac events are caused by excess sodium.
André Picard