Many people with high blood pressure see salt as a villain. According to conventional wisdom, just a few shakes can send blood pressure soaring. But is salt really so dangerous?
After decades of studies, scientists finally have an answer to that question: Yes -- and no. For many people, extra salt really does raise blood pressure. In a few cases, however, it seems to lower pressure. And for some people, it doesn't really matter one way or another.
If this seems confusing to you, you have lots of company. Scientists are puzzled, too. Nobody knows why some people are sensitive to salt and others aren't. But researchers do have some clear-cut advice: To be on the safe side, everyone should keep a lid on salt intake.
How much salt should I consume each day?
The average American consumes over 3,000 milligrams of sodium every day -- far more than the body actually needs. The Food and Nutrition Board recommends a daily intake of no more than 2,300 mg. And reducing salt to 1,500 mg a day may be even better.
A study published in the Annals of Internal Medicine in 2001 examined six diets and found that a low-sodium regimen could make a healthy diet even healthier. Half of the study subjects ate a typical American diet but were divided into three groups, each consuming different levels of sodium: high (3,300 mg each day), intermediate (2,400 mg per day), and low (1,500 mg each day.) The participants in the other half of the study ate meals rich in fruits and vegetables but low in fat and cholesterol (also known as the Dietary Approaches to Stop Hypertension or DASH diet.) Their diets also were subdivided into three different levels of salt consumption.
The one-sixth of the subjects who ate the lowest-sodium DASH diet enjoyed the greatest reduction in blood pressure, even among people who didn't have high blood pressure (also called hypertension) to start with. This group lost an average of 9 points from their systolic pressure (the top number in a blood pressure reading) -- the biggest drop in any group.
Among subjects who cut down on salt, hypertensive African American women over 45 achieved the largest reduction in blood pressure. By contrast, young white men without hypertension had relatively little response to a low-sodium diet, according to Myron Weinberger, MD, Director of the Hypertension Research Center at the Indiana University School of Medicine, who conducted the study.
Weinberger's findings highlight two important points: First, some people can significantly reduce their blood pressure by cutting back on salt. Second, salt is just a start. You can give your heart extra protection by getting plenty of fruits and vegetables every day and going easy on fats. Not only will you lower your blood pressure, you'll reduce your risk of atherosclerosis (a form of hardening of the arteries) and heart disease.
How common is salt sensitivity?
Some people are extra-sensitive to salt. When they cut back, their blood pressure goes down. When they overindulge, their pressure goes up. According to the Mayo Clinic, salt sensitivity is especially common among older people, African-Americans, and people with hypertension, kidney disease or diabetes. Overall, 26 percent of Americans with normal blood pressure and 58 percent of those with hypertension are salt sensitive, Weinberger estimates.
If I don't have high blood pressure, do I still need to watch my salt?
Another recent NHLBI study suggests that salt sensitivity can be a dangerous condition -- even among people who don't have high blood pressure. Researchers followed up on a group of 708 people who had been evaluated for salt sensitivity and hypertension 25 years ago and were surprised by their findings. Subjects who had normal blood pressure but were sensitive to salt were just as likely as subjects with hypertension to have died of heart disease.
In a press release from the NHLBI, Director Claude Lenfant says, "This study provides yet more evidence that Americans should be careful about their daily salt intake." Since there's no blood test or other quick way to measure salt sensitivity, it's best not to take any chances.
How can I cut back on salt?
You can start by going easy on the saltshaker. It's important to understand, however, that the average person gets 90 percent of his or her salt from other sources. Many "convenience" foods such as frozen dinners, restaurant meals, luncheon meats, fast foods, and canned soups are extremely high in salt. The best way to protect yourself is to prepare meals at home. If you do eat processed foods, check the labels carefully -- and aim for a daily dose of 2,300 mg of sodium or less from all your food sources.
-- Chris Woolston, M.S., is a health and medical writer with a master's degree in biology. He is a contributing editor at Consumer Health Interactive, and was the staff writer at Hippocrates, a magazine for physicians. He has also covered science issues for Time Inc. Health, WebMD, and the Chronicle of Higher Education. His reporting on occupational health earned him an award from the northern California Society of Professional Journalists.
Vollmer, W.M. et al. Effects off sodium intake on blood pressure: Subgroup analysis of the DASH-sodium trial. Annals of Internal Medicine. Dec. 18, 2001.135(12): 1019-1028.
National Heart Lung, and Blood Institute news release. Study shows new link between salt sensitivity and risk of death. Feb. 15, 2001.
McCarron, D.A. The dietary guideline for sodium: Should we shake it up? Yes! American Journal of Clinical Nutrition. May 2000. 71 (5): 1013-1019.
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals, Vitamins. http://darwin.nap.edu/books/0309085373/html/1319.html
Mayo Clinic. Sodium: Are you getting too much? July 2008. http://www.mayoclinic.com/health/sodium/NU00284
Reviewed by Peter Pompei, MD, a geriatrics specialist and associate professor of medicine at Stanford University School of Medicine.
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Last updated December 19, 2008
Copyright © 2002 Consumer Health Interactive