The argument over how much salt in the diet is too much has been going on for decades. One camp says that we all need to eat less salt. The other scoffs at this tasteless idea, claiming that cutting back on salt would have little effect on public health. One thing missing from the sometimes heated debate is evidence about the long-term effects of lowering salt intake. Until now, there has been little information on what really matters: salt's effect on heart disease and survival.
That's changing, thanks to persistent work from a national team headed by researchers at Harvard-affiliated Brigham and Women's Hospital. Their work suggests that modestly reducing salt intake can pay off in terms of fewer heart attacks, strokes, and premature deaths from cardiovascular disease. Whether this works for everyone, or just for people with blood pressures above the healthy range, remains to be determined.
Your daily target for salt should be guided by your health.
Taking the long view
To get a handle on the long-term effects of cutting back on salt, epidemiologist Nancy R. Cook and her colleagues turned to the Trials of Hypertension Prevention (TOHP), two trials they had conducted in the late 1980s and early 1990s. The first TOHP looked at four strategies for lowering blood pressure: weight loss, stress management, nutritional supplements, and salt reduction. The second one tested only weight loss and salt reduction.
The two trials didn't make a huge splash, mostly because the intense dietary and behavioral counseling that was provided to the participants yielded fairly small reductions in blood pressure. The TOHP results were overshadowed a few years later by more compelling findings from the Dietary Approaches to Stop Hypertension (DASH) trial. It yielded bigger drops in blood pressure from a diet rich in fruits, vegetables, low-fat dairy foods, whole grains, beans, nuts, fish, and poultry. A lower-sodium DASH diet proved to be even better.
Fast-forward 10 years. Dr. Cook and her colleagues gathered health information on all the sodium or sodium-control TOHP participants they could track down — just over three-quarters of the volunteers. Among those who had been in the control groups, 9% had suffered a heart attack or stroke or died of cardiovascular disease in the years after the trial, compared with 7.5% from the sodium reduction groups. That doesn't seem like much of a difference. But when you consider that more than 1.5 million Americans have heart attacks or strokes a year, this small difference could mean preventing thousands of these catastrophes annually.
Table salt isn't entirely a demon. Your body needs some sodium to transmit nerve impulses, contract and relax muscle fibers (including those in the heart and blood vessels), and maintain a proper fluid balance. But it doesn't take much to meet the body's needs.
In some people, the kidneys effortlessly flush excess sodium into the urine. In others, the kidneys can't keep up. Sodium accumulates in the fluid between cells. Water follows sodium, leading to an increase in the amount of water in the body and the volume of blood in circulation. Blood pressure climbs, and the heart must work harder.
The TOHP trials weren't about sodium restriction — cutting out as much salt as possible. Instead, they focused on sodium reduction. The volunteers ate their normal diets but learned how to look out for hidden salt and avoid it.
That's an important strategy. You can't always taste hidden salt; a one-cup serving of Cheerios has more salt than a one-ounce serving of salted potato chips.
If you want to cut back on salt, here are three tips:
- Check out the fine print. Choose foods low in sodium by reading food labels.
- Make it at home. Limit the use of canned, processed, and frozen foods.
- Don't hesitate to ask. When eating out, ask if items are prepared with salt; in fast-food restaurants, ask for a nutrition information sheet.
November 2007 update