Junkfood Science: Traffic tickets for salt — Does healthy eating mean low-salt?

June 26, 2008

Traffic tickets for salt — Does healthy eating mean low-salt?

Salt makes food taste good. Therefore, it must be bad for us. Enjoying food means people might eat too much and get fat.

Believe it or not, that is the logic behind beliefs that everyone — from children to adults — should reduce their salt intake as an important part of ‘healthy’ eating.

Fears of salt have become so widespread, even little kids are being told it’s bad for them and given low-salt diets. Even a lot of adults believe that lowering their salt intake will prevent high blood pressure and heart disease. But salt is another food ingredient where the science and the voices of medical experts have had a hard time breaking through myths, fears and pop ideologies.

What may seem inconceivable, given the Red Lights being given to salt, is that there is no credible evidence low-salt diets can help prevent heart disease, high blood pressure or premature death. Nor is there any sound evidence to support fears that we’re eating too much salt and that high salt diets increase our risks for cardiovascular disease and deaths. Nor can we assume that putting everyone on low-salt diets “can’t hurt” and are benign. In fact, the medical research suggests the very opposite.

From the stack

From the stack of studies that didn’t receive much media attention, comes a recent detailed analysis of data from the National Health and Nutrition Examination Surveys (NHANES), trying to sort out the relationships between our sodium intakes and cardiovascular disease and all-cause mortality. As JFS readers know, the National Health and Nutrition Examination Surveys, under the Department of Health and Human Services, have gathered clinical information on representative samples of U.S. adults for decades. They provide what is viewed by healthcare professionals as the most accurate data on our diets, lifestyles and health. Since these are paid for by your tax dollars and the information is supposed to be used to help guide public health policies, you deserve to know the results.

This study, published in the Journal of General Internal Medicine, is the third in a series of examinations of NHANES data evaluating the effects of our sodium intakes on cardiovascular disease, blood pressure and deaths. It is also the most detailed to date by these investigators — none of whom have ever received financial reimbursements by any entity associated with salt. Researchers at the Department of Epidemiology and Population Health at Albert Einstein College of Medicine in New York, used the dietary assessments and detailed health exams from NHANES III (which ran from 1988 – 1994), representing 99 million non-institutionalized U.S. adults. They then followed these adults through the year 2000, using vital statistics on deaths and causes of death from the National Death Index.

To rule out possibilities that the results could reflect the affects of cancers or illnesses, the authors excluded those Americans who’d died within the first 6 months; those who’d had a previous heart attack, stroke or heart failure; and the outliers with extreme intakes of calories or salt. [If someone is eating fewer than 500 calories a day, something else is going on!] So, those put on low-salt diets for medical problems were excluded (16%) because their medical conditions could account for why they might be at greater risk for dying prematurely.

Average sodium intake among Americans was about 3,200 mg/day. To identify the effects of higher and lower intakes, the researchers divided salt intakes into quartiles. The raw data showed that those in the lowest quartile (average 1,500 mg/day) were more likely to be older, not smoke, be normal weight and have higher systolic blood pressures. The highest sodium quartile group (average sodium 5,500 mg/day) was more likely to be men, heavier, smoke and have higher diastolic blood pressures. Over about 9 years of follow-up, there were more deaths among those eating the lower amounts of salt.

Heart disease, high blood pressure and deaths were inversely related to salt intakes: the higher the sodium, the lower the risks; the lower the dietary salt, the higher the risks.

As with all observational studies, correlations cannot provide evidence of a cause, but the authors did their best to rule out potential factors that could account for these correlations.

So, to parse out the effects of dietary sodium intake itself, they factored for confounding influences, including: age, gender, race, education, added table salt, exercise, alcohol use, smoking, history of diabetes, history of cancer, systolic BP, cholesterol, dietary potassium, weight, treatment for hypertension, and calories. The associations between low-salt diets and higher rates of cardiovascular disease and all-cause mortality held.

The lowest sodium intakes — the 1500 mg/day amount some are saying we should all be eating — were associated with an 80% higher risk of cardiovascular disease compared with those consuming the highest salt diets. The lowest salt intakes were associated with a 24% higher risk of all-cause mortality. While these correlations aren’t tenable for these types of population studies, they clearly show that low-salt diets don’t reduce risks. The findings also show no increased risks associated with those among us eating the highest sodium diets.

Try as they might, these researchers were unable to show that among the general population, low-salt diets are associated with lower risks for developing cardiovascular disease or high blood pressure or premature death.

Try as they might, they were unable to show that the highest salt intakes among Americans are associated with higher risks for developing cardiovascular disease or high blood pressure or premature death. They even did a secondary analysis among just fat adults, adjusting for age, gender and calories, and still found no statistically significant correlations between salt intake and mortality.

Are our salt fears real?

Is there any support that we should worry that we or our children are currently eating too much salt? And is there any support for beliefs that the general population could benefit from public health recommendations to trim the salt in their diets in order to lower risks for developing cardiovascular disease, hyigh blood pressure or premature mortality?

This study’s findings are consistent with what has been seen among the other NHANES surveys of the American public. It’s also consistent with more than 17,000 studies published on salt and blood pressure since 1966, following populations for up to decades [reviewed here], none of which has shown that low-salt diets offer noticeable benefits. As Dr. David Klurfeld, Ph.D., professor and chairman of the Department of Nutrition and Food Science at Wayne State University, editor-in-chief of the Journal of the American College of Nutrition, said, “the better controlled studies fail to show a significant benefit on blood pressure for large groups with sodium restriction.” [Addendum: Low-salt diets have also been shown in randomized clinical trials to date, to offer no benefit in preventing high blood pressure during pregnancy (pre-eclampsia).] The evidence behind popular claims that salt is dangerous and that lowering salt is healthful, was examined here.

When we see a low-salt diet being prescribed as part of the treatment for an elderly Grandparent suffering from heart or kidney failure, it’s easy to think that if we eat low-salt it might prevent us ending up with those health problems. As logical as this simplistic notion might seem, it doesn’t work that way. Treatments can’t be confused with preventions. It would be like advocating chemotherapy for everyone to prevent cancers. Or, believing that if everyone ate less sugar it could prevent diabetes, since regulating blood sugars is part of diabetes management.

Cochrane recently released a systematic review of the clinical trial evidence on recommendations to reduce dietary salt for the prevention of cardiovascular disease. They examined randomized, controlled clinical trials studying low-salt diets, lasting at least 6 months and recording the short-term or long-term effects on cardiovascular disease, blood pressure and mortality. The eleven quality trials they identified had studied healthy people with normal blood pressures, people with high blood pressure and people being treated for high blood pressure.

Deaths didn’t differ between the low-salt intervention groups and the control groups. The same number of people died over time, whether they were on low-salt diets or not. After 1 to 5 years on low-salt diets, those who’d gotten advice to eat low-salt diets and intensive behavioral interventions, saw their systolic blood pressures reduced by a mere 1.1 mmHg, and diastolic blood pressures by 0.6 mmHg, even while successfully lowering salt intakes as confirmed by urinary 24-hour sodium excretions by 35.5 mmol.

Most of the public has no idea that the salt in our diets has such a nominal effect. As the reviewers wrote: “This reduction was not enough to expect an important health benefit.” Changes in blood pressures were also unrelated to the degree sodium had been reduced — in other words, more wasn’t better.

The Cochrane reviewers concluded that even “intensive interventions, unsuited to primary care or population prevention programmes, provide only minimal reductions in blood pressure during long-term trials.” For patients on antihypertensive medications, if future clinical trials can show that low-salt diets help reduce need for blood pressure medications without increasing cardiovascular events, they said, then "targeting low-salt diet interventions might be justified among patients with elevated blood pressure requiring drug treatment.” But there is no clinical evidence to support a benefit for the general public.

Remember that the Dietary Guidelines are about dietary advice for the general population, ages 2 years and up, not those suffering from certain medical conditions such as kidney disease and under the care of their doctor.

The flip side

If there’s no support that salt reduction improves health among the public, can such advice potentially harm people?

There’s a reason that the human species has always craved salt and gone out of its way to get it. But the idea that salt is actually good for us has become antithetical to today’s ideologies of healthy eating.

Our tastes for salt have an innate purpose, yet we rarely think about the benefits of salt or why we need it. As cardiologists have pointed out, our bodies are designed for salt and to compensate for excess intakes. When most of us eat a lot of salt, we just get thirsty and drink water, and our bodies excrete the excess sodium, while maintaining the balance of sodium in our blood and maintain our blood pressures. Having too much salt in our bodies, called hypernatremia, is extremely rare and occurs in about 1% of debilitated hospitalized patients as a symptom of an underlying disease or inability to drink water.

When we eat low salt diets, however, our sodium reserves are lower. So, if we get sick, exercise or go out in the hot sun and then drink water essential to avoiding dehydration, the amount of sodium in our body can more quickly become diluted to dangerously low levels.* That’s called hyponatremia. It’s the most common electrolyte disorder and a special risk for infants and elderly, according to Dr. Sandy Craig, M.D., at the Department of Emergency Medicine, University of North Carolina at Chapel Hill. It’s also dangerous and can result in swelling of our brain, seizures, coma, heat stroke, leg cramps, heart arrhythmias and circulatory collapse.

Not surprisingly, some of the longest-living people in the world also have the highest salt consumptions. Salt not only makes food taste better, it also improves the flavor of foods for those whose tastes or appetites are diminished, helping to prevent nutritional deficiencies especially among vulnerable populations, such as children and elderly. Salt has also had invaluable roles in food preparation and preservation, baking, culturing cheese, and making our food safer to eat since the earliest days of mankind. The healthful benefits of salts, discussed here, also include the importance of the very first functional food: iodized salt.

It’s also become popular to believe that we’re eating dramatically more salt over recent decades, because of all that processed food and all. The evidence doesn’t support this oft-repeated claim, as was covered in the salt shaker article.

There are growing numbers of studies in the medical literature suggesting low-salt diets might risk negative effects on our health in other ways, such as activating the rennin-angiotensin system and the sympathetic nervous system and increasing insulin resistance. These effects could actually raise risks for cardiovascular disease, according to the European Society of Cardiology Guidelines. In contrast, these experts reported randomized clinical trial evidence suggests that “an abundant sodium intake may improve glucose tolerance and insulin resistance, especially in diabetic, salt-sensitive, and or medicated essential hypertensive subjects.”

The importance of sodium to the survival of patients was dramatically shown in a study just published in the American Journal of Respiratory and Critical Care Medicine. Cardiologists followed 40 patients with pulmonary arterial hypertension (PAH), examining the role hyponatremia might play in their prognosis and right heart function. As they noted, hyponatremia is already known to be associated with decompensated heart failure and poor prognosis in patients with left ventricular systolic dysfunction. They found that those with hyponatremia were more likely to be hospitalized, have poorer right heart function, and a ten-fold higher risk of death than those with normal sodium levels. Hyponatremia remained a predictor of PAH outcomes after adjusting for World Health Organization class, diuretic use, right atrial pressure, and cardiac index. Among the patients in their study with hyponatremia, about 15% had survived two years, compared to 85% of those with normal sodium levels.

There are a lot of urban legends about salt, from “salt kills” to “cutting salt can add years to your life.” The scariest thing isn’t salt, though. It’s that scare-based legends and myths, rather than good science, are guiding public health policies, the “nutrition” education being given children, and the public health messages teaching everyone to fear salt. Agendas that are not about health.

© 2008 Sandy Szwarc

* Sam McManis at the Sacramento Bee just wrote an article trying to clear up some of the confusion and fears about hyponatremia and hydration for healthy people exercising and enjoying outdoor sports this summer. His helpful article is Knowledge for thirst.

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