By Richard L. Hanneman
Summary: Gauging the effect sodium may have on our diets has been a bone of contention for many years. With extensive research, enough data exists to spread across both sides of the argument. Meanwhile, water treatment dealers are left to explain to customers what part sodium plays in the effectiveness of water softening equipment.
Consumers tell pollsters they’re confused about issues of diet and health. Small wonder. It seems every week there’s a new story that some nutrient or other causes some chronic disease or protects against it. Sounds good. Then the next week or month comes another headline claiming just the opposite. Sound familiar?
That’s the situation facing homeowners today seeking quality water for their families without risking their health. They read about “good nutrients” and “bad nutrients” and about “good foods” and “bad foods.” Some even prey on this fear; one “consumer” group generates its funding by scare-mailings warning of “ten foods you should never eat.”
Seeking the truth
Fighting an uphill battle for reason and sound science, dietitians teach there are no “bad nutrients” or “bad foods,” only “good diets” and “bad diets.” Even then, they feel the ground shifting beneath their feet. Science marches on. And science is a process of creative destruction. Today’s “truth” is bombarded with data and even long-held hypotheses often require revision.
Since the Republican took control of both houses of Congress in 1994, the federal government lavished record amounts of spending on bio-medical research. It only makes sense that these vastly-expanded research ventures produced—and may continue to produce—new understanding and insight that require us to unlearn cherished concepts of scientific truth.
One area undergoing such reassessment is the health consequences of dietary sodium. For more than a generation, every source of dietary sodium was suspect for increasing a person’s risk of having a “cardiovascular event”—a heart attack or a stroke. Such events are a major cause of “premature” death and cost Americans more than $300 billion every year in increased medical expenses and lost productivity. One risk factor for heart attacks and strokes is hypertension—elevated blood pressure. Reducing blood pressure can cut the risk of a heart attack or stroke, depending on how it’s done.
Since we’ve known for 4,000 years that salt or sodium plays an important role in determining blood pressure, and a large minority of the population is “salt sensitive”—meaning some people’s blood pressures will decrease modestly in response to significantly reduced dietary salt—dietary sodium has been labeled a “bad nutrient.” Water softener customers used to raise this issue frequently and some may still have questions.
These questions have new answers. In fact, even the questions are new. In treating high blood pressure, doctors use a variety of anti-hypertensive drugs as well as lifestyle-change strategies. The drugs were approved by the U.S. Food and Drug Administration and all work to lower blood pressure. Still, they may not all be effective in improving health due to side effects not carefully considered. Thus, the federal government is focusing more on what are termed “health outcomes.”
Later this year, the Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) will be reported, comparing health outcomes of four classes of anti-hypertensive drugs. Dr. Jeffrey R. Cutler of the National Heart, Lung and Blood Institute (NHLBI) has supervised the study and explains its importance: “Trials are based on the notion that different antihypertensive regimes, despite similar efficacy in lowering blood pressure, have other beneficial or harmful effects that modify their net effect on cardiovascular or all-cause morbidity and mortality.”
For years, the same situation applied to lifestyle interventions designed to improve blood pressure but untested regarding health outcomes. We knew that certain dietary and lifestyle interventions reduced blood pressure, at least in sensitive sub-populations. But, surprising as it is, scientists had never inquired about whether these interventions actually achieved their intended purpose of improving health. Does reducing dietary salt, for example, actually reduce a person’s chances of having a heart attack or a stroke?
Relatively new data
Although based on scientific insights dating from the early 1970s, the direct question of whether reducing dietary sodium actually works to improve health outcomes was only examined during the past decade. Those results are now coming in and should cause yet another shift in our understanding of scientific “truth.” Of the first eight “health outcome” studies of sodium reduction, not one study found those in the general population following low-sodium diets to have lowered their risk for cardiovascular events like stroke or heart attack.
The findings have vast public health implications—and will certainly make it easier to minimize water softener shoppers’ concerns about sodium in their drinking water.
Let’s look at the evidence to date. A review in Science, published by the American Association for the Advancement of Science, described the situation fairly: “After interviews with some 80 researchers, clinicians, and administrators around the world, it is safe to say that if ever there were a controversy over the interpretation of scientific data, this is it.” The author continued: “After decades of intensive research, the apparent benefits of avoiding salt have only diminished. This suggests either that the true benefit has now been revealed and is indeed small, or that it is non-existent and researchers believing they have detected such benefits have been deluded by the confounding of other variables.” This article won investigative reporter Gary Taubes the top prize from the National Association of Science Writers. He described scientists in revolt against data-deficient political correctness.
Dispensing the myth
Leading the scientific revolt has been Dr. Michael H. Alderman of New York City’s Albert Einstein School of Medicine. In 1995, shortly before assuming the presidency of the American Society of Hypertension, Alderman wrote in the American Heart Association journal, Hypertension, an analysis of the health outcomes related to diets of his hypertensive patients over an eight-year period. He found those in the lowest sodium-consuming quartile had more than four times as many heart attacks as those on normal sodium diets.
Alderman produced a second analysis of people with normal blood pressures. His second study also found risks higher—some 20 percent—among those on low-sodium diets.
Thus, the promised benefit of reducing dietary sodium—reducing the number of heart attacks—wasn’t confirmed and the Alderman work suggested the possibility that the reduced sodium triggers compensatory systems in the body (particularly activating the hormonal renin-angiotensen system) that produce stress and potentially greater risk of heart attacks.
NHLBI has also been investigating the health outcomes of various interventions to reduce cardiovascular events. Dr. Cutler produced his own health outcome analysis of the effect of reducing dietary sodium. He used the first six-years’ data from the government’s own Multiple Risk Factor Intervention Trial (MRFIT) database. MRFIT screened 361,662 men and chose 12,866 for a primary prevention trial aimed at testing the effect of multiple interventions on mortality from coronary heart disease over 44 months. Though a longtime advocate of universal sodium restriction, Cutler was forced to concede that he could document no health outcomes benefit, though he disputed the evidence suggested added risks.
Following up on the same database, Dr. Jerome D. Cohen of Saint Louis University analyzed 14 years of MRFIT data, examining the relationship between dietary sodium and mortality. He confirmed the pattern charted by Cutler, concluding that there is “no relationship observed between dietary sodium and mortality.”
Around the world
Researchers in other parts of the world also turned attention from blood pressure to health outcomes. In Scotland, the massive Scottish Heart Health Study did a follow-up study of its original study population to determine how many had survived 10 years later. The study found those on higher sodium diets had lower risks of a fatal heart attack.
In Finland, research on health outcomes related to dietary sodium reported at the 1998 American Heart Association Scientific Sessions by Dr. Veli-Pekka Valkonen concluded: “No association between urinary sodium excretion and risk of myocardial infarction was found in this study cohort.” Thus, Valkonen concluded: “…our results do not support the recommendations for entire populations to reduce dietary sodium intake to prevent coronary heart disease.”
Two studies were published that do claim a positive relationship between dietary sodium and cardiovascular outcomes, but only in overweight or obese men (not women, nor normal weight individuals). The data tell a different tale. A Johns Hopkins University team suggested that less sodium-dense diets reduce cardiovascular mortality in overweight Americans. The data show these overweight individuals actually consumed less sodium than the normal weight individuals, refuting the notion that increased mortality could be attributed to sodium. Likewise, the second study, earlier this year, reported that increases in sodium intake parallel increases in risk of cardiovascular events in obese men. Although the study adjusted for a number of important confounding factors, it didn’t adjust for any of the other key dietary electrolytes: potassium, calcium or magnesium. Thus, neither study that claim a positive result even for a subset of the population (overweight men) can be considered conclusive.
Clip out this article. When customers ask whether a home water softener raises health risks, ask whether they and their doctors are familiar with this latest research on “health outcomes.” Ask if they know that the Canadian Hypertension Society, Canadian Coalition for High Blood Pressure Prevention and Control, Health Canada Laboratory Centre for Disease Control and Heart and Stroke Foundation of Canada have come out against universal sodium restriction. Ask if they know the current position of the U.S. Preventive Services Task Force, which states:
“There is insufficient evidence that, for the general population, reducing dietary sodium intake or increasing dietary intake of iron, beta-carotene, or other antioxidants results in improved health outcomes.”
If we all begin asking the right questions, perhaps we’ll start getting the right answers.
- American Heart Association, May 3, 2001, website: http://www.americanheart.org/Support/Advocacy/advoc_042401_1.html.
- Huang Ti, “Medical Questions Regarding Dietary Salt,” The Salt Institute, website: http://www.saltinstitute.org/28.html.
- Cutler, J.R., “Which drug for treatment of hypertension?” Lancet, 353:604-5; 1999.
- Brunner, H.R., J.H. Laragh, et al., “Essential hypertension: Renin and aldosterone, heart attack and stroke,” New England Journal of Medicine, 286:441-449, 1972.
- Taubes, G., “The (political) science of salt,” Science, 281:898-907, 1998.
- Alderman, M.H., et al., “Low urinary sodium associated with greater risk of myocardial infarction among treated hypertensive men,” Hypertension, 25:1144-1152, 1995.
- Alderman M.H., et al., “Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I),” Lancet, 351:781-785, 1998.
- Neaton, J.D., R.H. Grim Jr. and J.A. Cutler, “Recruitment of Participants for Multiple Risk Factor Intervention Trial (MRFIT),” Controlled Clinical Trials, 8:41S-53S, 1987.
- Cutler, J.R., Presented at American Society of Hypertension annual meeting, San Francisco, Calif., May 30, 1997, (unpublished).
- Cohen, J.D., Presented at NHLBI Workshop on Sodium and Blood Pressure, Bethesda, Md., Jan. 28, 1999, (unpublished).
- Tunsall-Pedoe, W., “Comparison by prediction of 27 factors of coronary heart disease and health in men and women of the Scottish heart health study cohort study,” British Medical Journal, See Table 6, age-adjusted hazard ratios, 315:722-729, 1997.
- Valkonen, V.P., “Sodium and potassium excretion and the risk of acute myocardial infarction,” Presented at the American Heart Association Scientific Sessions, Dallas, Oct. 15, 1998, (unpublished).
- He, J., et al., “Dietary sodium intake and subsequent risk of cardiovascular disease in overweight adults,” Journal of the American Medical Association, 282:2027-2034, 1999.
- Tuomilehto, J., et al., “Urinary sodium excretion and cardiovascular mortality in Finland: a prospective study,” Lancet, 357:848-51, 2001.
- Fodor, J.G., et al., “Recommendations on dietary salt,” Canadian Medical Association Journal, 160: S29-S34, 1999.
- U.S. Preventive Services Task Force, U.S. Department of Health and Human Services, May 3, 2001, website: http://220.127.116.11/pubs/guidecps/text/CH56.txt.
About the author
Richard L. Hanneman is president of the Salt Institute, of Alexandria, Va. He can be reached at (703) 549-5648, (703) 548-2194 (fax), email: [email protected] or website: http://www.saltinstitute.org.