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Thursday, September 18, 2014

Sodium studies, with a grain of salt

Another week, another roiling debate about nutrition. In the immortal words of Iago the parrot, I’m going to have a heart attack and die from that surprise.

Actually, heart attacks are directly germane to this topic; strokes even more so. The particular goal of guidelines addressing salt (or sodium) intake is to prevent ambient high blood pressure, a major contributor to cardiovascular disease and the leading cause of stroke. There are numerous other health effects of sodium intake as well, including an influence on bone density, but blood pressure tends to grab the spotlight.

And spotlight it is at the moment. Recent studies have reached almost shockingly divergent conclusions about the pros and cons of sodium restriction. Compounding matters, the studies in question appeared in the very same issue of the New England Journal of Medicine, published on Aug. 14.

Two articles, by the same large, international group of researchers called the “PURE investigators,” standing for “Prospective Urban Rural Epidemiology“ study, challenged the current emphasis on restricting sodium. Or at least, that’s what the related headlines say. One of these studies looked at variation in sodium excretion in urine and its association with blood pressure; the other looked at the same measure and its association with all-cause mortality and cardiovascular disease.

For both of these studies, the authors used a database of morning urine specimens from over 100,000 people in 18 countries to estimate 24-hour sodium and potassium excretion, and from those estimated values, to extrapolate daily intake of sodium and potassium. We may leave the methods at that, other than noting that as estimates are predicated on estimates, the error bars get pretty wide, pretty fast.

As noted, the inevitably hyperbolic headlines attached to these studies suggest they found that we should abandon salt restriction, and pour it on. But here are what the authors concluded in their own words. In the first of the studies, they stated: “In this study, the association of estimated intake of sodium and potassium, as determined from measurements of excretion of these cations, with blood pressure was nonlinear and was most pronounced in persons consuming high-sodium diets, persons with hypertension, and older persons.”

If you think that’s a long way from “pour it on,” well, I agree. Essentially, the researchers found that excess sodium was most likely to raise blood pressure in older people, and those already prone to high blood pressure. And, high sodium intake was most important when sodium intake was ... high. Well, alrighty then.

Moving on. The second study concluded with this: “In this study in which sodium intake was estimated on the basis of measured urinary excretion, an estimated sodium intake between 3 grams per day and 6 grams per day was associated with a lower risk of death and cardiovascular events than was either a higher or lower estimated level of intake.”

Superficially, that translates to: we can eat too much salt, and we can eat too little. That we have long known, since sodium is an essential nutrient. Too little can result in a life-threatening condition called hyponatremia. The study may have raised questions about how much is too much, since the 3-gram threshold is higher than current recommendations, although not higher than prevailing intake. But we have to be careful not to over-interpret that isolated finding. What does it mean if your intake of sodium is lower than average for the population of which you are a member? It means you are different. That might be good, but it could readily be bad. Being “different” might mean not fitting in with prevailing norms for any number of reasons, from poor health to social isolation. A lower daily intake of salt could result merely from a lower daily intake of food. Where any of these factors is operative, they might account for variations in both blood pressure, and mortality, quite independently of sodium.

Wherever these first two studies left us, we couldn’t stay there long, because the third study followed immediately after to shake things up some more. This one, by a different group of investigators, obtained data about sodium intake and cardiovascular death for over 70 percent of the global population of adults. What’s good for the goose is good for the gander, so here is what these researchers concluded: “In this modeling study, 1.65 million deaths from cardiovascular causes that occurred in 2010 were attributed to sodium consumption above a reference level of 2.0 g per day.”

They went on to note that excess sodium intake was responsible for one in ten of all deaths from cardiovascular disease around the globe. Associated headlines either indicated that our salt intake is, indeed, too high; or more bluntly, that too much salt is killing us.

A pretty confusing batch of papers to say the least, and that, too, has made headlines.

Here’s where I think it all shakes out.

There is no doubt it’s possible to consume too little sodium, and there is no doubt it’s possible to consume too much.

Not everyone is equally sensitive to sodium excess, and in general, it matters more as we age, and to those of us prone to high blood pressure.

A lower intake of sodium than prevails in a given population might indicate other important differences in behavior, health, or social integration. The current studies account for these imperfectly.

The studies purportedly raising questions about the importance of sodium restriction are actually only challenging the optimal threshold, suggesting it should perhaps be 3 grams daily rather than the current World Health Organization recommendation of 2 grams daily.

Missing from all headlines is this important tidbit: More than twice as many adults have a sodium intake above 6 grams daily as have an intake below 3 grams daily; and nearly 7 times as many have an intake above 4 grams, as have an intake below 3 grams.

This, in my view, leads to key point one: it is theoretically possible to consume too little sodium, but whether the relevant cut-point is set high or low, the vast majority of adults living in the real world consume too much. All three studies actually agreed on this point.

So, yes, I presume if you fill a house with water, it might cause drowning. But I’m not sure that theoretical concern is of great practical value when putting out a fire.

The second key point, certainly for those of us in the U.S., is this: More than 75% of the sodium we consume comes from processed foods. This figures in the manipulation of recipes to maximize our calorie intake.

The implications are rather clear. Any shift from a diet of more to less processed foods will result inevitably in a decrease in sodium intake. That shift is advisable because of the decisive health benefits associated with it, and regardless of the specific contributions of sodium reduction to that benefit. A typical American diet tends to be too high in sodium whether the higher or lower cut-point is invoked. But its more important liability is likely the fact that it is a typical American diet, in which a third or more of calories routinely come from “junk.” There is no debate about the value of eating food in place of junk.

As ever, competing headlines propagating confusion are partly a result of the legitimate nuances associated with the incremental advance of scientific understanding, and partly the machinations of media profiting from hyperbole and intrigue. But we can bypass the potential confusion altogether if we take it all with the proverbial grain of salt.

Whether the topic du jour is sodium, or fructose; wheat or meat; gluten or saturated fat, we are subject to the impasse of perpetual confusion if we fixate sequentially on each successive study of each particular nutrient. If instead we embrace what we reliably know about healthful eating in general, sodium intake will tend to fall in the sweet spot, along with the intake of all other nutrients. In other words, we could reliably defend ourselves against hyperbole and headlines, malnutrition and misinformation alike, with wholesome foods, in sensible combinations.

Tune in next week when that news ... will be exactly the same.

David L. Katz, MD, FACP, MPH, FACPM, is an internationally renowned authority on nutrition, weight management, and the prevention of chronic disease, and an internationally recognized leader in integrative medicine and patient-centered care. He is a board certified specialist in both Internal Medicine, and Preventive Medicine/Public Health, and Associate Professor (adjunct) in Public Health Practice at the Yale University School of Medicine. He is the Director and founder (1998) of Yale University's Prevention Research Center; Director and founder of the Integrative Medicine Center at Griffin Hospital (2000) in Derby, Conn.; founder and president of the non-profit Turn the Tide Foundation; and formerly the Director of Medical Studies in Public Health at the Yale School of Medicine for eight years. This post originally appeared on his blog at The Huffington Post.

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Blog log

Members of the American College of Physicians contribute posts from their own sites to ACP Internistand ACP Hospitalist. Contributors include:

Albert Fuchs, MD
Albert Fuchs, MD, FACP, graduated from the University of California, Los Angeles School of Medicine, where he also did his internal medicine training. Certified by the American Board of Internal Medicine, Dr. Fuchs spent three years as a full-time faculty member at UCLA School of Medicine before opening his private practice in Beverly Hills in 2000.

And Thus, It Begins
Amanda Xi, ACP Medical Student Member, is a first-year medical student at the OUWB School of Medicine, charter class of 2015, in Rochester, Mich., from which she which chronicles her journey through medical training from day 1 of medical school.

Auscultation
Ira S. Nash, MD, FACP, is the senior vice president and executive director of the North Shore-LIJ Medical Group, and a professor of Cardiology and Population Health at Hofstra North Shore-LIJ School of Medicine. He is Board Certified in Internal Medicine and Cardiovascular Diseases and was in the private practice of cardiology before joining the full-time faculty of Massachusetts General Hospital.

Zackary Berger
Zackary Berger, MD, ACP Member, is a primary care doctor and general internist in the Division of General Internal Medicine at Johns Hopkins. His research interests include doctor-patient communication, bioethics, and systematic reviews.

Controversies in Hospital Infection Prevention
Run by three ACP Fellows, this blog ponders vexing issues in infection prevention and control, inside and outside the hospital. Daniel J Diekema, MD, FACP, practices infectious diseases, clinical microbiology, and hospital epidemiology in Iowa City, Iowa, splitting time between seeing patients with infectious diseases, diagnosing infections in the microbiology laboratory, and trying to prevent infections in the hospital. Michael B. Edmond, MD, FACP, is a hospital epidemiologist in Iowa City, IA, with a focus on understanding why infections occur in the hospital and ways to prevent these infections, and sees patients in the inpatient and outpatient settings. Eli N. Perencevich, MD, ACP Member, is an infectious disease physician and epidemiologist in Iowa City, Iowa, who studies methods to halt the spread of resistant bacteria in our hospitals (including novel ways to get everyone to wash their hands).

db's Medical Rants
Robert M. Centor, MD, FACP, contributes short essays contemplating medicine and the health care system.

Suneel Dhand, MD, ACP Member
Suneel Dhand, MD, ACP Member, is a practicing physician in Massachusetts. He has published numerous articles in clinical medicine, covering a wide range of specialty areas including; pulmonology, cardiology, endocrinology, hematology, and infectious disease. He has also authored chapters in the prestigious "5-Minute Clinical Consult" medical textbook. His other clinical interests include quality improvement, hospital safety, hospital utilization, and the use of technology in health care.

DrDialogue
Juliet K. Mavromatis, MD, FACP, provides a conversation about health topics for patients and health professionals.

Dr. Mintz' Blog
Matthew Mintz, MD, FACP, has practiced internal medicine for more than a decade and is an Associate Professor of Medicine at an academic medical center on the East Coast. His time is split between teaching medical students and residents, and caring for patients.

Everything Health
Toni Brayer, MD, FACP, blogs about the rapid changes in science, medicine, health and healing in the 21st century.

FutureDocs
Vineet Arora, MD, FACP, is Associate Program Director for the Internal Medicine Residency and Assistant Dean of Scholarship & Discovery at the Pritzker School of Medicine for the University of Chicago. Her education and research focus is on resident duty hours, patient handoffs, medical professionalism, and quality of hospital care. She is also an academic hospitalist.

Glass Hospital
John H. Schumann, MD, FACP, provides transparency on the workings of medical practice and the complexities of hospital care, illuminates the emotional and cognitive aspects of caregiving and decision-making from the perspective of an active primary care physician, and offers behind-the-scenes portraits of hospital sanctums and the people who inhabit them.

Gut Check
Ryan Madanick, MD, ACP Member, is a gastroenterologist at the University of North Carolina School of Medicine, and the Program Director for the GI & Hepatology Fellowship Program. He specializes in diseases of the esophagus, with a strong interest in the diagnosis and treatment of patients who have difficult-to-manage esophageal problems such as refractory GERD, heartburn, and chest pain.

I'm dok
Mike Aref, MD, PhD, FACP, is an academic hospitalist with an interest in basic and clinical science and education, with interests in noninvasive monitoring and diagnostic testing using novel bedside imaging modalities, diagnostic reasoning, medical informatics, new medical education modalities, pre-code/code management, palliative care, patient-physician communication, quality improvement, and quantitative biomedical imaging.

Informatics Professor
William Hersh, MD, FACP, Professor and Chair, Department of Medical Informatics & Clinical Epidemiology, Oregon Health & Science University, posts his thoughts on various topics related to biomedical and health informatics.

David Katz, MD
David L. Katz, MD, MPH, FACP, is an internationally renowned authority on nutrition, weight management, and the prevention of chronic disease, and an internationally recognized leader in integrative medicine and patient-centered care.

Just Oncology
Richard Just, MD, ACP Member, has 36 years in clinical practice of hematology and medical oncology. His blog is a joint publication with Gregg Masters, MPH.

KevinMD
Kevin Pho, MD, ACP Member, offers one of the Web's definitive sites for influential health commentary.

MD Whistleblower
Michael Kirsch, MD, FACP, addresses the joys and challenges of medical practice, including controversies in the doctor-patient relationship, medical ethics and measuring medical quality. When he's not writing, he's performing colonoscopies.

Medical Lessons
Elaine Schattner, MD, FACP, shares her ideas on education, ethics in medicine, health care news and culture. Her views on medicine are informed by her past experiences in caring for patients, as a researcher in cancer immunology, and as a patient who's had breast cancer.

Mired in MedEd
Alexander M. Djuricich, MD, FACP, is the Associate Dean for Continuing Medical Education (CME), and a Program Director in Medicine-Pediatrics at the Indiana University School of Medicine in Indianapolis, where he blogs about medical education.

More Musings
Rob Lamberts, MD, ACP Member, a med-peds and general practice internist, returns with "volume 2" of his personal musings about medicine, life, armadillos and Sasquatch at More Musings (of a Distractible Kind).

Prescriptions
David M. Sack, MD, FACP, practices general gastroenterology at a small community hospital in Connecticut. His blog is a series of musings on medicine, medical care, the health care system and medical ethics, in no particular order.

Reflections of a Grady Doctor
Kimberly Manning, MD, FACP, reflects on the personal side of being a doctor in a community hospital in Atlanta.

The Blog of Paul Sufka
Paul Sufka, MD, ACP Member, is a board certified rheumatologist in St. Paul, Minn. He was a chief resident in internal medicine with the University of Minnesota and then completed his fellowship training in rheumatology in June 2011 at the University of Minnesota Department of Rheumatology. His interests include the use of technology in medicine.

Technology in (Medical) Education
Neil Mehta, MBBS, MS, FACP, is interested in use of technology in education, social media and networking, practice management and evidence-based medicine tools, personal information and knowledge management.

Peter A. Lipson, MD
Peter A. Lipson, MD, ACP Member, is a practicing internist and teaching physician in Southeast Michigan. The blog, which has been around in various forms since 2007, offers musings on the intersection of science, medicine, and culture.

Why is American Health Care So Expensive?
Janice Boughton, MD, FACP, practiced internal medicine for 20 years before adopting a career in hospital and primary care medicine as a locum tenens physician. She lives in Idaho when not traveling.

World's Best Site
Daniel Ginsberg, MD, FACP, is an internal medicine physician who has avidly applied computers to medicine since 1986, when he first wrote medically oriented computer programs. He is in practice in Tacoma, Washington.

Other blogs of note:

American Journal of Medicine
Also known as the Green Journal, the American Journal of Medicine publishes original clinical articles of interest to physicians in internal medicine and its subspecialities, both in academia and community-based practice.

Clinical Correlations
A collaborative medical blog started by Neil Shapiro, MD, ACP Member, associate program director at New York University Medical Center's internal medicine residency program. Faculty, residents and students contribute case studies, mystery quizzes, news, commentary and more.

Interact MD
Michael Benjamin, MD, ACP member, doesn't accept industry money so he can create an independent, clinician-reviewed space on the Internet for physicians to report and comment on the medical news of the day.

PLoS Blog
The Public Library of Science's open access materials include a blog.

White Coat Rants
One of the most popular anonymous blogs written by an emergency room physician.

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