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Salt! Bad for Slugs and Humans
Abstract & Commentary
By Allan J. Wilke, MD, Residency Program Director, Associate Professor of Family Medicine, University of Alabama at Birmingham School of Medicine—Huntsville Regional Medical Campus, Huntsville. Dr. Wilke reports no financial relationship to this field of study.
Synopsis: Limiting dietary sodium can reduce blood pressure and morbidity and mortality from cardiovascular disease.
Source: Cook NR, et al. BMJ. 2007;334:885-892.
The trials of hypertension prevention phase I (TOPH I) and phase II (TOPH II) were conducted in the late 1980s and early 1990s, respectively. These studies investigated several hypertension treatments including weight loss, sodium restriction, stress management, and dietary supplements, such as minerals and fish oil. The two studies randomized a total of 3126 patients to a sodium intervention or control group. The enrollees in these studies had similarities, but also some differences. At the initiation of the studies, patients were 30-54 years old (average around 43), about two-thirds male, mainly white, and not on antihypertensive medications. Patients in TOPH I had mean diastolic blood pressures (DBP) of 84 mm Hg; in TOPH II, DBP averaged 86 mm Hg. Mean systolic blood pressure (SBP) in TOPH I was 125; in TOPH II it was 127. The average body mass index (BMI) in TOPH I was 27.1. TOPH II purposefully enrolled patients with weights 110-165% of desirable and the average BMI was 30.9. Both studies demonstrated modest reductions in blood pressure (SBP/DBP 1.7/0.8 in TOPH I and 1.2/0.7 in TOPH II) and urinary sodium excretion in the intervention groups.
From 2000 to 2005, the investigators followed the patients, collecting data on cardiovascular events (myocardial infarction, stroke, coronary artery bypass graft, coronary angioplasty, and cardiovascular death) and self-reported sodium intake. The follow-up rate was 77%. The overall rate of cardiovascular disease (CVD) in the restricted sodium groups was 7.5%, compared to 9.0% in the control groups. Overall mortality was 2.3% and 2.6%, respectively. The results were not affected when the data were analyzed by age, gender, race, BMI, and active weight loss intervention. Additionally, individuals in the intervention groups reported a dislike for salty food more often than those in the control groups (48% vs 32%), used low-sodium products more frequently (47% vs 29%), and read food labels for sodium more frequently (66% vs 44%).
"Hello, I'm Allan, and I'm a saltaholic." In fact, I'm eating cheese and crackers and dry-roasted peanuts as I write this. I'm not alone. According to the National High Blood Pressure Education Program, the average daily sodium intake in the US in 1999 was 4,000 mg; the recommended intake is 2,400 mg.1 The good news is that, at least according to this study, I have a half-way decent chance of training myself to eat less salt-laden foods.
These individuals had prehypertension (120-139/80-89), which affects 45 million Americans.2 Is a reduction in CVD from 9.0% to 7.5% and mortality from 2.6% to 2.3% over 10-15 years clinically significant? Traditional analysis would say that this translates into a number-needed-to-treat (NNT) of 67 for CVD and 333 for mortality. These are not the numbers that will likely change a patient's behavior, but when we are wearing our public health hats, it should change ours. For one thing, we should be pushing for more efforts to reduce the sodium content of processed food.
A Cochrane review3 in 2004 concluded, "Intensive interventions, unsuited to primary care or population prevention programmes [my emphasis], provide only minimal reductions in blood pressure during long-term trials. Further evaluations to assess effects on morbidity and mortality outcomes are needed for populations as a whole and for patients with elevated blood pressure." TOPH I and II were included in this review.
When my residents ask about using the newest medication for disease X that they heard about from the pharmaceutical representative of company Y, I invariably will ask them (the residents and the drug reps) if there is any data on morbidity or mortality. The same standard must be applied to nonpharmaceutical interventions. For cardiovascular disease, it is not enough that blood pressure is lowered or cholesterol is reduced. Although I have recommended to them (the residents) that they advocate for salt restriction to reduce blood pressure, I haven't had much evidence to offer that it would do any good. Now I do.
1. http://www.nhlbi.nih.gov/health/prof/heart/hbp/salt_upd.pdf (accessed June 11, 2007).
2. Fields LE, et al. Hypertension. 2004;44:398-404.
3. Hooper L, et al. Cochrane Database Syst Rev. 2004;(1):CD003656. Review.