Headlines were made, a month or two ago, by a mathematical-modeling study published in the New England Journal of Medicine suggesting that lowering average U.S. dietary salt intake by 3 grams - about a half-teaspoonful - per day would result in 44,0000 to 92,000 fewer deaths. Kindred putative benefits include substantially reduced heart-attack rates and coronary heart disease cases. (Stanford nephrologist Glenn Chertow, MD, MPH, contributed to that report.)
But this week, a commentary (registration may be required) in the Journal of the American Medical Association cautions against swift, sweeping public-health measures with the goal of dropping the country's collective salt intake. Written by Michael Alderman, MD, of the Department of Epicemiology and Population Health, Albert Einstein College of Medicine, the commentary makes some bracing observations:
Multiple randomized clinical trials... have established that reduction of sodium intake sufficient to lower blood pressure also increases sympathetic nerve activity, decreases insulin sensitivity, activates the renin angiotensin system, and stimulates aldosterone stimulation.
And who will watch over the guardians?
The only randomized clinical comparisons of different sodium intakes for which the endpoints were morbidity and mortality - the gold standard - have involved patients with heart failure, Alderman writes. And what happened?
[A] more restricted sodium intake significantly increased mortality and hospitalization. . . . These results are consistent with the view that overzealous restiction of sodium may be harmful for patients with heart failure.
Rarely, smoking accepted, do observational studies . . . justify a public health intervention. The 1980 National Dietary Guidelines recommended population-wide reduction of total fat intake. In response to an unanticipated epidemic of obesity and diabetes, to which the authors concluded the 1980 recommendations might have contributed, the 2000 committee withdrew its earlier recommendation. Trans-fat consumption and postmenopausal hormone therapy are other examples of how well-meaning interventions, based on insufficent science, can have hazardous consequences.
He's certainly right about that. In the January 13 issue of the American Journal of Clinical Nutrition, Ron Krauss, MD, of the Children's Hospital Oakland Research Institute, and colleagues published a big fat metastudy concluding that there was no link between saturated-fat intake and increased risk of coronary heart disease or cardiovascular disease. As founder of the American Heart Association's Council on Nutrition, Physical Activity, and Metabolism, Krauss knows a thing or two about cardiovascular disease risk. (He's done seminal work on the effect of low- versus high-carb diets on LDL particle size, a possibly important heart-disease risk factor.)
About 20 years ago consumer-health advocacy groups such as the Center for Science in the Public Interest began loudly pounding the drum about saturated fats then widely used by fast-food chains. The result was a public-relations-coerced conversion from lard and beef tallow to those delightful replacements known as partially hydrogenated vegetable oils - the source of the (now we know) truly evil trans-fats referenced in the paragraph above. That switch didn't work out so well.
Right-size those recommendations
Perhaps comparing salt reduction to saturated-fat cold turkey or to trans-fat substitution is unfair. Taking some of the salt out of the processed foods most Americans live on is probably pretty benign. After all, we can all still salt up to the max in the privacy of our kitchens if we so choose. On the other hand, effectively forcing people onto a trans-fat-rich diet by infusing their french fries with galloping globs of it - or miseducating them into what may, in retrospect, have turned out to be a rather ruinous high-carb diet by making them feel guilty every time they bite down on a cheeseburger - can be actively injurious.
That said, surely the ideal way to attack even the most widespread public-health problem is on a personalized basis. Those with low or middling salt intake should be left alone, and those with both high salt intake and evidence of, say, hypertension should certainly be encouraged to try cutting down to see if it makes a difference. But where food, genes and belt sizes mix, one size does not fit all.