We’ve all had it drilled into us that too much salt is bad. And it is – it causes high blood pressure and according to http://www.actiononsalt.org.uk/less/Health/ it is linked to stomach cancer, osteoporosis, kidney stones, kidney disease, and vascular dementia. But how much is too much? It seems several organizations want us to reduce our salt intake drastically, but research shows that consuming too little salt is just as bad as consuming too much.
Action Salt says we need slight less than 1 gram a day and that the recommendation in Britain is a maximum of 6 grams a day. But Aaron Carroll did a piece (1) for the New York Times last year, referencing a study that found 3-6 grams was a safe amount to consume, and over 7 grams a day could increase mortality. And this article (2) in Scientific American from 2011 said pretty much the same thing. But public health officials seem to think less is better. The FDA recommends 2.3 grams a day, the WHO says 2 grams is the maximum and the American Heart Association recommends only 1.5 grams.
However, it appears that too little salt is just as bad for you as too much. A study (3) done last year showed that a sodium intake of between 3-6 grams a day was associated with a lower risk of cardiac death than a lower sodium diet of less than 3 grams. In fact mortality and risk of cardiovascular event was higher in the LOW salt group. So why does the FDA, WHO, and AHA want us to eat less salt? People naturally think in extremes – if too much salt is bad, then eat as little as possible. It’s the same with vitamins – don’t just supplement, take a megadose! But extremes are often dangerous when it comes to nutrition.
What is the history of our fear of salt? More than 100 years ago, French doctors found that six of their patients with high blood pressure – known even then as a risk factor for heart disease – consumed a lot of salt. Scientists in the present day would argue that six patients is a really small sample size, but the idea caught on and eventually became dogma. In the 1970’s, Lewis Dahl claimed he had unequivocal proof that salt causes hypertension. He induced high blood pressure in rats by feeding them the equivalent of 500 grams of sodium a day. I think its pretty safe to say that anyone eating 83 times more than the upper limit of 6 grams a day would have hypertension. It’s an unrealistic amount and really proves nothing for the average person and studies like that are not helpful in determining public policy, but this is exactly what happened (4).
Dahl started working with rats in the 1960’s but had prior experience working with human populations and salt consumption in the previous decade. He and other researchers discovered that not all rats responded to a high salt diet by developing hypertension. They decided to breed rats for susceptibility or resistance to salt, accomplishing this task in three generations of breeding. The S rats responded with hypertension regardless of whether they ate a high salt diet or consumed a normal rat chow that contained just 1% salt. It just took longer to develop hypertension on the low salt diet (5). So if Dahl was feeding a high salt diet to his S rats, then of course they would develop hypertension. A better study would have been to feed normal rats a higher salt diet, but not outrageously high, to determine the relationship between salt and hypertension.
This information is not new, but it seems public policy can’t shake the idea that salt is bad. A 1999 symposium by the NIH concluded that sodium restriction is probably only beneficial for older adults, and that only the minority portion of the general population that is sensitive to salt would benefit from restriction. They concluded that a nutrient-rich diet could produce better results in blood pressure, most likely because such a diet would eliminate any mineral deficiencies (6). The DASH diet (7) has been shown to reduce blood pressure independent of sodium intake or calorie restriction (8) .
If you eat a healthy diet, you probably don’t need to worry about salt and can add a little here and there as needed. If you eat a lot of manufactured foods or fast food, then yes, you should take a look at your salt intake to make sure it doesn’t exceed 6 grams. But for those of us who eat a healthy diet and don’t have high blood pressure, salt is one less nutrient to worry about. I plan to continue adding a little freshly-ground sea salt to tomatoes and roasted veggies – it makes them taste so much better… and it makes me want to eat more of them!