It’s well-established that in overweight people, too much salt in the diet significantly raises the risk of heart attack and stroke. However, a study (O’Donnell et al) published by the Journal of the American Medical Association (JAMA), using urine tests of nearly 30,000 people, reports that too little salt, below 3.0 g per day, also significantly raises the risk of cardiovascular (CV) events, meaning heart attack, stroke, and hospitalization for congestive heart failure. Further, the study found that the risk of heart disease did not go up until salt intake went above 6.5 g per day, which is almost three times higher than the daily amount recommended by the American Heart Association (AHA), which is 2.3 g per day. Notice that the AHA recommended salt intake is below the lowest amount found to be safe in this study.
The study also notes that those with higher potassium levels ate more fruits and vegetables, and had a significantly lower risk of stroke.
Another JAMA study (Jiang et al) which followed 9,500 people for 19 years, found no association at all between normal weight people, salt intake and risk of CV events. There was a significantly increased risk of heart disease and death among overweight people whose salt intake was highest, but even then reported dietary salt intake didn’t go much above 3.5 g. The bottom line is that the more overweight a person is, the more sensitive they are to salt, and the more easily salt will raise blood pressure.
O’Donnell MJ, Yusuf S, Mente A et al, “Urinary sodium and potassium excretion and risk of cardiovascular events,” JAMA. 2011 Nov 23;306(20):2229-38.
He J, Ogden LG, Vupputuri S et al, “Dietary sodium intake and subsequent risk of cardiovascular disease in overweight adults,” JAMA. 1999 Dec 1;282(21):2027-34.