Some studies actually suggest that in subgroup populations, it may be potential harm by increasing rate of heart attack and death. As sodium levels drop, triglyceride levels increase, insulin resistance increases and the sympathetic nervous system activity increases. Each of these factors increase risk of heart disease, so perhaps lowering sodium intake has effects on more than just blood pressure.
The articles suggest that the inconsistency between the various studies are hard to account for because there are a lot of factors to consider (e.g. amount of exercise each study subject gets, relying on people's recall on how much salt they consumed, variations in how each study defined what was considered "high" or "low" sodium diets). Moreover, most of these studies were before 2005, and although more recent studies are more careful and rigorous, adverse events were found in the lower end of salt intake.
Many of the food on shelves of supermarkets today contain large amounts of sodium, especially in the processed foods. This makes it almost impossible for most Americans to cut back on sodium intake. Also, foods generally just taste bland without salt. Even if one does succeed in maintaining a low sodium diet, the effects on decreasing blood pressure are very minimal, at best (roughly 1 mmHg for both systolic and diastolic blood pressure).
Our kidneys are designed, by nature, to balance the amount of sodium and other electrolytes in our bodies. So the take home message is to have a consistent diet and generally not have too much or too little of anything in the diet, whether its salt, sugar, protein, etc.
Posted by: Adrian Lee; PharmD Candidate 2014