Sodium in humans
<p >In humans, sodium is an essential nutrient that regulates blood volume, blood pressure, osmotic equilibrium and <a href="http://en.wikipedia.org/wiki/PH" title="PH" >pH</a>; the minimum physiological requirement for sodium is 500 milligrams per day.<sup id="cite_ref-r31_46-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-r31-46" >[47]</a></sup> <a href="http://en.wikipedia.org/wiki/Sodium_chloride" title="Sodium chloride" >Sodium chloride</a> is the principal source of sodium in the diet, and is used as seasoning and preservative, such as for <a href="http://en.wikipedia.org/wiki/Pickling" title="Pickling" >pickling</a> and <a href="http://en.wikipedia.org/wiki/Jerky_(food)" title="Jerky (food)" class="mw-redirect" >jerky</a>; most of it comes from processed foods.<sup id="cite_ref-47" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-47" >[4</a></sup>
<sup id="cite_ref-47" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-47" >8]</a></sup> The <a href="http://en.wikipedia.org/wiki/Dietary_Reference_Intake" title="Dietary Reference Intake" >DRI</a> for sodium is 2.3 grams per day,<sup id="cite_ref-48" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-48" >[49]</a></sup> but on average people in the United States consume 3.4 grams per day,<sup id="cite_ref-49" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-49" >[50]</a></sup> the minimum amount that promotes <a href="http://en.wikipedia.org/wiki/Hypertension" title="Hypertension" >hypertension</a>;<sup id="cite_ref-50" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-50" >[51]</a></sup> this in turn causes 7.6 million premature deaths worldwide.<sup id="cite_ref-51" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-51" >[52]</a></sup></p>
<p>
The <a href="http://en.wikipedia.org/wiki/Renin-angiotensin_system" title="Renin-angiotensin system" class="mw-redirect" >renin-angiotensin system</a> regulates the amount of fluids and sodium in the body. Reduction of blood pressure and sodium concentration in the kidney result in the production of <a href="http://en.wikipedia.org/wiki/Renin" title="Renin" >renin</a>, which in turn produces <a href="http://en.wikipedia.org/wiki/Aldosterone" title="Aldosterone" >aldosterone</a> and <a href="http://en.wikipedia.org/wiki/Angiotensin" title="Angiotensin" >angiotensin</a>, retaining sodium in the urine. Because of the increase in sodium concentration, the production of renin decreases, and the sodium concentration returns to normal.<sup id="cite_ref-52" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-52" >[53]</a></sup> Sodium is also important in <a href="http://en.wikipedia.org/wiki/Neuron" title="Neuron" >neuron</a> function and osmoregulation between cells and the <a href="http://en.wikipedia.org/wiki/Extracellular_fluid" title="Extracellular fluid" >extracellular fluid</a>, their distribution mediated in all animals by <a href="http://en.wikipedia.org/wiki/Na%2B/K%2B-ATPase" title="Na+/K+-ATPase" >Na<sup >+</sup>/K<sup >+</sup>-ATPase</a>;<sup id="cite_ref-53" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-53" >[54]</a></sup> hence, sodium is the most
prominent cation in extracellular fluid.<sup id="cite_ref-54" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-54" >[55]</a></sup></p>
<p>
In <a href="http://en.wikipedia.org/wiki/C4_plants" title="C4 plants" class="mw-redirect" >C4 plants</a>, sodium is a <a href="http://en.wikipedia.org/wiki/Micronutrient" title="Micronutrient" >micronutrient</a> that aids in metabolism, specifically in regeneration of <a href="http://en.wikipedia.org/wiki/Phosphoenolpyruvic_acid" title="Phosphoenolpyruvic acid" >phosphoenolpyruvate</a> and synthesis of chlorophyll.<sup id="cite_ref-55" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-55" >[56]</a></sup> In others, it substitutes for<a href="http://en.wikipedia.org/wiki/Potassium" title="Potassium" >potassium</a> in several roles, such as maintaining <a href="http://en.wikipedia.org/wiki/Turgor_pressure" title="Turgor pressure" >turgor pressure</a> and aiding in the opening and closing of stomata.<sup id="cite_ref-56" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-56" >[57]</a></sup> </p>
<p>
Excess sodium in the soil limits the uptake of water due to decreased <a href="http://en.wikipedia.org/wiki/Water_potential" title="Water potential" >water potential</a>, which may result in wilting; similar concentrations in the <a href="http://en.wikipedia.org/wiki/Cytoplasm" title="Cytoplasm" >cytoplasm</a> can lead to enzyme inhibition, which in turn causes necrosis and chlorosis.<sup id="cite_ref-57" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-57" >[58]</a></sup> </p>
<p>
To avoid these problems, plants developed mechanisms that limit sodium uptake by roots, store them in cell <a href="http://en.wikipedia.org/wiki/Vacuole" title="Vacuole" >vacuoles</a>, and control them over long distances;<sup id="cite_ref-58" class="reference" ><a href="http://en.wikipedia.org/wiki/Sodium#cite_note-58" >[59]</a></sup> excess sodium may also be stored in old plant tissue, limiting the damage to new growth.</p>