When a person switches to a salt-free diet or consumes very little salt (3–3.5 g per day — this is about 1.1–1.3 g of sodium), a sodium deficiency occurs. Since the physiological need for sodium in an adult is approximately 2–2.5 g per day, and for many it is even higher (depending on the level of physical activity, climate (sweating), health status, and other factors).
What happens with a sodium deficiency:
The compensation mechanism through the kidneys is activated. The kidneys receive a signal about the sodium deficiency through the renin-angiotensin-aldosterone system (RAAS). In response, they begin to actively reabsorb sodium from the primary urine back into the blood to compensate for the deficiency.
Sodium reabsorption leads to water retention. Since sodium is osmotically active, its reabsorption is always accompanied by the absorption of water.
For approximately every gram of reabsorbed sodium, the body additionally retains up to 1 liter of water. This is explained by the fact that sodium retains water in the vascular system and in the interstitial (intercellular) fluid.
Edema develops. Constant fluid retention leads to the accumulation of water in tissues (edema), both in subcutaneous fat and in organs.
The load on the cardiovascular system increases. The increase in circulating blood volume raises blood pressure, leads to heart overload (especially in the elderly and people with heart failure), and contributes to the development of hypertension.
Additional consequences of prolonged sodium deficiency:
- chronic fatigue (due to impaired neuromuscular transmission);
- muscle cramps;
- headaches (due to cell hypohydration during hypovolemia);
- hyponatremia, which in severe cases is life-threatening (seizures, altered consciousness, coma).
Key physiological paradox
When there is little salt — the body tries to retain it at any cost, even at the expense of accumulating excess water.
When there is enough salt — the balance is maintained more easily: excess sodium is easily excreted, and water is not retained.
For most people, the physiological norm is considered to be 5–7 g of salt per day (that is, 2–2.8 g of sodium), and in hot climates and with intense physical activity — even more.
