Excess dietary intake of common salt (Sodium Chloride) is a known risk factor for high blood pressure (hypertension). In people with high blood pressure, a reduction in blood pressure is observed after reducing daily dietary salt intake. Currently, the recommended daily dietary intake for sodium chloride is <6 g. Increased dietary intake of sodium also augments the increase in blood pressure caused by other risk factors.
Sodium chloride causes an increase in the volume of fluid in the blood vessels, and this results in an increase in the blood pressure. The increased blood pressure causes an increased excretion of sodium by the kidneys, thus maintaining the sodium balance in the body. However, this is an oversimplified explanation and exact mechanisms by which these changes occur are still a topic of active research. If the sodium excretion capacity of the kidney is impaired for any reason (e.g. kidney disease, increased salt-retaining hormone), the blood pressure may increase to even higher levels to achieve the excretion of excess sodium.
The sensitivity to salt is variable. Some people are more sensitive than others, and they may show marked increase in blood pressure with increased dietary intake of sodium chloride. The difference in the sodium excretion capacity of kidneys may be one of the reasons behind different susceptibility of every individual to common salt’s blood pressure raising effects.
High dietary intake of salt not only increases blood pressure but also has other adverse health effects like left ventricular hypertrophy (independent of that due to high blood pressure), stroke, kidney damage, worsening of heart failure, renal calcium stones and osteoporosis.
It is important to note that only the common salt, i.e. sodium chloride is known to increase the blood pressure. Non-chloride salts of sodium don’t raise the blood pressure, thus sodium alone is not the culprit. The salts of potassium, magnesium and calcium might result in decrease in blood pressure. In some studies, dietary supplementation of potassium and calcium salts has been found to have some antihypertensive effects, and they are currently being evaluated for adjunctive therapy.
Reducing daily intake of common salt is one of the lifestyle modifications suggested for the management of high blood pressure. Reducing dietary sodium chloride intake to less than 6 g per day results in an approximately 4-5 mm of Hg reduction in systolic blood pressure and 1-3 mm of Hg reduction in diastolic blood pressure. This dietary reduction is also beneficial in prehypertensive people and reduces the risk of future cardiovascular events.
The blood pressure lowering effects of reduced dietary intake are more pronounced in elderly and obese people. Greater blood pressure lowering effect can be obtained by combining reduced salt intake with antihypertensive medications or other lifestyle modifications like regular aerobic exercise, reducing alcohol intake, smoking cessation, taking a healthier diet, reducing weight, etc.
Processed, packaged and restaurant foods have a high amount of common salt and thus should be avoided. One should try to minimize the use of salt in cooking and avoid adding additional salt from the table. Eating more fresh fruits, vegetables and dairy products also reduces the net daily intake of common salt. Dairy products are rich source of calcium while fruits and vegetables are rich source of potassium and magnesium. A diet rich in calcium, magnesium and potassium helps in reduction of blood pressure. However, supplementation with calcium, magnesium or potassium salts is currently not recommended in people with raised blood pressure. They are also not currently recommended for prevention of future development of hypertension in people with normal blood pressure.