Salt and blood pressure

Excess salt intake tends to increase blood pressure, particularly in African Americans, older persons, obese persons, and people in general who are susceptible to developing a problem regulating sodium concentration in the body. This last group is termed “sodium sensitive” because they are not good at excreting excess salt via the kidney. This excess salt retention has some tendency to increase blood pressure in these people. It is not clear whether the sodium ion or the chloride ion is most responsible for the effect. If one reduces sodium intake, chloride intake naturally falls; the opposite is also true. For the most part, when nutrition recommendations suggest consuming less sodium that is equivalent to saying consume less salt. Since only some North Americans are very susceptible to increase in blood pressure from salt intake, it is likely only the lifestyle factor related to hypertension. Thus, it is unfortunate that salt intake receives the major portion of public attention with regard to hypertension; obesity, inactivity, and alcohol abuse should be given much more attention. This is especially true for people who are not sodium sensitive. Again, about half the people with hypertension are not. However, many people with hypertension do not know whether they are not sodium sensitive, and testing for this sensitivity takes a lot of time and is not routinely done.

The latest dietary advice from the Dietary Guidelines for Americans and the American Heart Association suggests that adults consume no more than the Daily Value for sodium (2400 mg). Currently, North Americans consume daily, an average, almost double that amount (4 to 7 g). Both sets of recommendations note that there is no risk in reducing sodium intake to the Daily Value.

The exact mechanism whereby sodium increases blood pressure is not clear. Studies suggest that there is a genetically influenced ability that determines the ease at which the body can excrete sodium. In salt sensitive individuals, the kidneys require a higher blood pressure in order to excrete sodium from the body, compared with salt-resistant people. This causes salt-sensitive individuals to retain more sodium. This sodium retention in the body then leads to increased blood volume and, in turn, the increased blood pressure needed to maintain sodium excretion.

Physicians usually resort to a combination of antihypertensive medications, such as diuretics and modern sodium restriction (3-4g/day) as an initial form of therapy. This combination typically reduces blood volume, and therefore, is often effective in controlling blood pressure.

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