A low-salt diet is beneficial for certain people with cardiovascular disease. Preliminary evidence has linked salt consumption with increased cardiovascular disease incidence and death among overweight people. Low-salt diets seem to be especially important for people with hypertension (high blood pressure). Salt intake has been definitively linked to hypertension in Western societies, and minimizing salt consumption lowers blood pressure in many people.
Research studies consistently find that increased dietary salt aggravates asthma symptoms, especially in men. In a small, preliminary trial, men with asthma who doubled their salt intake for one month experienced a worsening of their lung function. Although not all of the observed effects were conclusive, several double-blind trials have provided evidence of clinical improvement following a period of salt restriction.
Other conditions that may benefit from a low-salt diet include Meniere's disease, migraine headaches, kidney stones, gastritis, and ulcers caused by H. pylori infection. Preliminary evidence also suggests that restricting dietary salt may play a role in the prevention of certain types of cancer, including stomach, colorectal, and head and neck cancers.
Restricted levels of salt may help to preserve bone density. Short-term increases in dietary salt result in increased urinary calcium loss, which suggests that over time, salt intake may cause bone loss. Increasing dietary salt has increased markers of bone loss in post- (though not pre-) menopausal women.
Lower salt intake may also help to protect against the development of reduced insulin sensitivity, a physiological process that can lead to blood sugar regulation problems in certain people. Preliminary studies suggest that high salt intake decreases insulin sensitivity in young, healthy people, but not in older people with hypertension. Moderate restriction of salt, however, also decreased insulin sensitivity in one preliminary study of healthy people, but had no effect in other studies of people either with or without hypertension.
Salt restriction also may be helpful in reducing edema in some people. High salt intake tends to lead to water retention that may promote the further accumulation of fluid beneath the skin.
Pregnant women who are experiencing hypertension of pregnancy should not follow a low-salt diet. A low-salt diet has not been shown to have a significant effect in reducing blood pressure during pregnancy, so salt restriction is not recommended to women with gestational hypertension and preeclampsia. Additionally, unlike other conditions that cause high blood pressure, salt restriction (and use of diuretics) can worsen preeclampsia by reducing blood flow to the kidneys and placenta. In preeclampsia, unrestricted use of salt and an increased consumption of water are needed to maintain normal blood volume and circulation to the placenta.
People with certain conditions have been found to benefit from salt intake and should not follow a low-salt diet. Children with cystic fibrosis lose a large amount of salt in their sweat and thus should be encouraged to salt their food liberally. Chronic fatigue syndrome sufferers who have a form of low blood pressure triggered by changes in position (called orthostatic hypotension) have been reported to be helped by additional salt intake. Additionally, people with goiter or hypothyroid condition should not restrict intake of iodized salt if it is their only major source of iodine.