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Be Sodium-Smart for Healthier Blood Pressure and Bones

We can't exist without sodium, commonly consumed as sodium chloride or salt. Sodium is the main component of the body's fluid found outside of cells and helps carry essential nutrients into cells. But as we all know, getting an excess of this mineral isn't good for our health. As far back as 2,500 B.C., Chinese physicians warned that too much salt would "harden the pulse", and scientists today know that excess sodium contributes to high blood pressure and raises the risk for stroke, heart attack and kidney disease. Though less well understood, high sodium diets may also make older women more vulnerable to bone loss.

Sodium and Potassium Goals for Better Blood Pressure

On average, the higher an individual's salt intake, the higher their blood pressure. It's reported that 95% of American men and 75% of women currently consume salt in excess of the upper intake level of 5.8-6 grams daily set by the Institute of Medicine (1).

So cutting back on salt can result in meaningful public health benefits. For example, a recent review looked at long-term trials that examined the fall in blood pressure resulting from salt restriction. The reviewers concluded that strokes would fall by 13% and ischemic heart disease by 10%, for every 3 grams of salt reduction daily by the general public (2).

The 2005 Dietary Guidelines call for keeping sodium intakes at less than 2,300 milligrams (mg) of sodium daily (3). That's roughly the sodium in a teaspoonful of salt (6 grams salt). Some people are more salt sensitive than others, including those who already have hypertension, Afro-Americans, middle-aged and older adults. These groups should aim for no more than 1,500 mg of sodium each day, and try to consume at least 4,700 mg of potassium daily from foods. A diet high in potassium from produce can help blunt the effects of sodium on blood pressure, and may also reduce the risk of developing kidney stones. Potassium rich fruits and vegetables include green leafy veggies, fruit from vines (e.g. tomatoes), citrus and dried fruits, beans, and root vegetables such as potatoes.

Bones May Benefit Too

Several studies have found that high sodium intakes can increase urinary loss of calcium (4). Researchers have also observed a link between higher blood pressure and greater and faster loss of bone minerals in post-menopausal women (5). Most recently, investigators found that a high salt diet modestly increases the rate of bone breakdown in older women, at least in the short term (6). Many mature women - especially those who don't consume enough calcium - appear unable to adapt to high salt intakes. And that could increase their risk of bone loss over the long term.

Where Is Sodium Coming From?

Most Americans know to be careful with the salt shaker, since only about 10-11% of dietary sodium comes from salt added during cooking or at the table. Most sodium comes from prepared, preserved, processed and fast foods. So it's important to check food labels and watch out for high sodium items such as luncheon meats, soups, canned vegetables and baked products. Better yet, try to choose fresh, unprocessed foods, and go for more potassium-rich produce.

References

1. Dietary reference intakes for Electrolytes and Water. National Academy of Sciences, 2004.
2. He FJ and MacGregor GA, How far should salt intake be reduced: a meta-analysis. Hypertension 42:1093-99, 2003.
3. USDA and HHS Dietary Guidelines for Americans, January 2005.
4. Harrington M and Cashman KD. High salt intake appears to increase bone resorption in postmenopausal women. Nutrition Reviews 61:179-83, 2003.
5. Cappuccio FP et al. Unraveling the links between calcium excretion, salt intake, hypertension, kidney stones and bone metabolism. J Nephrology 13:169-77, 2000.
6. Massey LK. Effect of dietary salt intake on circadian calcium metabolism, bone turnover, and calcium oxalate kidney stone risk in postmenopausal women. Nutrition Res 25:891-903, 2005.