Sodium-rich diets can cause damage beyond high blood pressure

Holiday brunches, buffets, dinners, and parties are often laden with salty food. For some people, a high-salt diet leads to high blood pressure, which makes the heart work harder and increases the risk of having a heart attack or stroke, or of developing heart failure or kidney disease. Other people are blessed with genes or physiology that lets them eat foods high in sodium without ever seeing a bump in their blood pressure. If you’re in the latter camp, is it OK to blithely eat ham, cheese logs, and other salty holiday foods?

No. As my colleagues David Edwards, Claudine Jurkovitz, William Weintraub, and I wrote in the Journal of the American College of Cardiology, too much sodium in the diet can damage health even when blood pressure stays normal.

By weight, salt is about 40 percent sodium. The human body needs some sodium to transmit nerve impulses, contract and relax muscles, and balance fluids throughout the body. The average person needs less than 500 milligrams of sodium a day to survive, but gets about 3,400 milligrams, nearly seven times what’s needed.

Very high dietary sodium appears to be especially harmful to blood vessels. It damages their innermost layer, called the endothelial layer. This thin sheet of cells helps blood vessels dilate to increase blood flow when the need arises. Damage to the endothelial layer sets the stage for atherosclerosis, the main artery-clogging disease process underlying nearly all cardiovascular problems, including heart attacks and poor blood flow to the legs and brain. Atherosclerosis can also cause kidney problems and vascular dementia.

Even when sodium doesn’t boost blood pressure, too much of it in the diet can:

• Harm the heart. Too much sodium can increase the size and the thickness of the left ventricle, the heart’s main pumping chamber. This makes it harder for the heart to efficiently circulate blood around the body.
• Damage the kidneys. In lab animals, diets high in sodium make it more difficult for the kidneys to filter blood. Lots of sodium also increases the level of blood markers of kidney damage.
• Affect the brain. A diet high in sodium can “sensitize” cells in the brain that are part of the sympathetic nervous system, which controls the body’s so-called fight or flight response. This sensitization creates a greater-than-usual blood pressure response to stress.

How much sodium is too much?

The average American consumes about 1 ½ teaspoons of salt (3,400 milligrams of sodium) a day. Most of this comes from the highly processed foods that we routinely eat. For example, a slice of pizza has approximately 600 milligrams of sodium. A serving of canned chicken noodle soup delivers more than 800 milligrams.

The current Dietary Guidelines for Americans recommend that younger, relatively healthy individuals get no more than 2,300 milligrams of sodium (1 teaspoon of salt) a day, while everyone over age 51 and those with high blood pressure, diabetes, or kidney disease should take in 1,500 milligrams a day. One element of the American Heart Association‘s definition of ideal cardiovascular health is a diet that contains less than 1,500 milligrams of sodium a day. While there is some inconsistency in what the upper daily limit should be, what’s important right now is that most Americans should cut back on the amount of sodium they take in.

Earlier this month, New York City started requiring large chain restaurants to label salty dishes that contain more than 2,300 milligrams of sodium — the upper limit of what you should get over the course of a whole day. The salt-shaker-in-a-black-triangle “sodium bomb” warning is intended to nudge diners toward less salty and presumably healthier dishes.

Avoiding sodium bombs is one way to optimize long-term cardiovascular health. Recent evidence suggests that a single high-sodium meal can temporarily impair blood vessel function. So staying away from high-sodium meals is important for everyone, even for those who don’t have salt-sensitive blood pressure. Cutting down on daily sodium intake requires eating less processed foods and more fresh foods. Food items that contain a lot of sodium include cold cuts, many soups, and condiments such as ketchup and soy sauce.

It will be interesting to see if sodium labels in New York City restaurants will nudge New Yorkers toward healthier choices. Whether or not they do, it’s a good idea for almost everyone to cut back on sodium during the holidays and beyond.

William B. Farquhar, PhD, is professor and chair in the department of kinesiology and applied physiology at the University of Delaware. He studies the role of diet and exercise on human health.