Saturday, October 31, 2009

How Much is Too Much Salt

How Much Sodium Is Too Much?

David L. Katz, MD
Photo: Mackenzie Stroh
Q: I'm 50 years old, and I love salt. My blood pressure is normal. I eat a very healthy diet with lots of fruit and veggies. Do I really need to watch my sodium intake?
— Shannon Dolph, Portland, Oregon

A: Given all the warnings about sodium raising blood pressure, you might think the link between the two is crystal clear. Actually, it's still a bit out of focus. One reason for the lack of clarity is that salt sends some people's blood pressure soaring while others seem able to tolerate heaps of it, no harm done. This inconsistent response has led to the notion of salt sensitivity, a trait generally thought to occur in at least 10 percent of the population. So far there's no easy way to test for salt sensitivity—or its absence (though researchers seem to be narrowing in on a "salt gene"). And since several studies suggest that most people benefit to varying degrees from minding their sodium intake, public health officials keep things simple by recommending that everyone cut back on salt. Besides, high blood pressure isn't the only concern: Even when blood pressure remains normal, high-sodium diets have been linked to heart disease (the theory is that excess sodium can directly damage the arteries and heart). And high-salt diets may rob your bones of calcium, potentially weakening bones and leading to osteoporosis.

But you may not need to worry if you eat a healthy diet and prepare most of your own meals: Five percent of the sodium in the average American's diet is added during cooking, 6 percent comes from the shaker on the table, another 12 percent occurs naturally in food, and the remaining 77 percent comes courtesy of processed, prepackaged foods. Cook your meals using fresh, whole ingredients and you'll get only a quarter of the 4,000 milligrams of sodium the typical American consumes in a day. That would put you well under the recommended daily limit of 2,300 milligrams.

One last note: Sodium can turn up in surprising places. That big, healthy-looking bran muffin on the coffee-shop counter can pack nearly 800 milligrams. Some breakfast cereals deliver up to 600 milligrams a bowl. Highly processed, sweetened foods may conceal a great deal of sodium and not taste salty at all.

Q. I use a lot of sea salt when I cook. Is it possible I could be falling short on iodine? —Ann Marshall, Greenville, South Carolina

A. It's unlikely, though recent research suggests that iodine deficiency isn't as rare as it once was. Adults need 150 micrograms a day, which we used to get easily from our diet. But in recent years, some of our main sources—restaurant and processed food—are less likely to contain iodized salt. We also get iodine from fish, shellfish, strawberries, yogurt, cow's milk, and eggs. Kelp contains the most, so sushi eaters get plenty. But it isn't wise to eat fish every day, and you need a constant supply of iodine because your body can't make or store it. The amounts in dairy vary, so keeping iodized salt on the table and using it occasionally in cooking can help prevent shortfalls.

A deficiency leaves your body unable to synthesize thyroid hormones. The gland will compensate by straining to produce more hormones, possibly leading to fatigue, depression, weight gain, and eventually a goiter—an enlarged, overworked thyroid.

While most American adults get enough, pregnant and breastfeeding women, infants, and children could be low, and they need it the most: Iodine is crucial for brain development. (Concerned mothers should check that their prenatal and postnatal vitamins deliver at least 150 micrograms a day.) If you are worried about your iodine intake or your thyroid, ask your doctor to check your level of TSH—thyroid-stimulating hormone. If it's normal, you'll know that your thyroid is happy with your iodine intake. If your TSH level is abnormal, you doctor will help you figure out why and whether the solution lies in your saltshaker.