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.