DEAR DR. ROACH: I have low thyroid levels. My blood tests say that the levels are OK, but I still have all the symptoms. I received biological hormones, which helped a lot, but yams bind to the levothyroxine pills.

• S.P.

ANSWER: The symptoms of low thyroid levels can be very nonspecific. Fatigue or weakness, intolerance of cold temperatures, and weight gain are common, but many conditions (anemia is a big one) can cause these as well.

In my general internal medicine practice, I see a lot of normal thyroid tests because so many conditions can resemble low thyroid levels. If the thyroid tests are normal, though, then it’s very unlikely that the thyroid is the cause of the symptoms.

There are a handful of exceptions, such as people who have normal T4 levels (T4, or thyroxine, is the mostly inactive precursor to T3, which is the most active form of the hormone) but are unable to convert T4 to T3, leading to symptoms of hypothyroidism with normal T4 levels. Unless the doctor checks their T3 levels, they can miss this diagnosis, which is uncommon but not rare.

I do see that yams can block the absorption of thyroid hormones, but this is true only when eaten raw and in large quantities. So, most people do not need to worry about this.

In my opinion, you should get your T3, T4 and TSH levels checked. But if they are normal, you need to find out what else might be causing your symptoms.

DEAR DR. ROACH: I have been taking a fiber supplement successfully for a while, which is known to several of my doctors. A new doctor now advises that this well-known brand contains lead, and I should discontinue its use. She recommended a different supplement, which I have tried. Unfortunately, it does not work as well as my original brand.

Please clarify whether fiber supplements do in fact contain lead.

• A.B.

ANSWER: A 2024 report by an independent laboratory found tiny lead levels present in all the psyllium products they tested. Lead is found throughout the environment, and the average American ingests about 5 mcg of lead daily.

The supplement you mentioned contains about 1-2 mcg if taken at the maximum daily dose. The supplement your new doctor recommended has less. The Food and Drug Administration limit is 12.5 mcg/day based on a safety factor of 10.

The exceedingly small amount that is present in your brand does not justify using a product that doesn’t work as well, even if it has an even smaller amount. It is very unlikely that the amount of lead present in the supplement will cause you any health problems.