People’s Pharmacy: A big dose of biotin for brittle fingernails

Q. I have found that 5,000 micrograms of biotin daily is a miracle drug for my weak, brittle fingernails. My dermatologist recommended this. Also, because of previous skin cancer, I wear sunscreen whenever I am outside. My family doctor told me to take 2,000 IU of vitamin D3 to get my level up to the normal range. I am a healthy, active man, so I plan to continue with my current supplements.

A. Thank you for sharing your experience with biotin, a B vitamin. The federal Office of Dietary Supplements notes that an adequate daily intake of biotin for adults is 30 mcg. It goes on to state: “Signs of biotin deficiency include skin rashes, hair loss and brittle nails. Therefore, biotin supplements are often promoted for hair, skin and nail health. However, these claims are supported, at best, by only a few case reports and small studies.”

Even though you are taking a high dose of biotin, this nutrient appears safe. That said, it can interfere with lab tests. Biotin artificially lowers the results of TSH and 25-hydroxyvitamin D tests. If you ever need to have blood drawn, make sure the lab knows you are taking biotin.

Q. If I’m not mistaken, some over-the-counter antihistamines have anticholinergic activity. Before reading that anticholinergic drugs could be bad for the brain, I’ve taken these for sleep a few nights in a row. For several weeks afterward, I experienced memory problems and migraines.

The yardman at my condo complex has been taking these drugs for years, and he barely has any mind left. He can’t remember much of anything and apparently is not aware of it because he doesn’t write things down. I believe a few customers have scolded him about this, but he apparently forgets that, too. I can hardly wait until he retires.

A. Diphenhydramine is a sedating antihistamine that is almost always included in nighttime pain relievers. It is the “PM” in products like Advil PM, Aleve PM or Tylenol PM.

Diphenhydramine has anticholinergic activity. That means it alters the action of a brain chemical called acetylcholine, which is crucial for cognitive function and memory. Geriatricians discourage the use of anticholinergic drugs in older patients because they can contribute to impairment.

Our Guide to Drugs and Older People has a list of medications that may be inappropriate for seniors. Anyone who would like a copy, please send $3 in check or money order with a long (No. 10), stamped (70 cents), self-addressed envelope to: Graedons’ People’s Pharmacy, No. O-85, P.O. Box 52027, Durham, NC 27717-2027. It also can be downloaded for $2 from the Health eGuide section of our website: peoplespharmacy.com.