Body metabolizes caffeine slower as you age

We're doing a double take as we look at the calendar, which says autumn has arrived. How did the summer fly by so fast? You've kept our mailboxes full, so we will dive right in.

• In response to a column about how diet affects sleep, a geriatric care nurse from Nebraska added the topic of caffeine to the conversation. She pointed out that many adults metabolize caffeine more slowly as they age, so even one afternoon cup of coffee can interfere with that night's sleep. "When I share this with clients, they invariably say they can't manage without at least one cup a day," she wrote. "It's true that without a few weeks of weaning - fewer cups, then half-caf, then decaf, then no caffeine - the body complains. But for these people, the choice comes down to caffeine or sleep." Thank you for making that important point.

• Regarding a column that discussed melatonin as a sleep aid, a reader asked about dosage. "The column states the recommended beginning dose is .05 milligrams, but the pills don't come in that small dosage," she wrote. "Did you actually mean 0.5 milligrams?" The answer is yes, the lower end of the recommended dosage is indeed 0.5 milligrams. We're grateful to you for pointing out that misplaced decimal point. To recap - although there is no official recommended melatonin dosage, a range of 0.5 milligrams to 3 milligrams is considered safe and adequate to promote sleep in adults.

• After a column about newly pierced ears and infection, we heard from a reader in Pennsylvania. She experienced the redness, itching and soreness we mentioned, but for an entirely different reason. "I went to my doctor, and it was determined I was probably allergic to nickel in the earring post," she wrote. "Although the earring was advertised as 'surgical steel,' some amount of nickel can still be present. Until then, I was unaware of a nickel allergy." Nickel is a frequent cause of metal allergy, and even a small amount can lead to contact dermatitis. Titanium and 14k gold are both good options for new piercings.

• A reader from Alaska asked about biotin, which is one of the B vitamins. We had discussed how biotin can interfere with certain lab test results, including those used to diagnose heart attack. "Is there a safe amount of time where one could stop taking a multivitamin with 30 micrograms of biotin and not have it be a factor?" he asked. There's no recommended daily allowance for the vitamin, but the 30 mcg you're getting in your daily multivitamin is considered reasonable. Unless someone is taking megadoses of 5,000 mcg or more, it is believed that stopping the vitamin for 72 hours should be adequate. That said, always let your doctor and the lab know about your biotin intake whenever tests are scheduled.

• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.