What are the risks and benefits of mammograms?

DEAR READERS: In yesterday's column, I answered a question from a 47-year-old woman who had never had a mammogram and wondered if she should have one. She had heard that one group of experts -- the American Cancer Society (ACS) -- had recently changed its recommendations on this issue.

When should I start getting mammograms?

DEAR DOCTOR K: I'm a 47-year-old woman who has never had a mammogram. Some experts recommend I get one, but others do not. I understand that the American Cancer Society recently updated its recommendations about breast cancer screening. Does it say I should have a mammogram? If so, which experts should I believe?

DEAR READER: I'm surprised when people are bothered by medical experts having different opinions. Expert politicians, expert lawyers, expert architects -- experts of all kinds disagree with each other all the time. Why? Because it is rare for the "truth" of any question to be clear beyond dispute.

Can brain stimulation devices help improve memory and thinking?

DEAR DOCTOR K: I saw an ad for something called a "tDCS brain-stimulating device." It supposedly helps improve memory and thinking. Is it worth a try?

DEAR READER: Transcranial direct current stimulation (tDCS) transmits a current into the brain through electrodes (little metal plates) on the forehead or scalp. The current is weak; it comes from a 9-volt battery (the size used in a smoke detector). People who undergo tDCS may feel their scalp tingle and hear a humming noise. Doctors can control whether the current activates -- or suppresses -- the neurons in your brain that lie beneath the electrodes.

How can I protect my daughter from lead poisoning?

DEAR DOCTOR K: A friend's daughter got lead poisoning from paint in her house. What can I do to protect my kids?

DEAR READER: Lead is poison. Although major strides have been made in the past 50 years, lead poisoning is unfortunately still a problem. All of us are exposed to lead, but children are most vulnerable to it.

What will happen during my pulmonary function tests?

DEAR DOCTOR K: My doctor ordered breathing tests to see if I have asthma. He didn't tell me what it's like to go through this. Can you explain?

DEAR READER: The tests your doctor almost surely is referring to are pulmonary function tests. The tests are painless. You breathe in and out through a tube that is connected to various machines.

Why do dentists recommend chewing gum?

DEAR DOCTOR K: Why do dentists recommend chewing gum? Doesn't gum cause cavities?

DEAR READER: Dentists don't recommend just any chewing gum. They recommend sugar-free gum, specifically gum that contains xylitol, a sugar-free, no-calorie sweetener made from the bark of birch trees. It may actually lower your risk of tooth decay and cavities by interfering with the growth of harmful mouth bacteria.

Are organic foods healthier than non-organic?

DEAR DOCTOR K: Many of my friends buy only organic foods. But are they really healthier than non-organic?

DEAR READER: Organic crops are grown without most synthetic fertilizers and pesticides. Organic animal products are free of antibiotics and hormones. Many people believe these foods are better for them. But we really don't know that they are.

How can I stay as active as possible as I get older?

DEAR DOCTOR K: I'm in my 80s, and I've lost some mobility over the years. How can I continue to stay as active as possible?

DEAR READER: Most of us take for granted the stamina, strength, balance, coordination and range of motion needed to perform even simple acts such as getting out of bed, heading down the stairs and walking around the block. But when we lose these basic skills, we begin to understand how much of living well relies on being able to move.

Does breath focus help to relieve stress?

DEAR DOCTOR K: A friend recommended a technique called "breath focus" to help me deal with stress. Does this help?

DEAR READER: Breath focus is a simple yet powerful technique that can elicit the "relaxation response," a state of profound peace and rest. The relaxation response was popularized by my colleague at Harvard Medical School, Dr. Herbert Benson. It has given all of us a weapon against stress.

Are cochlear implants a type of hearing aid?

DEAR DOCTOR K: I'm hard of hearing and want to learn more about cochlear implants. Are they a type of hearing aid?

DEAR READER: A cochlear implant involves several small electronic devices that are surgically implanted in the ear. It can provide sound to people who are severely hard of hearing or deaf. It is not a type of hearing aid. In fact, to be eligible for a cochlear implant, a person must have hearing loss in both ears that is so extreme that even the best hearing aid has little or no effect.