Dear Doctor: I just turned 65, and my doctor wants me to have a bone density test. What is it, and how does it work?

Dear Reader: A bone mineral density test, or BMD, measures the strength of one’s bones. It’s an important diagnostic tool for osteoporosis, a progressive disease in which bones become brittle and fragile and can easily break.

Although our bones appear hard and static, they are made up of living tissue. The honeycombed inner framework of a bone is composed of collagen, which is a protein. A mineral known as calcium phosphate provides strength and solidity. Together, these two substances create a strong and flexible structure that successfully withstands stress.

Our skeletons have a dynamic life cycle in which old bone is continuously removed, while at the same time new bone is added. In children and teens, the addition part of the cycle outpaces removal, allowing the skeletal bones to grow in both strength and density. This cycle peaks sometime in our late 20s, at which point bone reabsorption gradually begins to overtake bone formation. Certain hormonal changes that occur in women during menopause further accelerate that imbalance. The result is that old bone may be removed too quickly, new bone may be added too slowly, or both. Over time, the honeycomb framework within the bone grows increasingly porous, while the exterior structure becomes thinner.

All of this leads us back to the scan your doctor has recommended. Known as a DXA test -- that’s short for dual-energy X-ray absorptiometry -- it’s essentially the same procedure and technology used in a standard X-ray. A machine delivers low-dose X-rays, which measure the amount of calcium and other bone minerals present in a segment of bone. The proportion of bone minerals to soft tissue reveals bone density.

The DXA test, which is most often used to measure bone density at the hip and the lumbar spine, is used to diagnose osteoporosis. It can also help assess risk of future fractures, and to detect whether a treatment for osteoporosis is working. The test, which is as quick and painless as an X-ray, is performed on an outpatient basis. It takes from 15 to 30 minutes to complete, depending on the part of the body being scanned. The results of the test, known as a T score, are presented as a comparison between your own bone density and that of a young adult at the peak of bone formation. A second measurement, known as a Z score, compares your bone density to people your own age, size and gender.

The BMD test is usually recommended for women when they turn 65. It may be recommended earlier than that if a woman has rheumatoid arthritis, low body weight or low vitamin D levels; has used a corticosteroid for three or more months; has a family history of osteoporosis; has experienced bone breaks resulting from a minor accident; has lost height; or is a heavy smoker or drinker. Depending on the results of the initial test, a followup test may be needed in one or two years.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My wife overindulged on her birthday and wound up with a pretty fierce hangover -- headache, nausea, brain fog, the works. She got so much weird advice that it got us to wondering, what exactly is a hangover? Are there any remedies that actually work?

Dear Reader: Your question is one for the ages -- literally. References to the unique state of distress we call a hangover date back thousands of years. So does the quest for a cure. Yet despite the best efforts of modern science, the cause of a hangover -- as well as a remedy -- remains unclear.

Let’s start with what we do know. A hangover occurs when you drink too much alcohol. For some, a few glasses of wine can lead to profound regret the morning after. For others, getting a hangover takes a night of excessive drinking of hard liquor. No matter the amount of alcohol, the symptoms remain the same. These include the headache, nausea and cognitive issues that your wife suffered from, as well as dry mouth, thirst, fatigue, dizziness, vertigo, diarrhea, tremors, disturbed sleep, rapid heartbeat, excessive perspiration, anxiety, low mood and sensitivity to light and sound.

Research suggests that genetics play a role in how much you can drink before you’ve earned yourself a hangover. So do a person’s age, sex and physical health; the state of their immune system; and how quickly they drink. The specific type of alcohol may also be a factor. Darker-colored drinks -- such as bourbon, dark beer and red wine -- contain higher concentrations of compounds known as congeners. The body metabolizes these into toxic substances such as formaldehyde and formic acid, which can add to hangover misery.

Dehydration was long considered a prime culprit in hangover symptoms, but recent research has found no difference in electrolyte levels among people who are hung over and those who are not. Although a toxic compound known as acetaldehyde, produced when the body breaks down ethanol, had been implicated in hangover misery, more recent research now points to the role of cytokines. These are small proteins associated with inflammation, which the immune system uses for signaling. The theory is that drinking triggers the release of cytokines, which in turn unleash the full fury of the immune system.

As for how to cure a hangover, science hasn’t gotten that far. The best you can do is manage the symptoms for the eight to 24 hours it takes for a hangover to play out. First, skip hair-of-the-dog therapy. More alcohol may give a temporary boost, but soon enough leads to the throes of even more misery. Instead, drink plenty of water, eat complex carbs to boost low blood sugar and fend off nausea, use antacids if needed for stomach upset, and get some sleep. Aspirin and other non-steroidal anti-inflammatories can help with headache, but can also irritate the stomach. Never take Tylenol during or right after drinking, as it can cause liver damage when mixed with alcohol. No one who has ever had a hangover wants to hear this, but the only certain cure is time.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I keep reading about stents, and how it turns out they’re no better for blocked arteries than heart meds. How does something like that get decided?

Dear Reader: You’re referring to the findings from a large international study that evaluated various medical interventions for patients with blocked coronary arteries.

Before we get into the study, we should first talk about coronary artery disease. This is a condition in which the vessels that supply the heart muscle with oxygen-rich blood become blocked. A substance called plaque -- which is made up of cholesterol, calcium, fat and other cells -- collects along the inner lining of the arteries and causes them to narrow. This limits the blood flow in the arteries, and, in some cases, can cut it off entirely. When the flow of oxygen-rich blood to the heart slows or stops, the results can range from chest pain, irregular heartbeat and shortness of breath, to heart attack, to an increased risk of stroke. Bits of the hardened plaque can also break free and cause blood clots, which can also limit or stop blood flow.

Coronary artery disease is the most common type of heart disease in the United States. According to the Centers for Disease Control and Prevention, it accounts for more than 370,000 deaths each year. It’s a serious problem, and researchers have spent decades looking for solutions. These include bypass surgery and the use of stent intervention, which were evaluated in the study.

In bypass surgery, a surgeon uses a blood vessel taken from another part of the patient’s body to route the flow of blood around the blocked artery. A less invasive option is the stent, which is a tiny mesh tube implanted into the artery via a long, flexible tube known as a catheter. The surgeon inserts the catheter into an artery in the arm or groin and then, with the help of a special X-ray machine, guides it through the blood vessels until it reaches the desired area. Once in place, the rigid stent physically opens and supports the artery walls, which allows normal blood flow.

The study you referenced, led by Stanford University and New York University, assessed the medical outcomes of more than 5,100 patients living with moderate to severe coronary artery disease. Researchers divided the study participants into two groups. One group underwent bypass surgery or received a stent. Participants in the other group were prescribed heart medication and instructed to make lifestyle changes, including regular exercise, a healthy diet and quitting smoking. Researchers then followed both groups for between 18 months and seven years, and tracked any cardiac events.

At the end of the study, researchers found that the surgical procedures proved more successful than medication alone at alleviating exercise-related chest pain. However, in the long run, they saw no difference between the two groups when it came to major coronary events, such as hospitalizations, heart attacks and death. In these instances, medication and lifestyle were as effective as surgical interventions. Whether these new findings help settle what has long been a fierce and sometimes contentious debate about treating coronary artery disease remains to be seen.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)