Dear Doctor: Can you explain probiotics? Who should take them, and are they harmful in any way? They seem helpful to me in calming my stomach.

Dear Reader: For many generations, society feared bacteria, seeing only the devastation that bacterial disease created. Today, with the advent of antibiotics, we have been able to cure infections that once led to illness and death. However, our primary tool -- drugs known as antibiotics -- also indiscriminately kill bacteria that don't cause disease. Only recently have we come to realize how important these non-dangerous microorganisms are to our health. With an estimated 40 trillion bacteria in and on the human body, outnumbering the 30 trillion to 37 trillion cells that make up the body, it's clear that a symbiotic relationship with these organisms is important to our health.

To answer your question about probiotics, first let us look at gastrointestinal bacteria. Many probiotic preparations promise to help replenish beneficial bacteria in the colon, with the theory being that they increase the health of the intestinal lining, suppress inflammation caused by damaging bacteria, and reduce inflammation caused by an overactive immune system. Most probiotics contain species of the familiar bacterial strains known as Lactobacillus and Bifidobacterium, but some preparations also contain beneficial strains of Streptococcus and Clostridium, or even yeast (Saccharomyces boulardii).

In a 2008 study of 224 children with a diarrheal illness related to rotavirus, participants took either a probiotic preparation (containing various strains of Lactobacillis, Bifidobacterium and Streptococcus) or a placebo. On the second and third days of the illness, the group that took the probiotic had a decrease in stool frequency, improved stool consistency and less need for either oral or intravenous rehydration. A 2002 analysis of nine studies that used Lactobacillus for childhood diarrheal illness found an average reduction of illness of 0.7 days in children who took the probiotic.

A 2010 review of 63 studies assessed the impact of different probiotics on acute diarrheal illness; 56 of these studies looked only at children and infants. On average, probiotics decreased the duration of diarrhea by 24 hours and decreased stool frequency by the second day. Although the authors could definitely say there was benefit in children, they could not conclude if these benefits occurred in adults.

As for more chronic illnesses, a 2009 analysis of 16 studies of people with irritable bowel syndrome found that two studies using Bifidobacterium infantis showed a decrease in abdominal pain, bloating and bowel movements. The other studies were considered methodologically flawed, so the authors couldn't assess the probiotics' benefits.

Probiotics have had mixed results in Crohn's disease, but have shown benefit among people with mild to moderate ulcerative colitis, again through the probiotic preparation.

Similarly, some studies have found benefit from probiotics given with antibiotics, which kill the "good" bacteria as well as the "bad" and therefore increase the risk of Clostridium difficile infection. Not all studies show such benefit, but I would consider probiotics if you've developed diarrhea in the past when taking antibiotics.

One potential issue with probiotics is that, unlike medications, they're not regulated, so there is no true way to know exactly what you're getting. Some patients do develop bloating with probiotics, but for the most part the preparations are well-tolerated. If they're helping you, it seems prudent to continue using your current brand.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: How do I get the most out of my relationship with my primary care physician? The appointments are so short these days, and I want to be smart about the way I use the time.

Dear Reader: That's a great question. As fellow patients who see our own physicians, we share your concerns. And as primary care physicians, we are keenly aware of the need to structure an office visit to make every minute count.

Here, drawn from what we do in our own practices, as well as thoughts from fellow physicians, are some ideas to help maximize the time you have with your physician.

-- Consider timing: Be strategic when making your appointment. Monday and Friday tend to be busiest. The first appointments of the morning are least likely to have a wait time, and your physician won't be feeling as rushed. And please, arrive early!

-- Plan ahead: Write down and prioritize your health concerns. Be prepared to describe them succinctly. Symptoms can be physical, mental and emotional. Include details like when the symptom began, how long it lasts, anything that makes it better or worse, and what you are worried about.

-- Look at the big picture: Bring a complete list of the medications you are taking, including supplements. Be sure to include specific dosages. If it's easier, bring the bottles themselves. If you have recently stopped taking a medication, be sure to include it in the list as well. If you have undergone testing with other providers, tell your primary care physician what prompted the tests and provide a copy of the results.

-- Be a partner: Let your physician know your specific goals for the visit. This allows him or her to manage time wisely and efficiently. Take notes. A lot of information is imparted during a medical appointment, and it's easy to miss important details. Some patients bring a spouse, relative or friend to be another set of eyes and ears.

-- Be assertive: If your physician says something you don't understand, ask him or her to repeat it. If you feel you are not being understood or heard, say so. When you require more time than a visit allows, ask whether a nurse or physician's assistant in the office is available to further answer your questions.

-- Stay focused: Stick to the topic that brought you to the office. Spending the time delving thoroughly into your main health concerns will have the highest yield.

-- Stay connected: Ask your physician for the best way to reach him or her in the next few days, when new questions are likely to arise. Here at UCLA, we have a patient portal that allows our patients to reach us directly via email. Ask your physician whether that's an option. If not, learn your physician's preferred approach, which includes how to reach him or her in an emergency.

-- Keep the conversation going: If you feel your questions or concerns haven't been met, don't be afraid to schedule a follow-up visit.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I'm 71, and after a recent bone scan, my doctors are insisting I take a bone-building medication. I couldn't tolerate Fosamax, so they want me to take Prolia. I'm worried about it, but my mother had severe osteoporosis, so I'm worried about that too. How can I choose what to do?

Dear Reader: Your worry is well-founded. Osteoporosis is defined as a decrease of bone density greater than 2.5 standard deviations below the bone density of a healthy young adult, and it's more than three times more common in women than men. Women ages 65 to 80 have a 21 percent incidence of osteoporosis; those over 80 have a 35.6 percent incidence.

In addition, women fall more often than men, making bone loss especially dangerous. Three-quarters of all hip fractures occur in women. Not only are such fractures extremely disabling, requiring surgery and hospitalization, but also the overall one-year mortality after a hip fracture is 21.2 percent. Spine fractures are even more common than hip fractures in people with osteoporosis. Although they often go undiagnosed, they can cause debilitating pain.

So, obviously, if there is a way to improve your bone density and decrease your chance of fractures, you should do it.

Taking 500 to 1,000 milligrams of calcium a day and maintaining an adequate blood level of vitamin D are important, but to increase bone density, the first-line drug therapy is a bisphosphonate. These drugs, including Fosamax, increase bone mass and decrease the incidence of fractures. I would assume that you couldn't tolerate Fosamax due to irritation of the esophagus and stomach. If that's the case, you could consider injectable bisphosphonates such as Boniva or Reclast.

That said, all bisphosphonates can have rare, but potentially serious, side effects such as osteonecrosis of the jaw, an increased risk of fractures of the femur, and in the case of Reclast, atrial fibrillation. Also, note that people with kidney failure should not take bisphosphonates.

Prolia, given by injection twice a year, is different. It's a monoclonal antibody that binds specifically to a receptor within bone, inhibiting the normal bone breakdown. Clinical trials showed that, after three years of use, Prolia improved bone density in the spine by 9.2 percent and, after eight years, by 18.4 percent. It improved bone density in the hip by a lesser amount, 4 percent after three years and 8.3 percent after eight years. The drug was also linked to a 68 percent decrease in the rate of spinal fracture and a 40 percent decrease in the rate of hip fractures. In a trial comparing Prolia to Fosamax, those taking Prolia showed a slightly greater improvement in bone density after one year.

That's not to say Prolia is for everyone. Like Fosamax, it can occasionally lead to osteonecrosis of the jaw and atypical fractures. And, for people with kidney disease, it can lead to drops in calcium levels that can cause muscle spasms and abnormal heart rhythms. Finally, because Prolia is injected into the skin and may affect immune function, it may slightly increase the risk of skin infections at the site of the injection.

In summary, if you cannot tolerate Fosamax, you should consider injectable Reclast or Prolia. These medications do have rare, but severe, side effects. However, their benefits appear greater than their risks.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)