Dear Doctor: A friend of mine was diagnosed with methicillin-resistant Staphylococcus aureus, or MRSA. How does a person even contract such a disease -- and what does it do to you?

Dear Reader: Methicillin-resistant Staphylococcus aureus, or MRSA, is a bacterium that is resistant to methicillin and other penicillin-related antibiotics. These drugs normally bind to a specific protein on the bacterium, leaving it unable to produce a cell wall. MRSA, however, has a gene that produces a protein that doesn't bind to methicillin or its cousins, making it harder to defeat.

People can acquire MRSA in two ways. One is through a health care setting, either in a hospital, nursing facility, surgical center or dialysis facility. Infections acquired in those settings can manifest between 48 hours and a year after exposure. They're more likely if a patient is over-prescribed penicillin-related antibiotics (making them more resistant to the drugs); is in a room or setting next to somebody with a MRSA infection; or is on dialysis. Although hospitals take painstaking measures to ensure a sterile environment free from harmful bacteria, MRSA forms a biofilm that attaches to inert objects, such as catheters and breathing tubes. From there, it can more easily invade the body. It can also attach to the hands of health care workers and many surfaces, and, from there, make its way to patients.

The second way to acquire MRSA is within the community. Outbreaks have been noted among sports teams, in childcare centers, among military personnel and in prison populations. Even animals can carry the bacterium and pass it on to a human host. Such cases are predominately skin infections, including cellulitis, folliculitis and abscesses. The bacterium can also be passed among household members. A 2012 study of 148 MRSA-infected patients found that 19 percent of their household contacts had colonized the bacteria.

In humans, MRSA colonizes within the nose, within the throat and upon the skin. That doesn't mean it causes infections, but rather that it's lurking there, ready to cause an infection should a person's immunity be compromised. From there, it can also spread to others, who may be more susceptible. A 2010 study of hospitalized patients found that 7 percent had colonized MRSA. In two 2008 studies of health care workers in the emergency room, between 4 and 15 percent had colonized MRSA within their nose.

MRSA not only causes skin infections, but can lead to pneumonia, infections of the bone and within joints, infections of the heart valves, and urinary tract infections. The infections can seep into the blood and pass to multiple organs. In 2005, MRSA led to an estimated 18,500 deaths in the United States.

All is not lost, however. The spread of MRSA can be controlled in hospitals and outpatient clinics if health care workers wash their hands after seeing patients, and if they use gloves and masks when seeing patients with MRSA. In households with a MRSA-infected family member, residents should be extremely diligent about hand-washing. The antiseptic chlorhexidine is especially effective at removing the bacteria from the skin. Further, those diagnosed with colonized MRSA in the nose can take the nasal antibiotic ointment Mupirocin.

Also, I'll say it again: Limiting the use of antibiotics will decrease the chance of bacterial resistance to them -- and decrease the chance of MRSA.

(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 recently read about a woman who died from a protein overdose. Is it really possible to have too much protein? How much are we supposed to be eating?

Dear Reader: We remember the news story you're referring to as it caused quite a stir. A bodybuilder from Australia, who had put herself on a high-protein diet in order to prepare for a competition, was found unconscious in her home. She passed away two days later.

Although the cause of death was listed as "intake of bodybuilding supplements," the story is actually more complicated. An autopsy revealed that the woman had a rare genetic condition that made it impossible for her body to efficiently digest protein. Known as urea cycle disorder, it's a deficiency in one of the enzymes in the liver that scrubs the blood of nitrogen, a waste product of protein metabolism.

When the urea cycle is functioning properly, nitrogen is removed from the blood, converted to urea, and transferred to the urine for elimination. But in individuals with urea cycle disorder, the nitrogen accumulates in the tissues in the form of ammonia, which is extremely toxic. Ammonia is carried through the blood to the brain, where irreparable damage can occur.

Though there is no cure at this time, the condition can be managed through diet and various medications and supplements. In the case of the bodybuilder, her disorder was undiagnosed. It had been mild enough that, when she ate normally, she didn't have any serious problems. However, when she upped her protein intake to prepare for the competition, she inadvertently pushed her body beyond the limits of what it could manage. As a result, the ammonia in her blood reached fatal levels.

When it comes to recommendations on how much protein we should eat, there is a bit of debate. According the Recommended Dietary Allowance (RDA) in the United States, it's 0.8 gram of protein for every kilogram of weight. And for us in the non-metric U.S., that's 0.36 grams of protein per pound of weight. Age and activity level play a part as well. The U.S. Department of Agriculture has a nifty online calculator: www.nal.usda.gov/fnic/interactiveDRI/.

Most of us who eat a balanced diet will have no problem meeting the RDA for protein. For very active individuals, elite athletes, or those working to lose weight or build muscle, more protein may be advisable. On the other side of the spectrum, people living with kidney disease must take care not to eat too much protein. A high-protein diet can impair kidney function due to the increase in waste products from protein metabolism.

Some nutrition researchers believe the RDA for protein should be increased to slightly more than the current recommendations. Until that debate gets resolved, the RDA is our best guide. For anyone who wants to increase his or her protein intake, we recommend consulting with a nutritionist or sports medicine specialist for information and guidance.

(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: Calcium is frequently recommended to reduce the risk of bone fractures in the elderly, but I've read that calcium builds in the arteries and heart. So what choice do women have -- die of a hip fracture or die of a heart attack? Personally, I don't know which would be better.

Dear Reader: You highlight an interesting issue. There is no doubt that calcium is beneficial for bones, with supplementation improving bone density and -- at 500 to 1,200 milligrams per day -- leading to a 9 to 19 percent decrease in the rate of hip fractures. But it's true that supplements may have risks as well.

First, for women over 50, supplementation with 1,000 mg of calcium and 400 IU of vitamin D leads to a 17 percent increased risk of kidney stones. Second, calcium supplementation for people with kidney dysfunction or those on dialysis causes increased calcification of blood vessels and a greater risk of heart attacks and strokes.

A 2008 study of 1,471 postmenopausal women in New Zealand compared the effects of 1,000 mg of calcium citrate to those of a placebo. In five years of follow-up, women who took the calcium had an improvement in the ratio of their good to bad cholesterol (HDL/LDL). However, after 2 1/2 years, the group that took the calcium started to show an increased risk of heart attacks; after five years, they had a 49 percent increased risk.

Then there was a 2010 British Medical Journal study that combined data from 11 studies in which women took elemental calcium supplements of 500 mg or more. The studies, which evaluated fracture risk and bone density, weren't intended to assess heart attack and stroke risk, but researchers did gather data on the conditions. In total, the group that took calcium had a 27 percent increased risk of heart attacks and a 12 percent higher risk (not considered statistically significant) of strokes.

In 2011, the same authors tackled data from the Women's Health Initiative (WHI) study in which 36,282 women took 1,000 mg of calcium and 400 IU of vitamin D or a placebo for seven years. The initial study did not reveal an increase in heart attacks among women taking calcium supplements, but as it turned out, 54 percent were taking additional calcium beyond the supplements that were part of the trial. Noting this, the authors of the study compared their data with data from the 46 percent who were not taking additional calcium. They found that the group taking the 1,000 mg of calcium had a 16 percent increase in the rate of heart attacks.

Other grouped studies (using the initial data of the WHI study) have not shown this degree of risk with calcium supplementation.

Confusing, isn't it? Here's the take-home message: If you're otherwise healthy, taking up to 1,000 mg of calcium supplements may be safe. But if you have risk factors for a heart attack or stroke, such as a history of smoking, diabetes, kidney dysfunction or a significant family history of heart disease, I would avoid large doses of calcium and would, in fact, limit calcium supplement intake to no more than 500 mg per day. It's all about balancing bone health with overall health.

(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.)