Dear Doctor: I recently read about a sugar additive being linked to the rise of a killer bug. What is this additive, how do I avoid it, and how serious is the threat?

Dear Reader: Clostridium difficile, or C. diff, is a bacterium that can cause severe intestinal infections, leading to severe diarrhea, possible hospitalizations and even death, especially in people over the age of 65. Antibiotic use is often the precipitating factor in C. diff infections because the drugs kill off the normal bacterial populations in the colon and allow for C. diff to multiply and release toxins, triggering inflammation and diarrhea. Rates of C. diff infection are increasing in this country, with nearly 500,000 people per year affected and 15,000 deaths. Use and overuse of antibiotics are blamed for this increase. But a recent study in the journal Nature may point to another factor.

First, note that C. diff has different subtypes, or ribotypes, with two strains in particular -- RT027 and RT078 -- associated with large outbreaks of disease. These outbreaks have been common since the year 2000. The year is important because that's when the sugar trehalose became available for mass production and began to be readily placed in foods and drinks. Of course, many notable things occurred in the year 2000, so let's explore how a sugar product could specifically be blamed for an increase in the risk of C. diff outbreaks.

Trehalose is a naturally occurring sugar produced by plants, fungi, bacteria and insects that helps organisms retain water and prevents cellular damage when there is no water. It's about 45 percent as sweet as sucrose (or table sugar), but researchers for years lacked a cost-effective way to extract it. However, in 2000, a new enzymatic extraction method led to a cheap way to mass-produce trehalose. Subsequently, many food products and drinks were produced with this sugar as an ingredient.

The study you are referencing looked at how the C. diff ribotypes RT027 and RT078 respond to trehalose. For starters, RT027 will grow five times greater than other ribotypes of C. diff when trehalose is a food source. Also, RT027 needs lower concentrations of trehalose to turn on enzymes that metabolize the sugar. Mice infected with the RT027 type were three times as likely to die when given a solution that mimicked human intake of trehalose compared with those given water. The ribotype RT078 also shows an increased ability to metabolize trehalose.

Further, the small intestine doesn't absorb trehalose as well as it does sucrose. This leads to more trehalose ending up in the large intestine, which is where C. diff causes its damage. Thus, if a patient has an RT027 or RT078 strain of C. diff and trehalose is present in the large intestine, the bacteria can readily use trehalose to survive and multiply. These bacteria will also have a competitive advantage over other bacteria in the colon that cannot utilize trehalose.

It's one of those quirks of nature that a bacterium can use a naturally occurring substance to its benefit -- and our detriment. I would look at food labels and evaluate whether your diet is high in this sugar. If so, you might want to make adjustments. The data are concerning.

(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 26 years old and have been diagnosed with lymphedema in all four limbs. I'm 5 feet 8 inches and weigh 193 pounds. I work out for an hour every morning and am physically active. What else can I do to help my lymphedema?

Dear Reader: Lymphedema is the swelling that occurs in the arms, legs or other parts of the body when the lymphatic system is not functioning properly. It's most common in cancer patients who have had lymph nodes either removed or damaged during surgery or treatment. Swelling caused by injury to the lymphatic system is known as secondary lymphedema. When the swelling occurs independent of surgery or other damage, as in your case, the condition is known as primary lymphedema.

The lymphatic system, which is part of the immune system, is a circulatory system that includes all the tissues and organs that produce, store and carry white blood cells. A crucial part of this system is the network of lymphatic vessels that serve tissues throughout the body. Similar to capillaries, these are thin-walled tubes that drain fluid from the tissues and carry it to the lymph nodes. Unlike capillaries, however, which have the force of the heartbeat to move the blood within them, the lymphatic system is largely dependent on muscle movement to keep things flowing.

The type of lymphedema you have is quite rare. It's an inherited condition in which the lymph vessels have not formed properly. As a result, the protein-rich lymph collects in the layers of soft tissue beneath the skin. This causes swelling in one or both legs, one or both arms, and can also affect the face and trunk.

When you have lymphedema, it's important to seek professional care. The condition puts you at higher risk of developing infections of the skin and underlying tissues, which in turn can lead to abscesses, ulcers and tissue damage. Something as simple as a scratch or cut or insect bite can lead to serious infection.

There is no known cure for lymphedema, and no FDA-approved medication. However, complete decongestive therapy, also known as CDT, is an important tool in controlling the condition. In CDT, a lymphedema therapist leads you through a comprehensive program that includes manual lymphatic drainage, bandaging, the use of compression garments and self-care.

Manual lymphatic drainage, performed by the therapist, uses a feather-light touch to move lymph from the tissues and direct it back into the lymphatic vessels. Compression garments, which are made from flexible fabrics, keep a steady pressure on the affected limb and keep lymph moving.

Self-care includes protecting your limbs from cuts, scrapes, insect bites, overuse and extreme temperatures. Maintaining a healthy body weight is important in managing lymphedema. So is regular exercise, which you've already incorporated into your life. Be sure to run the specifics of your routine by your lymphedema therapist.

Managing lymphedema takes sustained effort and attention. That's why, once again, we're going to urge you to work with specialists in the field. For help finding a lymphedema therapist, visit the National Lymphedema Network at lymphnet.org.

(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: If vitamin D and calcium don't reduce the risk of bone fractures in older adults, as I recently read, is there any point in taking them?

Dear Reader: For years, the medical community has been touting calcium and vitamin D to prevent fractures; I've been guilty of this practice as well. Although some studies suggested that calcium and vitamin D could help prevent osteoporosis, the degree of improvement was never overwhelming. Still, we held fast to our medical dogma. Now, as you mention, a study has shown the need to look at the data without bias in order to provide more nuanced counsel to our patients.

The research, recently published in the Journal of the American Medical Association (JAMA), reviewed 33 studies -- with a total of 51,145 participants -- assessing the risk of fractures in people taking either calcium alone, vitamin D alone or calcium with vitamin D.

The calcium-only studies included various types of the mineral: calcium citrate, carbonate, malate and gluconate. The seven studies assessing the impact on hip fractures showed no improvement with the use of calcium. In fact, researchers found a 53 percent increase in the risk of hip fractures among people taking calcium. The findings on spinal fractures were more positive. Nine studies assessed that connection, finding a 17 percent decrease in risk with calcium use. Seven studies assessed total fracture rate, finding a 12 percent decrease in risk, but the rate was not considered statistically significant.

The studies that assessed the specific impact of vitamin D similarly failed to produce positive results. In the nine studies of vitamin D use and hip fracture, researchers found a 21 percent increase in the risk of fracture among those taking vitamin D. The studies assessing the impact on spinal fracture and total fractures simply found no benefit.

The studies assessing the impact of calcium combined with vitamin D yielded only marginally better results. Although the seven studies looking at the impact on hip fractures found no reduction in risk, the three studies looking only at spinal fractures did show a 37 percent reduction in risk. The studies that looked at total fracture rate showed a non-significant 10 percent reduction in risk.

The 33 trials varied in length from four months up to seven years. Of note, many studies conducted for longer periods were more likely to show a reduction in the risk of spinal fractures with the use of calcium or vitamin D, which may be because calcium and vitamin D are slow to improve bone density.

The JAMA study did not specifically look at people with osteoporosis. For them, calcium has been shown effective in maintaining bone density. A 1992 study of female nursing home residents (who have a higher likelihood of osteoporosis) found that calcium and vitamin D decreased the rate of hip fracture by 43 percent and the overall fracture rate by 32 percent.

So, if you have osteoporosis, I would recommend calcium and vitamin D. If you're a healthy person without osteoporosis, calcium and vitamin D may produce a slight decrease in the risk of spinal fracture. Overall, however, there seems to be little benefit to this supplementation.

(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.)