Dear Doctor: I have a lot of urinary tract infections. My doctor told me not to drink anything with caffeine, but surely there must be something else I can do. Are there foods I should eat? Not eat?

Dear Reader: First, let me say that you have my sympathies. Urinary tract infections, though they have no outward signs, can be quite painful. Such infections are common, especially in women, who have a short urethra compared to men, meaning bacteria don't have far to travel in order to cause a problem. The majority of bacteria that cause these infections reside in the colon. These bacteria can colonize the area at the exit of a woman's urethra and, from there, move up the urinary tract to cause infections in the upper urethra, bladder or even kidney. These infections usually require antibiotics.

In younger women, sexual intercourse is a substantial risk factor for urinary tract infections, or UTIs, as are spermicide use and having a new sexual partner. Genetics likely play a role as well; daughters born to mothers with a history of UTIs have a greater likelihood of such infections. Further, those who have a UTI before age 15 have a greater chance of recurrent infections later in life.

After menopause, problems with bladder emptying, incontinence and bladder position increase the risk of UTIs. For post-menopausal women, vaginal estrogen can reduce infections, because it improves the natural bacterial flora in the vaginal area and decreases colonization of harmful bacteria. If you develop UTIs after sexual activity, urinating and increasing fluid intake after intercourse may decrease your chances of infection because these actions help flush the bacteria from the urethra.

If these measures -- not proven by any study -- don't reduce intercourse-related UTIs, a dose of antibiotics after intercourse might be warranted. But take care: With increased exposure comes a greater likelihood of bacterial resistance to that antibiotic.

Another alternative is the use of the probiotic Lactobacillus, which helps protect the vaginal area from the bacteria associated with urinary tract infections. It's not as effective as prophylactic antibiotics, but it can decrease infection frequency.

Cranberry extracts have shown an ability in the laboratory to stop bacteria from attaching to urinary tract cells, but studies of cranberry juice and tablets have been mixed. A combined study in 2012 did show a reduced risk of UTIs among women taking cranberry products, but many studies within the larger study showed no benefit.

Studies on caffeine intake and UTIs have been limited. Although caffeine does cause bladder irritability and may worsen the symptoms of urinary frequency and urgency that are seen with a UTI, the polyphenols in tea and coffee may create antibacterial activity within the urine.

A 2003 Finnish study showed that women who had a higher intake of yogurt containing probiotics and berry juice, like cranberry juice, had a lower rate of urinary tract infections. But the data have not been replicated, and the study did not adjust for confounding factors.

Overall, although some people advise women to avoid alcohol, sodas, spicy foods or citrus, I'm afraid there is no good research on specific diets to help stop recurrent UTIs. The best that science can support is cranberry extract tablets; probiotics or yogurt with Lactobacillus; some of the behavioral changes mentioned above; and doses of antibiotics.

(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: First, there was a "superbug bacteria"; now there's a "superbug fungus"? What is this new fungus that I've been reading about? More to the point, how worried should I be?

Dear Reader: Unfortunately, yes, a type of yeast known as Candida auris has been identified as a source of serious illness in a growing number of hospital patients, both in the United States and abroad. Not only is it resistant to existing treatments, it has also eluded efforts by health care personnel to halt its spread.

Yeasts are single-celled microorganisms that are members of the fungus kingdom, which also includes molds and mushrooms. They're everywhere -- in the soil, on vegetation, in waterways and on living creatures, including humans.

Candida yeasts are typically found in the intestinal tract, as well as on mucous membranes and other areas of warm, moist skin. While more than 150 species of Candida have been identified, only about 15 of them are known to cause infections.

For the most part, these tiny organisms live peaceably with their hosts, held in check by the other microbiota that call us humans home. However, factors like stress, taking antibiotics or antifungals, and a weak immune system, to name just a few, can lead to an overgrowth of Candida yeasts. This can result in symptoms such as itching, rash, fatigue or gastrointestinal distress, which vary depending on the area that is infected.

The good news is that most Candida infections are easy to recognize and respond well to treatment. If you've ever had athlete's foot, a vaginal yeast infection, jock itch, diaper rash or oral thrush, then you've had a Candida fungus skin infection. Nail fungus, also caused by Candida, is more difficult to eradicate due to its positioning beneath the nail bed.

The very bad news is that unlike its relatives, Candida auris is emerging as a serious health threat. First identified in 2009 in Japan, the organism has spread globally. As of August 2017, it was responsible for 112 infections in the U.S., more than half of those in 15 different New York City hospitals.

Candida auris is resistant to all three major classes of antifungal drugs. It persists in hospitals and is spread between patients. It's particularly dangerous to people with weak immune systems, such as newborns and the elderly. It can enter a patient's blood stream via wounds, as well as lines or tubes entering the body. Once in the body, it can cause serious invasive infections. Rapid response is crucial, but it is made difficult because Candida auris is difficult to identify.

At first, travel was suspected in the global spread of Candida auris. However, genome sequencing, which is basically a DNA fingerprint, revealed enough differences between regional strains to suggest the yeast has sprung up independently. Needless to say, all aspects of Candida auris are now under intense study.

For all these dire details, you don't have to be alarmed. In most cases, infections occurred in patients who were hospitalized, most of them for several weeks. In the meantime, identifying new treatments and stopping the spread of Candida auris has become an international priority.

(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: Can marijuana use really increase the risk of high blood pressure, as a recent study suggests? I thought marijuana was supposed to make you relax.

Dear Reader: If you'll recall, there was a time when smoking tobacco was similarly touted as a healthy way to relax. Only after years of study and national educational campaigns did the public began to realize the detriments of tobacco. Today, in the desire to legalize marijuana, proponents have focused on its potential health benefits. That doesn't mean it has no negative effects.

In fact, smoking marijuana leads to an increase in heart rate, increased contraction of the heart and a small increase in blood pressure. The 2017 European Journal of Preventive Cardiology study you mentioned attempted to quantify these negative effects.

The data used in the study come from a national survey in 2005 in which people over the age of 20 were asked: "Have you ever used marijuana or hashish?" Participants who answered "yes" were termed "marijuana users." The authors also asked the year that people first used marijuana, from which they calculated total years of use. The authors then looked at mortality data from 1991 to 2011.

In this study, 56.5 percent of the 1,213 eligible participants were qualified as marijuana users. Note that 63 percent of these "users" also had a history of smoking tobacco. The overall death rate of marijuana users was 29.7 percent, while in non-users the rate was 26.2 percent. The authors found that the death rate from high blood pressure was 4.3 percent higher in the users of marijuana, but they didn't find a difference in death rates from heart attacks or strokes.

But let's look at the major problems with this study. First, the definition of "marijuana user" was problematic. People who used marijuana once in their lifetime were quantified as marijuana users. The data didn't differentiate between someone who had used marijuana every day for the last 20 years and someone who used it once in college. Next, the number of participants was relatively small, which affects the conclusiveness of the findings. For example, in this study, cigarette smokers had less risk of dying from a heart attack than did non-smokers. That runs counter to large trials showing the opposite. Lastly, many of the marijuana smokers also smoked cigarettes -- so if the data about cigarette smokers were inaccurate, as the suspect finding suggests, there may be further inaccuracies in the data.

However, the study does highlight that marijuana users had a higher rate of high blood pressure. This was also found in a 2016 study showing a mild elevation of blood pressure in marijuana users. Among people who used marijuana one to six days per month, the systolic blood pressure was elevated by 1.3 points on average, and among those who used 21 to 30 days per month, the systolic blood pressure was elevated by 2.6 points on average.

All these data point to how poorly we understand the health consequences of marijuana use. For example, we simply don't know whether marijuana smoking has the same negative vascular effects as tobacco smoking. With less fear of incarceration over marijuana use, perhaps more people will participate in larger studies to assess marijuana's effect upon the cardiovascular system.

(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.)