Dear Doctor: Could energy drinks really lead to stimulant use? How can that be? No one’s ever linked coffee or cola consumption to an increased risk of drug abuse. This sounds like some kind of urban legend.

Dear Reader: Considering the centuries-long history of coffee drinking, and the estimated 2.5 billion (!) cups of the stuff consumed each day worldwide, your skepticism is understandable. However, a 2009 study by researchers at the University of Maryland indeed suggested a link between the sustained use of energy drinks by young adults and the chance of future abuse of certain types of drugs.

The study began with 1,060 first-year college students with an average age of 18. Over the course of the following three years, the students completed three annual interviews regarding their use of energy drinks, any other sources of caffeine, and alcohol and tobacco use. The students also reported the use of prescription drugs, and any illegal drugs. In a series of post-college interviews, which took place when the participants were between the ages of 21 and 25, the researchers assessed their drug use.

Over the course of the first three years of the study, about half of the students either diminished or stopped using energy drinks. The other half continued to consume them in the same large quantities. When they followed up several years later, researchers found that students who continued robust energy drink use went on to have a markedly higher risk of using cocaine or illicit stimulants after the age of 25 than did the group of occasional or nonusers. The high-use group was also found to have an increased risk of alcohol abuse.

Whether the energy drinks themselves set the stage for the future drug abuse, or whether the individuals who were naturally susceptible to drug or alcohol abuse were also drawn to the effects of the energy drinks, is not known. However, the researchers concluded that the implied connection between sustained energy drink usage among young adults and the potential for future illicit stimulant use deserves further study. With an estimated one-third of teens between the ages of 12 and 17 now regularly downing several energy drinks per day, we heartily agree.

Addiction aside, ongoing studies continue to identify a range of health risks associated with energy drinks. These include increased blood pressure, heart arrhythmias, sleep disturbance, damage to the heart and blood vessels, kidney damage and weight gain. This last may seem counterintuitive for a product engineered to rev you up, but many varieties of energy drinks contain excessive amounts of sugar, up to 2 or more tablespoons per 8-ounce can. That means just one energy drink will put you over the recommended allotment of sugar for the day.

In addition to caffeine and sugar, energy drinks contain a range of herbs, enzymes, vitamins and other additives. And because the products are not regulated, you can’t always know exactly what you’re ingesting. Bottom line -- research repeatedly shows that energy drinks can have serious health effects, particularly in children, teenagers and young adults.

(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.)

Hello again, dear readers, and welcome to our monthly column devoted to your thoughts, notes and suggestions. We’re deep into spring, so here’s our annual reminder to be on high alert for ticks. Dress defensively, use repellents and do thorough and regular tick checks. Always seek medical care if a tick bite is followed by a rash, fever or other flulike symptoms. Be sure to also protect any four-footed companions with access to the outdoors. And now, to the inbox.

-- Many of you wrote in response to a column about the health benefits of nuts, asking if roasted and salted nuts are OK. Although roasting doesn’t affect protein, fiber or carbohydrate content, it may chemically alter the healthy fats that nuts contain. Roasting can also cause the formation of acrylamide, a compound that has been studied as a potential carcinogen. Roasted nuts have less acrylamide than potato chips or french fries, and the American Cancer Society says the effect on cancer risk in humans remains unclear. Regarding salted nuts, the main caution is to include the added sodium in calculating your total daily intake. This shouldn’t exceed 2,300 milligrams, and is hopefully closer to the American Heart Association’s goal of 1,500 milligrams per day.

-- Regarding a column about sexually transmitted diseases, a reader asked whether washing or douching after sex will protect against sexually transmitted diseases. The answer to both of those is NO. The best protection against STDs is the correct and consistent use of latex condoms, which can prevent transmission of both bacterial and viral STDs.

Although topical microbicides, which are substances like gels, films or suppositories, can kill or neutralize viruses and bacteria, it is recommended they be used along with condoms. Since some STDs can be transmitted via oral sex, it’s important to have a frank conversation about sexual history and potential health risks with your partner before sex.

-- We heard from a lot of parents in response to the column about the potential problems caused by the heavy school backpacks our kids are now toting. One reader wishes we had gone into more detail about how to lighten the load.

“This is a good time to teach children how to plan and decide what to keep in their backpack all the time versus what they need at certain periods of the day,” she wrote. “Many keep everything just because they might need it. Teaching them planning, time management and simple solutions like rotating books and binders during their day, or sharing binders for several morning or afternoon classes, can lighten the load.”

-- When we write about dogs, we get a ton of mail. In response to a recent column about a grandfather’s plans to adopt a dog, a reader from Oklahoma pointed out that pets aren’t for everyone: “If the person has balance problems or vision problems, there could be a high likelihood of tripping over the pet,” he wrote. “That could result in some serious injury.”

Thank you, as always, for your interest and engagement with this column. We love hearing from you and look forward to your letters.

(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 second husband and I have tried to get pregnant for over a year now, but we have had no luck. Should we be worried about infertility? I’m the mother of a 2-year-old girl and a 4-year-old boy, so the problem probably isn’t with me. What causes that in a man?

Dear Reader: When a woman and man have not achieved pregnancy after a year of regular unprotected sex, they meet the clinical definition of infertility.

You and your husband may feel as though you’re alone in this, but studies suggest that up to 15% of couples are unable to conceive in the first year of trying. About one-third of the time, infertility is due to issues with the man; one-third of the time, it’s issues with the woman; and in the remaining cases, the problem lies in an often-complex mix of issues with both partners. In some cases, the cause of infertility cannot be identified.

For men, the most common causes of infertility are tied to problems with sperm production and sperm motility. These can arise as a result of health problems like diabetes; previous infections such as the mumps or HIV; hormonal problems, including low testosterone; various genetic issues; sexually transmitted diseases; autoimmune disorders; and even lifestyle factors such as smoking, drinking, illicit drug use or steroid use. Some men have blockages in their reproductive systems that can range from partial to total, and that can affect the sperm count. These can be present from birth, or they can develop as the result of physical trauma.

Swollen veins in the scrotum, known as varicoceles, can have a negative effect on sperm growth. These are present in up to 40% of men with infertility problems. A condition known as retrograde ejaculation, which prevents sperm from exiting via the penis and sends it to the bladder instead, can result in infertility in men with normal sperm counts.

Certain medications can change sperm production, function and delivery, including those used to treat depression, infection, high blood pressure and arthritis. Chemotherapy and radiation treatments can also affect male fertility. The causes of male infertility are numerous and varied -- our list is nowhere near complete -- and addressing the issue requires medical assistance.

Diagnosis begins with a physical exam, which will include a detailed medical history. Your husband will be asked about chronic health conditions, past health problems or injuries, prior surgeries and environmental or lifestyle factors. In addition to those already mentioned, they can include obesity, stress, age and diet.

Knowing one’s family history helps to identify inherited conditions. Your husband will also be asked for a semen sample to assess sperm count, structure, motility and concentration. If the semen analysis finds no problems with the sperm, then further testing is needed. This can include hormone tests, scans of the testicles and scrotum to visualize possible blockages, and post-ejaculation urinalysis to look for sperm in the urine. Treatment depends on the results of the tests. Hormone therapy helps to address low testosterone. Surgery can often successfully remove blockages.

Unfortunately, diagnosing male infertility is challenging and a definitive answer is not always found.

(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.)