Dear Doctor: Out of the blue, my new primary care doctor asked me if I owned a gun. Was it appropriate, or even legal, for her to ask that?

Dear Reader: I can understand why you were surprised. Doctors generally try to avoid wading into political discussions, which, as we know, the topic of guns has become. Lately, though, many have been reassessing that arms-length stance and focusing on guns as a public health issue. That's because, as doctors, our concern is preventing illness and injury. We freely speak out against the abuse of alcohol, tobacco and sugar -- all of which are legal -- because we would like to prevent alcohol addiction, smoking and an over-consumption of sugar. Without advocating legal action against these substances, we ask probing questions of our patients and, we hope, give good advice to prevent injury.

The big issue with guns is violence. Put simply, guns are an effective way to injure and kill people -- or, as we think of them, our patients. How many patients? Let me put it this way: In 2015, 36,252 people died of gunshot wounds in the United States. More than 80,000 others are injured each year.

The majority of deaths by firearms -- two-thirds -- are due to suicide. Simply having a gun in the house increases the rate of suicide by gun. This may seem obvious, but having a gun in the house also increases the overall rate of suicide, especially among men. The U.S. rate of suicide by firearm is about 11 times that of other industrialized countries.

Health care professionals particularly worry about depressed patients with access to guns, fearing that those who believe they would be better off dead will more easily act on that belief. Because guns are such an easy, impulsive way to commit suicide, knowing that a gun is in the house can help us more effectively counsel and guide patients.

This is especially useful information when we're counseling military veterans, who have nearly twice the rate of suicide as civilians and who are often comfortable around guns, and when we're assessing overall child and adolescent safety. For adolescents, the rate of suicide is two to three times greater when there is a gun in the house. Further, because of adolescents' poor impulse control, we also worry that they'll use the gun on other people.

Of course, guns in the house are often used for protection. But people with access to a gun have twice the likelihood of being a victim of homicide.

All these statistics lead us to this: Physicians increasingly feel a moral obligation to assess whether a gun is kept in the house and, if so, whether they're kept unloaded and locked in a secure place separate from the ammunition.

It's possible that your physician saw a risk factor -- a history of depression or a potential threat to children -- and is doing her due diligence. It's also possible that she's responding to recent calls from leading physicians to ask all patients about access to weapons within the home.

Regardless, her question was legal -- and meant to protect both you and your loved ones.

(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 read that not getting enough sleep can increase my risk of Alzheimer's disease. I've had occasional trouble sleeping most of my life, and it seems to be getting worse as I get older. How worried should I be?

Dear Reader: Just like food, water and the air we breathe, getting enough high-quality sleep is vital to our well-being. As anyone who has pulled an all-nighter can attest, lack of sleep can impair reasoning and problem-solving, interfere with learning, and even lead to accidents or injury. Chronic sleep deficit, meanwhile, has been linked to health issues as serious as diabetes, obesity, cancer and heart disease.

Ongoing research continues to find a correlation between sleep deficit and various types of dementia, including Alzheimer's disease. In one of the more recent studies, participants who reported sleep problems like insomnia, poor sleep quality and daytime sleepiness had a measurable increase in amyloid plaques in their spinal fluid. These sticky proteins are considered to be indicators of Alzheimer's disease.

Just how does the sleep-wake cycle affect these Alzheimer's markers? Researchers at the University of Rochester Medical Center believe they have discovered a significant piece of the puzzle. In studies published in 2012 and 2013, they revealed the existence of a cleansing system in the brains of mice, which removes waste products at a rapid pace.

They dubbed it the "glymphatic system" because it mirrors the waste-clearing function of the body's lymphatic system, but is managed by the glial cells in the brain. Unlike cerebrospinal fluid, which plays a crucial role by circulating nutrients to the brain and clearing away debris, the glymphatic system is not passive. It's swift, efficient and reaches all corners of the brain.

What's particularly intriguing is that the glymphatic system is active during deep sleep. Researchers found that during these stages of sleep, the cellular structure of the brain shifts. The spaces between the cells open, allowing the toxins that built up while we were awake to be quickly removed. The glial cells control the flow by shrinking during deep sleep to allow for rapid movement, then swelling again during REM sleep and at waking, all but shutting the system down.

The takeaway is that a good night's sleep, which includes adequate deep sleep, literally clears out the brain. When we skimp or get poor-quality sleep that doesn't include adequate deep sleep stages, we impair the brain's ability to cleanse itself of potentially damaging waste materials.

Thus far, the glymphatic system has been confirmed only in mice. However, the mouse brain is surprisingly similar to the human brain, which is why it is used for study. As scientists build on this research, further discoveries will be made. But at the very least, we are reminded how important sleep is to good health and well-being.

As for your question about whether you should worry, we want to reassure you. Just because a symptom and a disease can be connected, it doesn't mean that they must be. The nature of research like this is to identify patterns for future study. The fact that you have experienced sleep problems does not mean that an Alzheimer's diagnosis is inevitable.

(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: My granddaughter plays soccer, and I've long been worried about the risk of concussion. Now I read that they last longer in girls. Why?

Dear Reader: This is a worry to which I can most definitely relate. My daughter is an aggressive soccer player and sometimes attempts to head balls during games. While I want her to do well in the sport, I worry about her risk of concussions. These head injuries can occur from a direct blow, such as when the head hits a soccer ball, or from a hit to the body in which the head is jarred.

One recent study assessed the effects on middle school and high school athletes -- patients of a sports medicine practice in southern New Jersey -- who had sustained a concussion in the years 2011 through 2013. The physician researchers assessed whether the athletes had a history of headaches, learning disabilities or mental illness, and whether they had suffered a loss of consciousness or problems with memory after the concussion. They also measured the athletes' symptom score (impact score) to assess the severity of the concussion and evaluated the length of days the athletes had symptoms after the head injury.

On the initial impact score, the 102 female athletes had a slightly higher score (17) than their 110 male counterparts (14). The male athletes had the greatest number of concussions from football, while the female athletes had the greatest proportion from soccer.

What was most striking about this study was the length of time it took for the athletes to recover to the baseline status. In the males, the median time was 11 days, while for females it was 28 days.

Another recent study, involving 2,004 high school students, compiled concussion data from 147 high schools from 26 states between 2011 and 2014. Again, the predominant causes among the male and female students were football and soccer, respectively. Overall, male athletes were more likely than female athletes to recover within one week; female athletes were more likely to take longer than 19 days. Player-to-player contact was the most common mechanism of injury for all sports. But, in soccer specifically, while 70 percent of male concussions were from player-to-player contact, only 40.6 percent of female concussions were from such contact. For females, 46 percent were from head-to-ball to contact.

A 2010 study with 215 males and females with concussions did not show any gender differences among athletes who continued to have symptoms after 90 days, but it did show that among the males, 16.3 percent recovered in one week, compared to 7.4 percent of the women.

It has been hypothesized that concussions last longer in females because they generally have decreased musculature in the neck compared to males. This may create less ability to absorb shock, leading to a greater acceleration of the brain within the skull. Other contributors may be the higher rates of headaches, depression and anxiety in adolescent females compared to males, which may contribute to a prolonged recovery from a concussion.

I wouldn't discourage your granddaughter, nor my own daughter, from playing soccer -- it's a fun sport. But it wouldn't be a bad idea for us to get them a tennis racquet for their next birthday.

(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.)