Dear Doctor: My husband and I have a running battle with two of our three kids, who have zero interest in anything that isn't on a screen. They're 11 and 13, so rational arguments about their adult health don't work. Just how important is it for kids to get regular exercise?

Dear Reader: We all want the best for our kids, which is often how those smartphones, tablets and video game consoles get into their hands in the first place. But as you rightly observe, children need a certain amount of physical activity in their lives for optimum health. Decades of research have (repeatedly) shown that adults who are physically fit have a decreased risk of developing chronic illnesses and conditions like heart disease, stroke, cardiovascular disease, certain cancers and diabetes. And as we've explored in recent columns, physical fitness also plays a role in improved mood and can help with depression.

Now, thanks to recent reviews of existing research, we're learning that those of us who were physically fit as children are more likely to be fit -- and healthy -- as adults. Yet at the same time, data shows that adolescents today are up to four times as likely to be overweight as they were in 1960. Fewer than half of children between the ages of 9 and 13 engage in organized physical activity outside of school. One-fourth don't take part in any free-time physical activity at all.

Add in the fact that these days, options for regular physical activity in many schools are quite limited, and it's more important than ever for parents to step up and help their kids get moving.

Which brings us to the excellent point you make regarding the challenge of motivating a child, particularly an adolescent, to exercise regularly. The same facts and statistics that are so compelling to us hold little meaning for someone whose next birthday, let alone the strange and distant land of adulthood, seems an eternity away. Meanwhile, the worlds that await within our screens are notoriously seductive. Getting kids engaged in the bland and boring real world isn't easy. But it's during adolescence that we establish what often turn out to be lifelong behaviors, and this includes physical activity. And it's during this crucial time that levels of physical activity tend to decline, a trend that is apt to be even more pronounced among girls.

Current exercise guidelines for children aim for a minimum of 60 minutes of activity per day, with aerobic exercise the gold standard for cardiovascular health. Walking, hiking, skateboarding, running, biking, dance, gymnastics and many team sports can get the heart pumping. Activities to strengthen muscles as well as controlled impact activities like jumping rope, hopscotch or running that help build bone are important.

One of the keys to getting kids off the couch is to model the desired behavior yourselves. Make physical activity a family priority. Family hikes with a picnic at the destination, a basketball hoop in the driveway, games of tag or catch, jumping rope and family bike rides are great ways to get everyone moving. The trick is to start small, build slowly and make it fun. And know that you're in it for the long haul.

(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: Did the surgeon general really just suggest that the general public carry naloxone in case they encounter someone having an opioid overdose? For starters, where would you even get such a thing? And two, how is the average person supposed to know who's overdosing -- and on opioids?

Dear Reader: The opioid epidemic is undoubtedly a national crisis. No other group of drugs has led to such a staggering number of overdose deaths in this country. Of the 63,632 overdose deaths in 2016, two-thirds were related to opioids, with synthetic opioids such as fentanyl and its illegal analogs proving especially dangerous. Overdose deaths from those drugs doubled in 2016 compared to 2015. Further, because these deaths are often concentrated in specific counties, the drugs have led to the destruction of families and even communities. They're widely available, and can be injected, inhaled or taken orally.

Opioids suppress the respiratory system by inhibiting the natural impulse for breathing. In short, with an overdose, people simply stop breathing. As for naloxone (Narcan), it's an opioid receptor antagonist, meaning that it blocks the action of the opioid. The drug typically is given intravenously in emergency situations by medical personnel, quickly reversing the respiratory depression. Even if the drug can't be given by vein, it can be administered by injection into a muscle or under the skin; it can even be placed within the nose via a spray. Although naloxone is a lifesaver, it must be quickly given to prevent death.

That fact prompted the surgeon general to state that naloxone should be carried by members of the general public in the event they encounter an opioid overdose. Already, naloxone -- in injectable or spray form -- can be obtained without a prescription in 46 states. (The other four require a doctor's order.) Because pharmacies carry the medication, one could simply obtain the medication from a pharmacist, who could then teach how to administer it.

As the surgeon general pointed out, naloxone would be beneficial for family members and friends of people struggling with addiction. The need is especially great in areas far from the medical personnel generally needed to provide the drug in a timely fashion.

As for when it should be administered, that would be when a friend or family member -- whom you know to be taking a prescribed or illegal opioid -- becomes non-responsive and stops breathing. First, you would perform CPR, complete with rescue breathing, and if you get no response after 30 seconds, you would give naloxone. The drug should work quickly, but if it doesn't, you would administer it again in two to three minutes.

One note of caution: The naloxone may precipitate a severe withdrawal from the drug, but opioids should not be given to combat this. Instead, further medical attention would be required.

But increasing the availability of naloxone won't eliminate all deaths from opioid overdoses. For starters, we could face a shortage of the medication and will likely need greater production of naloxone. And, of course, we need greater access to resources that can help us both treat and prevent opioid addiction.

(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: Just how effective is exercise against depression? I read that stopping exercise worsens depression in as little as three days, so that seems pretty powerful.

Dear Reader: After decades of research into the subject, it's safe to say there's a clear connection between exercise and a sense of well-being. Studies have shown that regular exercise improves mood and can have a positive effect on symptoms of depression. Considering that up to 10 percent of people in the United States are now dealing with depression, the mental health benefits of exercise are very good news. Now, findings from researchers at the University of Adelaide in Australia support what many part-time exercisers may have already intuited -- that when you stop being active, those mental health benefits fade away.

The scientists noted that while numerous studies have looked into the positive effects of an ongoing exercise program, there was a lack of information about what happens when people stop exercising. To fill in that gap, they reviewed existing data from nine studies in which a total of 152 adults with symptoms of depression first undertook and then ceased an ongoing exercise program. Though the specifics of the activities varied, participants had been exercising for at least 30 minutes three times per week, for a period of three months.

When they crunched the data, the authors found that in some participants, depressive symptoms reappeared in as little as three days after stopping their exercise regimens. Other participants reported a return of symptoms after one and two weeks. In all of the studies, the effect was more pronounced among the female participants than in the men. As with all studies that examine existing data, cause-and-effect conclusions can't be made. But the apparent connection between the cessation of exercise and a fairly quick return of symptoms of depression is worth further study.

As for exercise itself, any increase over a sedentary lifestyle can yield positive results. When researchers followed 22,500 people in Norway over the course of nine to 12 years, they found that those who had engaged in regular exercise, some of them for as little as one hour per week, had a reduced risk of developing symptoms of depression. Even more surprising, it didn't matter how intense that activity was. Although a one-hour walk in the park wouldn't deliver the endorphin high of a brisk run, it still yielded mental health benefits. Whether it was the social aspect of being among people, the self-discipline required to get up and out of the house, or the sense of structure conferred by a regular routine, researchers found it added up to an improved sense of well-being.

The takeaway here is to do something, and to do it regularly. We think that you'll have the best shot at success if you do something you truly enjoy. Believe it or not, there are studies that highlight the mental health (and physical) benefits of jumping on a trampoline. Resistance training -- that's weight lifting -- has been shown to improve mood as well as muscle tone. Perhaps yoga or tai chi, Pilates or dance classes are more to your taste. The important thing is to get started.

(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.)