Dear Doctor: My Type A husband, who naturally falls asleep for about 25 minutes on weekend afternoons, complains that he's wasting time when he does so. How do I explain to him the benefits of napping?

Dear Reader: Millions of people throughout the world take a daily nap. In many cultures the afternoon sleep break is built right into everyday life. Businesses close shop and everyone heads home for lunch and a bit of shut-eye.

Here in the goal-oriented United States, though, napping carries a bit of stigma. It sounds as though your husband has internalized that feeling, which is too bad because you're correct -- a daytime nap is often a good thing.

Studies show that napping does more than just reduce fatigue. It can elevate your mood, improve productivity and make it easier for you to learn and retain new information.

However -- and this is where things get a bit tricky -- not all naps are equally beneficial. It turns out that what time you nap and how long that nap lasts make a difference.

A nap as brief as 10 minutes and up to 30 minutes can leave you feeling energized. Sleep much longer than half an hour and chances increase that you'll wake in a mental fog. The reason for all this is that sleep is quite complex. Not only are there several different stages of sleep, they occur in distinct cycles.

When you first drift off, you move from light sleep, from which you can awaken easily, into stages of ever-deeper sleep. Your brain waves and even your brain chemistry change. It becomes progressively more difficult to awaken. People in the stage known as "deep sleep" show no muscle or eye movement.

The other stage of sleep is known as REM sleep, which is short for "rapid eye movement." This is the cycle during which you dream, and in which the brain registers significant electrical and chemical activity. Fall short on REM sleep and it's quite possible you'll wind up feeling cranky or irritable.

Which leads us back to the question of optimal napping.

First -- what time to close your eyes. Sleep experts agree that mid-afternoon is optimal. Your body clock is naturally primed for a break, and it's far enough away from bedtime so as to not interfere with your night sleep.

Next, the reason why a brief nap feels best.

It takes about 90 minutes for your body (and brain) to go through a complete sleep cycle. Sleep too little and you've barely grazed the surface of light sleep. Sleep too long and you're swimming up from the groggy depths of deep sleep. Aim for 20 to 30 minutes, which puts you into the earliest stages of REM sleep and lets you wake up easily, feeling refreshed.

For the best naps, choose a location that's dark and quiet. Lying down results in better sleep than sitting or reclining. Setting an alarm will let you relax into your nap and assure that you'll wake up before deep sleep takes hold.

When you wake up, take a moment to stretch and take a few deep breaths. And enjoy. A good nap is one of life's real pleasures.

(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: What are the possible health risks from artificial sweeteners? What are they, and how do we know if they're safe?

Dear Reader: It's been well over a century since a scientist at Johns Hopkins University who was fiddling around with the byproducts of coal tar (that's right, coal tar) accidentally discovered saccharine. It caused a sensation, and a decade later saccharine, which scientists estimate to be between 200 and 700 times sweeter than table sugar, could be found in many sodas and some canned foods.

Since then, as you noted, a host of new artificial sweeteners have hit the market. Some, like cyclamates, which were linked to bladder cancer in lab rats, were subsequently withdrawn. Others, despite undergoing rigorous study before getting approval from the Food and Drug Administration, continue to be the focus of skepticism and scrutiny.

At this time, six artificial sweeteners -- also known as "non-nutritive" and "high-intensity" sweeteners -- have received FDA approval. These are saccharine, sucralose, aspartame, acesulfame potassium, neotame and advantame. Each is at least several hundred times sweeter than sugar. Advantame is said to be 20,000 times sweeter than sugar. It, along with all the other FDA-approved artificial sweeteners except saccharine and aspartame, is heat-stable. That means these can be used in baking.

Stevia, a sweetener made from the leaf extract of a plant native to parts of South America, gets a Generally Recognized as Safe (GRAS) nod from the FDA. That means it doesn't need formal approval for use. However, the stevia leaf itself, as well as crude stevia extracts, are not cleared for use at this time.

Artificial sweeteners have undergone years of testing in order to get approval from the FDA, which means they are considered safe for human consumption. Sucralose, for instance, was studied for 20 years before getting FDA approval. However, as we mentioned before and as your letter illustrates, not everyone feels comfortable with these products.

Some subsequent studies linked various artificial sweeteners to health problems in the rats and mice used in experiments. But when this research underwent scrutiny by groups such as the National Cancer Institute, it was determined that inconsistencies in the data prevented clear conclusions from being drawn.

A fascinating group of studies has suggested that, contrary to their no-calorie logic, artificial sweeteners don't help with weight loss. In fact, the promise of sweetness without the caloric payoff actually backfires. It sets off a chemical reaction in the brain that results in increased craving for sweets. And because seemingly every discussion of health and well-being these days now leads to the gut, there is evidence that artificial sweeteners can adversely affect the numbers and diversity of the friendly bacteria in our intestines.

While artificial sweeteners can be a boon to people with conditions like diabetes, we believe that for the rest of us, they should be an occasional, rather than a regular, part of our diets.

(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 Doctors: We’re all pretty stressed-out, even the kids. I keep saying that spending a Saturday in the nice park near our house could help, but my husband just laughs. Isn’t there some kind of research that being outdoors is good for you?

Dear Reader: Just thinking about a walk under the open sky as we began our answer to you brought about a sigh of relief. It makes sense, because long before we humans started spending so much time in built environments, we were deeply connected to the natural world. Many people have an innate understanding about that connection, and years of research backs them up.

Studies show that regularly spending time outdoors confers a host of mental health benefits. These include relief of anxiety and stress, a boost to feelings of calm, enjoyment and well-being, and improvements to mood and attitude. And that’s not taking into account the positive effect that even mild exercise, like walking, has on the body.

It seems like the link between time spent in nature and emotional well-being would be hard to prove, but researchers from the University of Michigan in Ann Arbor found a way. In fact, according to their study, published in 2019 in the journal Frontiers in Psychology, as little as 20 minutes spent outside in nature can have a healing effect. As an added surprise, their study showed the connection holds up even when the green space is in an urban environment.

Over the course of two months, the researchers had 36 volunteers spend at least 10 minutes three times per week in a variety of outdoor environments. These included public parks, the green spaces near their places of work or their own backyards. The participants could either sit still or stroll around during their outdoor time, but they were banned from chatting, reading or using screens of any kind. In order to rule out the known benefits of exercise, they were also asked to refrain from vigorous physical activity prior to their nature walks.

Before and after each outing, samples of saliva, which contains the stress hormone cortisol, were collected from each volunteer. Analysis of the saliva samples revealed that the volunteers returned from their nature outings with lower levels of cortisol than they started out with. Surprisingly, the biggest drops in the stress hormone occurred in the first 20 to 30 minutes of nature immersion. Benefits continued after that, but more gradually. Neither the time of day that someone chose to be outdoors nor where they spent their time played a role in the stress reduction. According to this study, the simple act of stepping outside into a green space began to bring relief.

The time frame that this study reveals is certainly new, but research about the benefits of spending time in nature dates back to the 1970s. We hope that, with proximity to a park and the low bar of 20 to 30 minutes, you’ll be able to persuade your family to make being outdoors a regular part of their lives.

(Send your questions to askthedoctors@mednet.ucla.edu. Owing to the volume of mail, personal replies cannot be provided.)