Dear Doctor: My dad is 65 years old and has Type 2 diabetes. He recently developed pain in his feet, which his doctor says is peripheral neuropathy. What is that, and what treatments are available?

Dear Reader: Neuropathy is a condition in which the nervous system malfunctions due to either disease or some kind of damage. The addition of the word "peripheral" means the problem lies in the vast and complex network of nerves that serves the body.

The peripheral nervous system collects and sends vital sensory information to the central nervous system, which is made up of the brain and the spinal cord. When you drop that hot frying pan handle, break into a sweat on a hot day or keep your balance with your eyes closed, that's all thanks to information your peripheral nervous system has sent to your brain.

It's estimated that 20 million people in the United States experience some kind of peripheral neuropathy. Sometimes the damage is limited to a single nerve, but most often the condition affects groups of nerves. Symptoms include numbness, twitching, throbbing or tingling, burning sensations, problems with balance, or skin sensitivity so acute that ordinary stimuli, like the touch of a shirt on bare skin, are interpreted as pain.

When the motor nerves are affected, peripheral neuropathy causes muscle weakness and can often lead to the loss of muscle mass. If the nerves that serve the organs or glands are involved, it can result in impaired digestion, perspiration, urination or sexual function. At its most extreme, peripheral neuropathy causes breathing difficulties, or leads to organ failure. Fortunately, this is rare.

Diabetes is the most common cause of peripheral neuropathy. Other factors include infections such as shingles or the Epstein-Barr virus, certain kidney disorders, vitamin deficiencies, physical damage, cancers that press on or infiltrate nerve fibers, or autoimmune diseases that cause the body to attack its own tissues. Exposure to toxic industrial and environmental substances such as lead, arsenic or pesticides as well as medical agents like chemotherapy drugs can also lead to the condition. So can heavy alcohol consumption.

Your father's symptoms began in his feet, which is common among people with diabetes. He may also experience numbness, a decrease in foot and ankle reflexes, trouble with balance and coordination, and an increase in foot problems like ulcers and infections. This is due to tissue damage resulting from chronic high blood glucose levels, as well as decreased circulation, which occurs because diabetes causes the blood vessels in the foot and leg to become stiff and grow narrow.

Treatment for your father's condition will focus on two things -- carefully controlling his diabetes to prevent further nerve damage, and giving him relief from the existing pain. Mild pain often responds to over-the-counter NSAIDs. Medications like antidepressants, anticonvulsants and narcotics are used for chronic pain. Procedures like electrical nerve stimulation have shown promise. Physical therapy and specialized footwear can also help.

Pain treatment is often most effective when there's an ongoing dialogue. Be sure your dad shares all his symptoms with his doctor, and follows up with regular progress reports.

(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 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.)