Dear Doctor: Is walking or running on a treadmill as good as walking or running on concrete streets or sidewalks?

Dear Reader: This is an interesting question, because the definition of "as good as" is quite ambiguous. Good can be defined as having cardiovascular, or other, health benefits, but it can also be defined as having mental or social health benefits, such as those that come from running or walking with another person. For the purposes of this question, let's look at the cardiovascular aspects.

A 1985 study in the journal Medicine & Science in Sports & Exercise measured the amount of oxygen consumed during both treadmill running and outdoor running. The level of oxygen consumption, termed VO2, is a measure of energy expenditure with exercise. The subjects ran 950 meters on a treadmill and outdoors. The subjects also ran at varying speeds and at different elevation grades. The investigators found no difference in the amounts of oxygen consumed with either the outdoor or treadmill running. This was consistently seen, even when there were changes in speed or elevation grade.

A 1996 study in the Journal of Sports Sciences similarly looked at the differences in VO2 in nine athletes who ran both outside and on treadmills at varying speeds and elevation grades. This study showed some significant differences in the VO2 between outside and treadmill running. Overall, those who exercised outside consumed more oxygen than those on a treadmill. This may be partially related to the wind resistance seen with outdoor exercise.

The authors concluded that running outside on flat terrain was similar to treadmill running at a 1 percent elevation grade. So, if you want to equate your treadmill running to what you might experience outside, place your treadmill at a 1 percent grade.

But treadmill running is quite dissimilar from outdoor running in one respect: Your muscles respond differently. Because a treadmill is powered by a machine, not your body, the hamstring muscles are not used as much -- something you may notice if you normally run on a treadmill and then decide to go running outside. In that case, to prevent an injury, slow your pace.

A significant benefit from running on a treadmill is that the belt of the treadmill is much more forgiving than the concrete of the sidewalk. While there has been no long-term study regarding the benefit of treadmill running on the joints, it stands to reason that exercising on a treadmill could decrease the incidence of knee and back injuries.

Alternatively, one definite positive from outdoor running is that it's less monotonous than treadmill running. The changes of scenery and terrain keep things interesting. When I run on a trail, I am constantly looking at the rocks I have to avoid, and I often have to move laterally to follow the trail. When I get to the top of the mountain, looking down at the expanse of earth below me, I get a perspective that is much different than running on a treadmill. This cannot be measured, but it motivates me to run again.

If you like running or walking on a treadmill, by all means continue doing this. The cardiovascular benefits are similar to outdoor exercise, and it may be less hard on your joints. The most important thing is to take the time and exercise, whether it be inside or outside.

(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.)

Dear Doctor: When it's our turn to bring team snacks to the kids' weekend soccer games, the most challenging part is accommodating so many allergies, especially to peanuts. Is it true that there's now a way to keep children from getting a peanut allergy in the first place?

Dear Reader: Food allergies among kids are a fact of life. In fact, the number of children who are allergic to one or more foods has increased by close to 50 percent in recent years. According to the Centers for Disease Control and Prevention, food allergies affect 6 percent of American children.

An allergy occurs when the immune system flags a certain food as harmful, which sets off a physical reaction to that food. The most common triggers are milk, eggs, soy, wheat, fish, shellfish, tree nuts and, as you point out, peanuts. Children with siblings who have a food allergy, or who have eczema or asthma, are at higher risk of developing a food allergy.

For a child with an allergy, even a trace of the problem food can cause reactions that range from mild to severe. These include hives, rash, stomach and digestive upset, headache, nasal congestion, itchy eyes and breathing problems. In some cases, reactions can be so extreme as to be life-threatening.

The reasons for the recent surge in food allergies aren't entirely clear. But several new studies into peanut allergies in children have both overturned accepted wisdom and offered parents new hope.

In the past, parents had been told to avoid feeding peanuts, or anything containing peanuts, to children at risk of developing an allergy until they reached the age of 3. But some researchers questioned that approach. Instead, they began to investigate whether early exposure to peanuts could actually prevent an allergy from developing.

In a landmark study, infants at high risk of developing a peanut allergy were divided into two groups. One group was given a snack that contained peanuts starting between the ages of 4 and 11 months, and until they turned 5. The children in the other group avoided peanuts. At the end of the study, the children who ate peanuts were more than 80 percent less likely to have a peanut allergy than those whose diet was peanut-free.

The upshot is that the National Institute of Allergy and Infectious Diseases has issued new guidelines. The institute now proposes that children who are at risk of a peanut allergy can eat products that contain peanuts beginning when they are between 4 and 6 months of age. But -- and this is crucial -- only after they have been first tested to make sure they don't already have a peanut allergy.

Our position, as always, is that you should first discuss this issue with your pediatrician or primary care physician. With your doctor as both partner and guide, you have the best chance at a good and safe outcome.

(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.)

Dear Doctor: My wife's uncle, who lives with us, is 76 and obese. I have noticed he sleeps an awful lot -- to me, anyway. He sleeps approximately five or six hours a night and then later while sitting on the couch. He frequently takes afternoon naps or will fall asleep while reading and will also fall asleep while watching TV at night. My wife doesn't seem to be concerned. Should we be?

Dear Reader: The quick answer is yes, you should be worried. I wouldn't assume that your wife's uncle's sleepiness is a function of age. I don't know the specifics about his past medical conditions or other aspects of his overall health, but the details you provide make me suspect sleep apnea.

Obstructive sleep apnea is a common disorder, affecting 15 percent of adult males, that occurs when people are sleeping. The biggest risk factors are obesity, being male and older age. Your wife's uncle has all three of these. In a 2000 study of 700 adults, published in the Journal of the American Medical Association, every 10 percent increase in weight is associated with a sixfold increase in the rate of sleep apnea. With the rates of obesity increasing over the last 30 years, the rates of sleep apnea have also increased.

In sleep apnea, lying flat creates an obstruction of the airway, so much so that the person stops breathing. This is noted as a pause in breathing that can last for a few seconds to longer than a minute. What the partners of sleep apnea patients typically hear is snoring that stops when the patient's airway obstructs. This is followed by a lack of breathing sounds, then a gasping of air as the patient tries to recover his or her breathing. Patients themselves don't notice this pattern.

Because sleep apnea interferes with deep sleep (stages 3 and 4), sleepiness and fatigue are the most common signs of sleep apnea. But the risks go beyond sleepiness. Chronic sleep apnea in men leads to a higher risk of hypertension and diabetes and lower testosterone levels. Over the years, sleep apnea places stress upon the heart, increasing the risk of heart attacks and strokes. Further, sleep apnea increases the risk of abnormal heart rhythms in the middle of the night, which can lead to sudden death. Considering the degree of your wife's uncle's daytime sleepiness, he may have severe sleep apnea.

I would voice these concerns to your wife's family members, and urge them to enroll him in a sleep study for a definitive diagnosis. I have many patients whom I suspect of having sleep apnea, but who are reluctant to take part in a sleep study because they don't want to sleep in a lab, even one designed for sleep. If your uncle shares that fear, tell him -- as I tell my patients -- that a sleep study can also be done in the comfort of their own home with a monitor hooked up in the house.

After diagnosis comes treatment. Sleep apnea is correctable with use of a pressure mask that keeps the airway open, called CPAP, for continuous positive airway pressure.

That's not to say CPAP is an easy cure. Many people have difficulty using this mask at night, and still others don't want to investigate the possibility of sleep apnea for fear of having to wear a mask over their face all night.

For those who have difficulty with CPAP, a device called a mandibular advancement device is also an option. This device acts like a rigid retainer to push the lower jaw forward and open up the airway.

Despite the unpleasantness of the remedies, your wife's uncle and family should be made aware that sleeping all day isn't normal and that a sleep study is vital. The health risks are too great to ignore.

(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.)