Dear Doctor: I'm 35 years old and a regular exerciser. Sometimes, though, when I'm on vacation or just want to veg out, I need a break. Now I'm hearing that this is really bad for your metabolism, especially as you get older. Seriously? Taking a couple of weeks off really makes that much difference?

Dear Reader: We're sorry to rain on your hammock time, but the newest research suggests that yes, taking as little as a two-week break from your regular exercise routine has negative health effects for older adults that can be long-lasting. This new insight comes from two recent studies that looked at what happened when physically active adults stopped exercising, even for a short time. Among the ill effects was a rise in blood sugar levels, a drop in insulin sensitivity and weight gain. As though that wasn't enough bad news, it turned out that even after the study participants returned to their regular exercise regimens, the metabolic changes were slow to fully reverse.

A study conducted by researchers from the University of Liverpool in England looked at a group of 45 men and women between the ages of 24 and 50 who were quite active. They each walked more than 10,000 steps per day, did not have diabetes and were metabolically fit. When the study participants were asked to suddenly cut down on their exercise and begin sitting for at least 3 1/2 hours per day, their metabolisms changed. Over the course of the two weeks that the participants slowed down -- their activity monitors logged under 2,000 steps per day -- their blood sugar spiked, they showed signs of insulin resistance, and their blood lipid results started to become distinctly less healthy. Not only did they lose muscle mass in their legs, they gained fat around their middles. Although most of them recovered their lost ground when they began to exercise again, several of the participants showed ongoing signs of insulin resistance.

A second study from Canada's McMaster University focused on adults aged 65 and older. In that study, the participants were also active, walking between 7,000 and 8,000 steps per day. However, in this case, they all had elevated blood sugar levels, which put them at risk of developing Type 2 diabetes. As with the Liverpool study, these adults were asked to drastically reduce their activity levels to below 1,000 steps per day, and to spend several hours sitting.

They suffered the same ill-effects as their younger peers, but more quickly and more severely. In fact, the sudden lack of exercise pushed some participants dangerously close to developing Type 2 diabetes, and they had to stop their participation in the study. Another difference between this group and the younger participants is that even after resuming normal activity for two weeks, most had not made up the metabolic ground lost to their enforced inactivity.

Yes, these are small studies, and more research is needed. But based on conclusions thus far, it appears that when we stop being active for weeks at a time, we pay a significant price.

(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 mother and my sister are both night owls who stay up late and sleep late the next morning. In our family we never thought anything of it. But now it turns out their sleeping habits are something called "delayed sleep phase disorder." Why is being a night owl considered to be a disorder? Can it be cured?

Dear Reader: Although in the past the sleep cycle you've described was called a disorder, it is now more often referred to as a syndrome. Specifically, it's when someone's sleep cycles are delayed by two or more hours, which puts the individual out of step with the majority of the people around them.

It was once believed that being a night owl was simply a preference, or perhaps even a psychological issue, but new research ties it to the workings of the individual's body clock, or more specifically, circadian rhythm. This is an internal system that regulates not only the cycle of sleep and waking, but also a range of metabolic functions that include body temperature, hormone secretion, digestion and even wound healing. The master body clock oversees circadian rhythms, which are influenced by factors within the body. Circadian rhythms are also are tied to the cycles of light and dark as the sun rises and sets.

Someone with delayed sleep phase syndrome, or DSPS, is unable to fall asleep at the typical bedtime of 9, 10 or 11 p.m. Instead, these individuals often report that when the rest of the world is nodding off, they are coming to life. Staying up until the early morning hours shifts their optimal time of awakening as well.

But due to real-world responsibilities like work, school and family, people with DSPS are often forced to rise long before they get an adequate amount of sleep. This leads to daytime drowsiness; it has also been linked to depression. A recent study, which analyzed the sleep habits of 430,000 adults for 6 1/2 years, found that so-called night owls were more likely to develop diabetes and neurological disorders. It also found a 10 percent increase in premature death when compared to early-to-bed sleepers.

The good news is that, other than the time shift, people with DSPS don't usually have other sleep issues such as interrupted sleep or insomnia. When left to their own devices, they go to bed late, sleep well, then rise late, feeling refreshed.

For those who want to switch to more traditional sleep habits, a number of treatments have proven effective. The challenge is that not everything works for everyone, so a period of experimentation is often required, often with the help of a sleep specialist. Approaches include bright light therapy, which is believed to shift the circadian clock. Another is phase-delay chronotherapy, in which bedtimes are set progressively later until, at the end of a set period of time, the desired bedtime has been reached. The theory here is that adjusting to a later bedtime is easier than to an earlier one. Medications like melatonin can be helpful, and some people use sleep aids when they hit a rough patch. The important thing in all of these approaches is consistency.

(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: Our dad had a mild stroke about a year ago and has been taking daily low-dose aspirin ever since. But I just heard about a new study that says this kind of therapy isn't actually helpful and might even be dangerous. Is this true? Should he stop? I'm confused!

Dear Reader: We've been hearing from patients (and some friends and family) that they're also confused by the new aspirin study you're referring to. The truth is that while low-dose aspirin has indeed been associated with improved health outcomes for individuals like your father who have previously experienced a stroke or a heart attack, the idea of aspirin therapy as a hedge against cardiovascular disease in healthy adults has always been under debate. Now, a trio of studies published in September in the New England Journal of Medicine pave the way for a clearer understanding of the effects of low-dose aspirin therapy.

In the main study, which lasted about five years, researchers in Australia looked at the effects of low-dose aspirin therapy in 20,000 people with a median age of 74. Each person was in good health at the time that he or she entered the study, without a history of heart disease. Unlike the observational studies we've discussed lately, which draw conclusions from data in which variables are not under the researchers' control, this was a randomized, double-blind, placebo-controlled trial. That means that half of the study participants took aspirin and half took a placebo. Study participants were randomly assigned to the two groups, and the double-blind part means that neither the participants nor the researchers knew which group was getting aspirin and which was getting the placebo.

Bottom line: This is the best type of study to figure out whether a specific exposure, in this case aspirin, is directly responsible for a particular outcome.

When the study was concluded, it turned out there was no observable difference in "disability-free survival" between the two groups. That is, low-dose aspirin therapy did not deliver additional health protections. What was different between the two groups was that over the course of the study, the participants taking low-dose aspirin had a measurably higher incidence of bleeding, some of it life-threatening. This finding was corroborated by two additional studies, which uncovered a higher risk of major hemorrhage among the aspirin group, as well as a higher incidence of "all-cause mortality." The authors of the studies appear to be somewhat surprised by the results, which they called "unexpected."

It's important to keep in mind that the participants in these studies were all healthy adults without heart disease or stroke. However, for those individuals who have already had a heart attack or stroke, or who do have cardiac disease and other comorbidities, such as diabetes, there is significant data to support aspirin use. It is our opinion that those patients should not stop their aspirin regimens based on these findings.

(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.)