Exercise gives older men a better brain boost
Men have stronger positive correlation between fitness and brain function
February 13, 2019
Science Daily/American Physiological Society
New research suggests that the relationship between physical and brain fitness varies in older adults by virtue of their sex.
Cardiorespiratory fitness is the measure of how much -- and how well -- oxygen is delivered to the muscles during exercise. Fitness level has also been associated with changes in the brain's nerve-rich tissue, called gray matter, and better cognitive function in later life. Previous studies have also found cardiorespiratory fitness to be related to how the brain functions during periods of rest. Nerve connectivity in the brain during rest changes with age. These changes can negatively affect cognitive function. However, "the neural basis of sex differences in the relationship between fitness and brain function in older adults has not been directly explored," wrote researchers from York University and McGill University in Canada.
The research team studied one group of men and one of women, both with an average age of 67. The volunteers self-reported their typical daily physical activity level. The research team recorded the participants' height, weight, age, sex and resting heart rate to determine their cardiorespiratory fitness. They also administered imaging tests of the brain to record nerve function both within specific brain networks (local efficiency) and among all networks (global efficiency).
The men were found to have higher cardiorespiratory fitness levels than the women. However, the women had higher local network efficiency and lower global network efficiency than the men. This pattern of connectivity was more robust in the women and has been positively associated with executive function, which are skills that contribute to being able to focus, pay attention and manage time. Fitness levels, however, were more strongly associated with improving this brain efficiency pattern for men than women.
"Our findings that [cardiorespiratory fitness] is associated with brain function in a sex-dependent manner underscore the importance of considering sex as a factor when studying associations between exercise and brain health in older adulthood," the researchers wrote.
https://www.sciencedaily.com/releases/2019/02/190213124408.htm
Keeping active in middle age may be tied to lower risk of dementia
February 25, 2019
Science Daily/University of Gothenburg
Keeping physically and mentally active in middle age may be tied to a lower risk of developing dementia decades later, according to a new study. Mental activities included reading, playing instruments, singing in a choir, visiting concerts, gardening, doing needlework or attending religious services.
"These results indicate that these activities in middle age may play a role in preventing dementia in old age and preserving cognitive health," said study author Jenna Najar, MD, from Sahlgrenska Academy, University of Gothenburg.
"It's exciting as these are activities that people can incorporate into their lives pretty easily and without a lot of expense."
The study involved 800 Swedish women with an average age of 47 who were followed for 44 years. At the beginning of the study, participants were asked about their mental and physical activities.
Mental activities included intellectual activities, such as reading and writing; artistic activities, such as going to a concert or singing in a choir; manual activities, such as needlework or gardening; club activities; and religious activity.
Participants were given scores in each of the five areas based on how often they participated in mental activities, with a score of zero for no or low activity, one for moderate activity and two for high activity. For example, moderate artistic activity was defined as attending a concert, play or art exhibit during the last six months, while high artistic activity was defined as more frequent visits, playing an instrument, singing in a choir or painting. The total score possible was 10.
Participants were divided into two groups. The low group, with 44 percent of participants, had scores of zero to two and the high group, with 56 percent of participants, had scores of three to 10.
For physical activity, participants were divided into two groups, active and inactive. The active group ranged from light physical activity such as walking, gardening, bowling or biking for a minimum of four hours per week to regular intense exercise such as running or swimming several times a week or engaging in competitive sports. A total of 17 percent of the participants were in the inactive group and 82 percent were in the active group.
During the study, 194 women developed dementia. Of those, 102 had Alzheimer's disease, 27 had vascular dementia and 41 had mixed dementia, which is when more than one type of dementia is present, such as the plaques and tangles of Alzheimer's disease along with the blood vessel changes seen in vascular dementia.
The study found that women with a high level of mental activities were 46 percent less likely to develop Alzheimer's disease and 34 percent less likely to develop dementia overall than the women with the low level of mental activities. The women who were physically active were 52 percent less likely to develop dementia with cerebrovascular disease and 56 percent less likely to develop mixed dementia than the women who were inactive.
The researchers took into account other factors that could affect the risk of dementia, such as high blood pressure, smoking and diabetes. They also ran the results again after excluding women who developed dementia about halfway through the study to rule out the possibility that those women may have been in the prodromal stage of dementia, with less participation in the activities as an early symptom. The results were similar, except that physical activity was then associated with a 34-percent reduced risk of dementia overall.
Of the 438 women with the high level of mental activity, 104 developed dementia, compared to 90 of the 347 women with the low level of activity. Of the 648 women with the high level of physical activity, 159 developed dementia, compared to 35 of the 137 women who were inactive.
https://www.sciencedaily.com/releases/2019/02/190225145650.htm
Concussion treatment: Adolescent athletes 'prescribed' aerobic exercise recovered faster
Study is the first randomized clinical trial on treatment of acute concussion
Science Daily/February 4, 2019
University at Buffalo
Adolescent athletes who sustained concussions while playing a sport recovered more quickly when they underwent a supervised, aerobic exercise regimen.
The study, by University at Buffalo researchers and colleagues, is the first randomized clinical trial of a treatment in the acute phase after a sport-related concussion. The goal was to evaluate prescribed, progressive sub-symptom threshold exercise as a treatment within the first week of a concussion in adolescents after a few days of rest. Sub-symptom threshold exercise is physical activity that doesn't exacerbate symptoms.
The researchers followed 103 participants ages 13-18, with nearly the same number of males and females. All were seen within 10 days after sustaining a sport-related concussion at one of the UBMD Orthopaedics and Sports Medicine clinics in Western New York or at the Pan Am Clinic in Winnipeg.
Patients who followed the aerobic exercise program took on average 13 days to recover while those in the control group, who performed stretching exercises, took 17 days. In addition, fewer patients in the exercise program took longer than four weeks to recover than did patients in the control group.
"This research provides the strongest evidence yet that a prescribed, individualized aerobic exercise program that keeps the heart rate below the point where symptoms worsen is the best way to treat concussion in adolescents," said John J. Leddy, MD, first author, clinical professor of orthopaedics in the Jacobs School of Medicine and Biomedical Sciences at UB, and director of the UB Concussion Management Clinic at UBMD Orthopaedics and Sports Medicine.
The researchers plan to investigate if the treatment is also effective in adults with concussion.
No proven treatment
The researchers noted that there is no proven treatment for concussion, especially among adolescents, who typically take the longest to recover.
"Until now, nothing else has been proven in any way effective for treating concussion," said Barry S. Willer, PhD, senior author, director of research in the UB Concussion Management Clinic and professor of psychiatry in the Jacobs School. "This is the best evidence so far for a treatment that works."
The findings directly contradict the conventional approach to concussion, which often consists of nearly total rest, eliminating most physical and mental activities, including schoolwork.
"Telling a teenager to go home and basically do nothing is depressing," said Willer. "It can actually increase their physical and psychological symptoms, and we see that particularly among girls. But with our approach, you're saying, sure, you can return to school and you should start doing these exercises. Their chins are up, Mom and Dad are happy and so is the student."
The fact that all states have now passed laws requiring schools to make accommodations for students who have sustained concussions is also helpful, said Willer, so that the student can opt out of some activities during the school day, if necessary.
The proper 'dose' of exercise
To determine how much exercise each patient could sustain without exacerbating symptoms, the researchers had each one undergo the Buffalo Concussion Treadmill Test, developed by Leddy and Willer, to determine at what level their symptoms worsen. As the patient walks on a treadmill, the incline is gradually increased and the heart rate is recorded at the point where concussion symptoms intensify.
"We prescribed exercise at 80 percent of that threshold," Leddy explained, "so each patient's exercise 'dose' was individually tailored."
Patients were randomly assigned to the aerobic exercise group (52) or to a stretching group (51). Patients in both groups were sent home with a heart rate monitor so they could make sure they stayed below the threshold while exercising.
Both groups performed their assigned exercise for about 20 minutes each day and were required to report compliance and daily symptoms online. Those in the aerobic group either walked on a treadmill, rode a stationary bike, or walked either inside or out. Aside from the prescribed exercise, patients were advised to refrain from contact sports, gym class or team practice. They were given advice about getting schoolwork done and told to avoid excessive use of electronic devices, since that can also aggravate symptoms.
Each patient's condition was re-evaluated weekly and as symptoms improved, the "dose" of exercise or stretching was increased, according to the weekly treadmill test results.
Recovery was rigorously defined, requiring agreement among three independent criteria: the patient's reporting a normal (minimal) level of symptoms, a normal physical examination by a medical doctor, and the return of normal exercise tolerance on the Buffalo Concussion Treadmill Test. The physicians were blinded as to the group assignment of each participant.
One surprising finding was that only two participants out of 52 (4 percent) in the aerobic exercise group took longer than four weeks to recover compared to seven out of 51 (14 percent) in the stretching group. This did not reach statistical significance, but the scientific literature suggests, by contrast, that between 15 and 25 percent of adolescents who do not receive any treatment will be symptomatic past four weeks.
"Reducing the number of concussed adolescents who have delayed recovery has major implications," Willer said, noting that delayed recovery creates more difficulty with schoolwork, can lead to depression and puts additional demands on the health care system and its costs.
Expanding capacity for medically supervised exercise treatment
Michael J. Ellis, MD, co-author and medical director of the Pan Am Concussion Program in the Department of Surgery and Pediatrics at the University of Manitoba, said that for years, his clinic has been successfully using the Buffalo Concussion Treadmill Test and a medically supervised sub-symptom-threshold aerobic exercise program to treat professional, collegiate and elite adolescent athletes.
Expanding access to this treatment is now critical, he said.
"The results of this study suggest that we must build greater capacity within our health care systems to allow patients access to multidisciplinary concussion programs and clinics that have the medical expertise to carry out early targeted rehabilitation of acute concussion," he said.
Leddy and Willer are internationally known for their research into the best ways to diagnose and treat concussion, especially among adolescents, who are the most vulnerable age group for concussions and take the longest time to recover. They have led the emerging body of research findings that show that a patient's degree of exercise intolerance in the first week after injury, i.e., the lower the threshold of activity at which symptoms increase, is a key clinical indicator of how severe the concussion may be.
https://www.sciencedaily.com/releases/2019/02/190204114615.htm
Working it out: Researchers find exercise may help fight depression in seniors
February 7, 2019
Science Daily/McMaster University
The benefits of exercise are widely known but kinesiologists have for the first time found that physical activity may help fight depression in seniors by stimulating muscle-generated mood boosters.
The findings, published in the American Journal of Physiology -- Cell Physiology, reveal that the underlying mechanisms which make us feel good when we exercise persist into old age and highlight the importance of staying active.
"A previous study demonstrated these mechanisms in healthy young adults, however, it was unknown whether the muscle deterioration which accompanies aging would preclude older adults from achieving similar exercise-induced benefits," explains David Allison, lead author on the study and a postdoctoral fellow in McMaster's Department of Kinesiology.
"This could have important implications concerning the use of exercise as a treatment or a preventative strategy for depression in seniors," he says.
Little is known about the relationship between skeletal muscle and mental health, or how exercise impacts this relationship.
Earlier research has shown that physical activity may help to 'turn on' genes within skeletal muscle which can then influence the key metabolic pathways that ultimately promote mood-enhancing chemicals, such as serotonin, within the brain.
Muscle loss is a common problem in the elderly which may restrict that pathway and therefore increase the risk for depression, says Allison.
For the study, a group of healthy men, aged 65 and over, followed a 12-week protocol of high-intensity interval training (HIIT) on a stationary bike once a week combined with bi-weekly strength training sessions.
Researchers analyzed blood samples and changes to muscle and determined that three months of exercise was enough to enhance gene expression within the skeletal muscle.
"Even individuals who are already metabolically healthy -- with good weight, good blood pressure and blood sugar levels -- need to prioritize regular physical activity to maintain or improve upon their mental health," says Allison. "We have shown such benefits are still achievable in old age and further emphasize the importance of maintaining an active lifestyle."
In the future, researchers hope to explore the relationship between mental health and exercise among the clinically depressed to see if similar biochemical changes can be achieved.
https://www.sciencedaily.com/releases/2019/02/190207111309.htm
Exercise may improve thinking skills in people as young as 20
January 30, 2019
Science Daily/American Academy of Neurology
Regular aerobic exercise such as walking, cycling or climbing stairs may improve thinking skills not only in older people but in young people as well, according to a new study. The study also found that the positive effect of exercise on thinking skills may increase as people age.
The specific set of thinking skills that improved with exercise is called executive function. Executive function is a person's ability to regulate their own behavior, pay attention, organize and achieve goals.
"As people age, there can be a decline in thinking skills, however our study shows that getting regular exercise may help slow or even prevent such decline," said study author Yaakov Stern, PhD, of Columbia University in New York, and a member of the American Academy of Neurology. "We found that all participants who exercised not only showed improvements in executive function but also increased the thickness in an area of the outer layer of their brain."
The study involved 132 people between the ages of 20 and 67 who did not smoke or have dementia but who also did not exercise at the start of the study and were determined to have below average fitness levels. Participants were randomly assigned to six months of either aerobic exercise or stretching and toning four times a week. The two groups were equally balanced for age, sex, education as well as memory and thinking skills at the start of the study.
All participants either exercised or stretched and toned at a fitness center and checked in weekly with coaches monitoring their progress. They all wore heart rate monitors as well. Participants' thinking and memory skills were evaluated at the start of the study as well as at three months and at the end of the six-month study.
Participants in the exercise group chose from aerobic activities including walking on a treadmill, cycling on a stationary bike or using an elliptical machine. They ramped up their activity during the first month, then during the remainder of the six-month study they trained at 75 percent of their maximum heart rate. People in the stretching and toning group did exercises to promote flexibility and core strength.
Researchers measured participants' aerobic capacity using a cycling machine called an ergometer that estimates exercise intensity. Participants also had MRI brain scans at the start and end of the study.
Researchers found that aerobic exercise increased thinking skills. From the beginning of the study to the end, those who did aerobic exercise improved their overall scores on executive function tests by 0.50 points, which was a statistically significant difference from those who did stretching and toning, who improved by 0.25 points. At age 40, the improvement in thinking skills was 0.228 standard deviation units higher in those who exercised compared to those who did stretching and toning and at age 60, it was 0.596 standard deviation units higher.
"Since a difference of 0.5 standard deviations is equivalent to 20 years of age-related difference in performance on these tests, the people who exercised were testing as if they were about 10 years younger at age 40 and about 20 years younger at age 60," Stern said.
He added, "Since thinking skills at the start of the study were poorer for participants who were older, our findings suggest that aerobic exercise is more likely to improve age-related declines in thinking skills rather than improve performance in those without a decline."
Researchers also found an increase in the thickness of the outer layer of the brain in the left frontal area in all those who exercised, suggesting that aerobic exercise contributes to brain fitness at all ages.
"Our research confirms that exercise can be beneficial to adults of any age," said Stern.
Overall, researchers did not find a link between exercise and improved memory skills. However, those with the genetic marker for dementia, the APOE ?4 allele, showed less improvement in thinking skills.
A limitation of the study is the small number of participants. Larger studies over longer periods of time may allow researchers to see other effects in thinking and memory skills.
The study was supported by the National Institutes of Health.
https://www.sciencedaily.com/releases/2019/01/190130161638.htm
How exercise may protect against Alzheimer's
February 8, 2019
Science Daily/Columbia University Irving Medical Center
A hormone called irisin -- produced during exercise -- may protect neurons against Alzheimer's disease.
Athletes know a vigorous workout can release a flood of endorphins: "feel-good" hormones that boost mood. Now there's evidence that exercise produces another hormone that may improve memory and protect against Alzheimer's disease, according to a study co-led by Ottavio Arancio, MD, PhD, a researcher at Columbia University's Vagelos College of Physicians and Surgeons and Taub Institute for Research on Alzheimer's Disease and the Aging Brain.
The study was published in Nature Medicine.
Physical activity is known to improve memory, and studies suggest it may also reduce the risk of Alzheimer's disease. But researchers don't understand why.
A few years ago, exercise researchers discovered a hormone called irisin that is released into the circulation during physical activity. Initial studies suggested that irisin mainly played a role in energy metabolism. But newer research found that the hormone may also promote neuronal growth in the brain's hippocampus, a region critical for learning and memory.
"This raised the possibility that irisin may help explain why physical activity improves memory and seems to play a protective role in brain disorders such as Alzheimer's disease" says Arancio, who is a professor of pathology and cell biology and of medicine at Columbia University Vagelos College of Physicians and Surgeons.
Irisin is reduced in brains of people with Alzheimer's
In the new study, Arancio and his colleagues at the Federal University of Rio de Janeiro in Brazil and Queens University in Canada first looked for a link between irisin and Alzheimer's in people. Using tissue samples from brain banks, they found that irisin is present in the human hippocampus and that hippocampal levels of the hormone are reduced in individuals with Alzheimer's.
To explore what irisin does in the brain, the team turned to mice. These experiments show that irisin, in mice, protects the brain's synapses and the animals' memory: When irisin was disabled in the hippocampus of healthy mice, synapses and memory weakened. Similarly, boosting brain levels of irisin improved both measures of brain health.
Swimming boosts irisin, protects memory in mice
The researchers then looked at the effect of exercise on irisin and the brain. In the study's most compelling experiments, the researchers found that mice who swam nearly every day for five weeks did not develop memory impairment despite getting infusions of beta amyloid -- the neuron-clogging, memory-robbing protein implicated in Alzheimer's.
Blocking irisin with a drug completely eliminated the benefits of swimming, the researchers also found. Mice who swam and were treated with irisin-blocking substances performed no better on memory tests than sedentary animals after infusions with beta amyloid.
Together the findings suggest that irisin could be exploited to find a novel therapy for preventing or treating dementia in humans, Arancio says. His team is now searching for pharmaceutical compounds that can increase brain levels of the hormone or can mimic its action.
"In the meantime, I would certainly encourage everyone to exercise, to promote brain function and overall health," he said. "But that's not possible for many people, especially those with age-related conditions like heart disease, arthritis, or dementia. For those individuals, there's a particular need for drugs that can mimic the effects of irisin and protect synapses and prevent cognitive decline."
https://www.sciencedaily.com/releases/2019/02/190208173511.htm
Want healthier eating habits? Start with a workout
January 30, 2019
Science Daily/University of Texas at Austin
Researchers have found that formerly sedentary young adults who were instructed to exercise regularly for several weeks started choosing healthier foods without being asked to.
In the latest evidence that it's worth sticking to your health-focused New Year's resolutions, researchers at the University of Texas at Austin have found that exercising regularly is linked to better eating habits.
The new study, published this week in the International Journal of Obesity, looked at 2,680 young adults who were not exercising regularly or dieting. Scientists found that after exercising for several weeks, formerly sedentary study participants were more likely to choose foods like lean meats, fruits and vegetables, while preferences for fried foods, sodas and other unhealthy options decreased.
Participants were instructed not to change their diets in any significant way, but it happened anyway. Although this study did not examine the mechanism at work behind the changes, previous research has found that moderate exercise can reduce a preference for high-fat foods in animals through changes in dopamine levels. Several studies also have shown a relationship between the intensity of exercise and the amount of appetite-regulating hormones in the body.
"The process of becoming physically active can influence dietary behavior," said Molly Bray, corresponding author of the paper and chair of the Nutritional Sciences department at UT Austin and a pediatrics faculty member at Dell Medical School. "One of the reasons that we need to promote exercise is for the healthy habits it can create in other areas. That combination is very powerful."
Bray says what drives food-preference changes when people exercise would probably be consistent across a wide span of ages. The study examined people between the ages of 18 and 35, a period of young adulthood critical for forming healthy habits. Previous studies have found that considerable weight gain occurs during the college years and that being mildly to moderately overweight at age 20-22 increases the risk of obesity later in life.
"Many people in the study didn't know they had this active, healthy person inside them," Bray said. "Some of them thought their size was inevitable. For many of these young people, they are choosing what to eat and when to exercise for the first time in their lives."
The participants in the study were students at the University of Houston and the University of Alabama at Birmingham. Participants who said they exercised less than 30 minutes a week at the beginning of the study started 30-minute aerobic workouts three times a week for 15 weeks, with instructions not to change their diet in any significant way. The exercise sessions consisted of 30 minutes of aerobic exercise at 65-85 percent of the person's age- and gender-specific maximum heart rate, along with a 5-minute warmup and a 5-minute cool down. Participants wore heart-rate monitors and could choose from a variety of exercise types, such as on stationary bikes, treadmills or elliptical machines.
https://www.sciencedaily.com/releases/2019/01/190130112728.htm
Low-carb diets cause people to burn more calories
All calories are not alike, finds largest, longest macronutrient feeding trial to date
November 14, 2018
Science Daily/Boston Children's Hospital
Most people regain the weight they lose from dieting within one or two years, in part because the body adapts by slowing metabolism and burning fewer calories. A meticulous study now finds that eating fewer carbohydrates increases the number of calories burned. The findings suggest that low-carb diets can help people maintain weight loss, making obesity treatment more effective.
The study, known as the Framingham State Food Study, or (FS)2, tightly controlled what people ate by providing them with fully prepared food-service meals for a 20-week period. Researchers carefully tracked participants' weight and measured insulin secretion, metabolic hormones and total energy expenditure (calories burned).
"This is the largest and longest feeding study to test the 'Carbohydrate-Insulin Model,' which provides a new way to think about and treat obesity," says David Ludwig, MD, PhD, who is co-principal investigator with Cara Ebbeling, PhD. (Ludwig and Ebbeling are co-directors of the New Balance Foundation Obesity Prevention Center in Boston Children's Division of Endocrinology.) "According to this model, the processed carbohydrates that flooded our diets during the low-fat era have raised insulin levels, driving fat cells to store excessive calories. With fewer calories available to the rest of the body, hunger increases and metabolism slows -- a recipe for weight gain."
Comparing carb levels head to head
After careful telephone screening of 1,685 potential participants, Ebbeling, Ludwig and colleagues enrolled 234 overweight adults (age 18 to 65, body mass index of 25 or higher) to an initial weight-loss diet for about 10 weeks. Of these, 164 achieved the goal of losing 10 to 14 percent of body weight and went on to the study's maintenance phase.
These participants were then randomized to follow high-, moderate- or low-carbohydrate diets for an additional 20 weeks -- with carbs comprising 60, 40 and 20 percent of total calories, respectively. Carbs provided to all three groups were of high quality, conforming to guidelines for minimizing sugar and using whole rather than highly processed grains.
In all three groups, total calorie intake was adjusted to maintain weight loss, so participants' weight did not change notably. During this phase, the goal was to compare energy expenditure -- how the different groups burned calories at the same weight. Energy expenditure was measured by a gold-standard method using doubly labeled water.
Over the 20 weeks, total energy expenditure was significantly greater on the low-carbohydrate diet versus the high-carbohydrate diet. At the same average body weight, participants who consumed the low-carb diet burned about 250 kilocalories a day more than those on the high-carb diet.
"If this difference persists -- and we saw no drop-off during the 20 weeks of our study -- the effect would translate into about a 20-pound weight loss after three years, with no change in calorie intake," says Ebbeling.
In people with the highest insulin secretion at baseline, the difference in calorie expenditure between the low- and high-carb diets was even greater, about 400 kilocalories per day, consistent with what the Carbohydrate-Insulin Model would predict. Ghrelin, a hormone thought to reduce calorie burning, was significantly lower on the low- versus high-carb diet.
"Our observations challenge the belief that all calories are the same to the body," says Ebbeling. "Our study did not measure hunger and satiety, but other studies suggest that low-carb diets also decrease hunger, which could help with weight loss in the long term."
Ludwig and Ebbeling recently launched another clinical trial called FB4, in which 125 adults with obesity live in a residential center for 13 weeks. Participants are being randomized to one of three diets: very-low-carb, high carb/low sugar or high carb/high sugar diets, with their calorie intakes individually matched to their energy expenditure. Results are expected in 2021.
https://www.sciencedaily.com/releases/2018/11/181114120302.htm
How many calories do you burn? It depends on time of day
November 8, 2018
Science Daily/Cell Press
Researchers have made the surprising discovery that the number of calories people burn while at rest changes with the time of day. When at rest, people burn 10 percent more calories in the late afternoon and early evening than in the early morning hours.
The findings reinforce the important role of the circadian clock in governing metabolism. They also help to explain why irregularities in eating and sleeping schedules due to shift work or other factors may make people more likely to gain weight.
"The fact that doing the same thing at one time of day burned so many more calories than doing the same thing at a different time of day surprised us," says Kirsi-Marja Zitting of the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital and Harvard Medical School, lead author of the paper.
To determine changes over the course of the day in metabolism apart from the effects of activity, sleep-wake cycle, and diet, the researchers studied seven people in a special laboratory without any clues about what time it was outside. There were no clocks, windows, phones, or Internet. Study participants had assigned times to go to bed and wake up. Each night, those times were adjusted four hours later, the equivalent of traveling westward across four time zones each day for three weeks.
"Because they were doing the equivalent of circling the globe every week, their body's internal clock could not keep up, and so it oscillated at its own pace," co-author Jeanne Duffy, also in the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital, explains. "This allowed us to measure metabolic rate at all different biological times of day."
The data showed that resting energy expenditure is lowest at the circadian phase the researchers designated as ~0°, corresponding to the dip in core body temperature in the late biological night. Energy expenditure was highest at circadian phase ~180°, about 12 hours later, in the biological afternoon into evening.
The researchers found that participants' respiratory quotient, which reflects macronutrient utilization, varies by circadian phase, too. This measure was lowest in the evening and highest in the biological morning.
The findings offer the first characterization of a circadian profile in fasted resting energy expenditure and fasted respiratory quotient, decoupled from effects of activity, sleep-wake cycle, and diet in humans, the researchers say.
"It is not only what we eat, but when we eat -- and rest -- that impacts how much energy we burn or store as fat," Duffy says. "Regularity of habits such as eating and sleeping is very important to overall health."
Duffy, Zitting, and their colleagues next will look at how appetite and the body's response to food varies with the time of day. They are also exploring how the timing, duration, and regularity of sleep influences those responses.
https://www.sciencedaily.com/releases/2018/11/181108142423.htm
Athletes can rest easy: Extreme exercise does not raise heart disease risk or mortality
January 30, 2019
Science Daily/UT Southwestern Medical Center
High volumes of exercise are safe, even when coronary calcium levels are high, new research suggests.
Exercise is often cited as the best preventive medicine, but how much is too much for the hearts of middle-aged athletes?
Sports cardiologist Dr. Benjamin Levine led a study, now published in JAMA Cardiology, to find the answer. Dr. Levine is a Professor of Internal Medicine and Director of the Institute for Exercise and Environmental Medicine, a collaboration between UT Southwestern Medical Center and Texas Health Presbyterian Hospital Dallas.
What is coronary calcium scanning and why is it important?
Coronary calcium scanning is an imaging test that helps physicians classify patients without cardiac symptoms as low, intermediate, or high risk for heart attack. It represents how much calcium (and thus cholesterol deposits) has accumulated in the blood vessels that supply the heart. The scan can help physicians determine the need for medication, lifestyle modification, and other risk-reducing measures. Learn more
"The question has never been whether exercise is good for you, but whether extreme exercise is bad for you. For the past decade or so, there's been increasing concern that high-volume, high-intensity exercise could injure the heart. We found that high volumes of exercise are safe, even when coronary calcium levels are high," Dr. Levine said.
High-volume, high-intensity exercise was defined in this study as at least five to six hours per week at a pace of 10 minutes per mile. The average amount of high-intensity exercise in this group was eight hours per week.
Coronary calcium is a footprint of atherosclerosis, a disease in which plaque builds up in the arteries and gives rise to heart attack and stroke. When coronary calcium is detected in the heart, the clogging process within the blood vessels has begun. The majority of high-intensity athletes had low levels of coronary calcium, though their odds of having higher levels were 11 percent greater than men who exercised less. Most importantly, the researchers found that higher calcium scores did not raise the high-intensity athletes' risk for cardiovascular or all-cause mortality.
Dr. Levine studied data from the Cooper Center Longitudinal Study. A total of 21,758 generally healthy men ages 40 to 80 and without cardiovascular disease were followed for mortality between 1998 and 2013. The athletes, a majority of them in middle age, reported their physical activity levels and underwent coronary calcium scanning. Most were predominantly runners, but some were cyclists, swimmers, or rowers. A subgroup of athletes trained in three of these sports.
Women were not included in the study as their mortality rates are lower than for men.
Despite the findings that extreme exercise does not raise heart disease risk, Dr. Levine advises against using the protective effect of exercise to excuse poor lifestyle habits. "You cannot overcome a lifetime of bad behaviors -- smoking, high cholesterol, hypertension -- just from doing high levels of physical activity, so don't use that as a magical cure," said Dr. Levine, who holds the Distinguished Professorship in Exercise Sciences at UT Southwestern.
He also recommends caution when starting a new training program. "If you want to train for a marathon, you have to have a long-range plan to build up slowly before you achieve those volumes and intensity of exercise."
"The known benefits of regular physical activity in the general population include decreased mortality, heart disease, diabetes, and many other medical conditions which reminds us how important it is participate in regular physical activity as recommended by the 2018 Physical Activity Guidelines," said Dr. Laura DeFina, Chief Scientific Officer of The Cooper Institute and co-author of the study. "The current study shows no increased risk of mortality in high-volume exercisers who have coronary artery calcium. Certainly, these high-volume exercisers should review their cardiovascular disease risk with their primary care doctor or cardiologists and the study results provide helpful clinical guidance."
"The most important take-home message for the exercising public is that high volumes of exercise are safe. The benefits of exercise far outweigh the minor risk of having a little more coronary calcium," Dr. Levine said.
https://www.sciencedaily.com/releases/2019/01/190130175607.htm