Job Stress in Teachers Linked to Student Achievement
May 25, 2011
Science Daily/University of Houston
After 17 years of researching traumatic stress with war-afflicted populations (veterans and civilians) and job stress in the medical profession, Teresa McIntyre, a research professor in the department of psychology and the Texas Institute for Evaluation, Measurement and Statistics (TIMES), at the University of Houston (UH), decided to study another high risk occupation, middle school teachers in seventh and eighth grade.
"Middle school is probably the most difficult level to teach because student-teacher interactions are more difficult during this time, and this kind of difficulty in teacher-student interactions is a major source of stress for teachers at this level," McIntyre said.
"For students it's a time of adolescence and many changes developmentally, and that is going to affect the dynamics of learning, as well as the social relationships and climate in the classroom. It's going to affect the teachers as well. Our premise is that if the teacher is stressed, their behavior will be different with students, and they will perform differently with students."
http://www.sciencedaily.com/releases/2011/05/110525181422.htm
Pace of Brain Development Still Strong in Late Teens
May 10, 2011
Science Daily/Brown University
The brain changes during the teen years, for instance by pruning away connections that no longer seem needed. By measuring the brainwave signals of sleeping teens ages 15-16 and again a few years later, researchers found that the process does not appear to slow as teens approach adulthood.
Boys and girls have put many of the trappings of teenagerhood behind them by the age of 18 or 19, but at least some of the brain resculpting that characterizes the decade of adolescence may still be going as strong as ever, according to findings in a new study that measured brainwaves of subjects in their midteens and again in their late teens.
"The unique feature of this study is that it puts together these EEG measures of power and looks at these sleep stages longitudinally (in the same people over time) and across several regions around the brain," she said.
Carskadon said that sleep is a convenient time to take long-term, well controlled measurements of neural activity, but that the study does not show the role sleep may play in neural renovation among older teenagers.
http://www.sciencedaily.com/releases/2011/05/110510101621.htm
Teen Sleep Study Adds to Evidence of a 'Neural Fingerprint'
May 2, 2011
Science Daily/Brown University
New research finds that consistent, "signature" brainwave patterns first noticed in short-term studies of adults are so robust that they're also detectable over a matter of years in the notoriously turbulent brains of teens. From there, the question is what such a "neural fingerprint" might mean.
Teens are rarely described as stable, so when something about their rapidly changing brains remains placidly unaltered, neuroscientists take notice. Such is the case in a new study of electroencephalography (EEG) readings gathered from dozens of teens while they slept. Despite the major neural overhaul underway during adolescence, most individuals maintained a unique and consistent pattern of underlying brain oscillations. The work lends a new level of support to the idea, already observed in adults, that people produce a kind of brainwave "fingerprint."
"At the moment it's too soon to tell anything about individual sleep or behavior from this, but it could provide a tool to geneticists," she said. "It is a link between behavior and genes."
With further research, the functional or physiological significance of the patterns could become clearer, Carskadon said. One question would be whether particular influences such as sleep deprivation or alcohol use affect the pattern.
"Knowing this gives us another tool to examine brain function and stability," Carskadon said. "Showing that there are these fingerprints may open up future possibilities in using this kind of analysis in larger samples to look for endophenotypes that might be predictive of someone, say, who might go on to develop schizophrenia or depression."
http://www.sciencedaily.com/releases/2011/04/110426185251.htm
Caffeine Negatively Affects Children: Most Consume Caffeine Daily
December 17, 2010
Science Daily/Elsevier Health Sciences
Caffeine consumption in children is often blamed for sleep problems and bedwetting. Information on childhood caffeine consumption is limited, and many parents may not know the amount or effects of their child's caffeine consumption. In a study published in The Journal of Pediatrics, researchers found that 75% of children surveyed consumed caffeine on a daily basis, and the more caffeine the children consumed, the less they slept.
Dr. William Warzak and colleagues from the University of Nebraska Medical Center surveyed the parents of over 200 children 5 to 12 years old during routine clinical visits at an urban pediatric clinic. Parents were asked to report the types and amounts of snacks and beverages their child consumed on a daily basis.
According to Dr. Warzak, "Some children as young as 5 years old were consuming the equivalent of a can of soda a day." The authors also noticed that the older children drank more caffeinated beverages. "Children between the ages of 8 and 12 years consumed an average of 109 mg a day," Dr. Warzak explains, "the equivalent of almost 3 12-ounce cans of soda."
The study authors stress the importance of parental awareness regarding their child's caffeine consumption. "Parents should be aware of the potentially negative influence of caffeine on a child's sleep quality and daily functioning,"
http://www.sciencedaily.com/releases/2010/12/101216073209.htm
Exposure to early evening sunlight in spring creates teenage night owls
July 26, 2010
Science Daily/Rensselaer Polytechnic Institute
In the spring, later sunset and extended daylight exposure delay bedtimes in teenagers, according to new research.
"Biologically, this increased exposure to early evening light in the spring delays the onset of nocturnal melatonin, a hormone that indicates to the body when it's nighttime," explains Mariana Figueiro, Ph.D., associate professor. "This extended exposure adds to the difficulties teens have falling asleep at a reasonable hour."
Over time when coupled with having to rise early for school, this delay in sleep onset may lead to teen sleep deprivation and mood changes, and increase risk of obesity and perhaps under-performance in school, according to Figueiro.
"This is a double-barreled problem for teenagers and their parents," says Figueiro. "In addition to the exposure to more evening daylight, many teens also contend with not getting enough morning light to stimulate the body's biological system, also delaying teens' bedtimes."
Measuring "Circadian Light"
In the study, the Algonquin Middle School students were exposed to significantly more "circadian light" in the early evening during spring than in winter, resulting in both delayed melatonin onset and shorter self-reported sleep durations. Each subject wore a Daysimeter, a small, head-mounted device developed by the LRC to measure an individual's exposure to daily "circadian light," as well as rest and activity patterns. The definition of circadian light is based upon the potential for light to suppress melatonin synthesis at night, as opposed to measuring light in terms of how it stimulates the visual system.
This study, sponsored by the U.S. Green Building Council (USGBC) and, in part, by a grant from a Trans-National Institutes of Health Genes, Environment and Health Initiative (NIH-GEI), is the first to relate field measurements of circadian light exposures to a well-established circadian marker (the rise in evening melatonin levels) during two seasons of the year.
In a previous field study, also funded by USGBC and NIH-GEI and published in Neuroendocrinology Letters, Figueiro and Rea examined the impact of morning light on teen sleep habits and found that removing short-wavelength (blue) morning light resulted in a 30-minute delay in sleep onset by the end of a five-day period.
http://www.sciencedaily.com/releases/2010/07/100726124420.htm
Lack of morning light keeping teenagers up at night
February 27, 2010
Science Daily/Rensselaer Polytechnic Institute
The first field study on the impact of light on teenagers' sleeping habits finds that insufficient daily morning light exposure contributes to teenagers not getting enough sleep.
"As teenagers spend more time indoors, they miss out on essential morning light needed to stimulate the body's 24-hour biological system, which regulates the sleep/wake cycle," reports Mariana Figueiro, Ph.D., Assistant Professor and Program Director at Rensselaer Polytechnic Institute's Lighting Research Center (LRC) and lead researcher on the new study.
"These morning-light-deprived teenagers are going to bed later, getting less sleep and possibly under-performing on standardized tests. We are starting to call this the teenage night owl syndrome."
Disrupting Biological Rhythms
The problem is that today's middle and high schools have rigid schedules requiring teenagers to be in school very early in the morning. These students are likely to miss the morning light because they are often traveling to and arriving at school before the sun is up or as it's just rising. "This disrupts the connection between daily biological rhythms, called circadian rhythms, and the earth's natural 24-hour light/dark cycle," explains Dr. Figueiro.
In addition, the schools are not likely providing adequate electric light or daylight to stimulate this biological or circadian system, which regulates body temperature, alertness, appetite, hormones and sleep patterns. Our biological system responds to light much differently than our visual system. It is much more sensitive to blue light. Therefore, having enough light in the classroom to read and study does not guarantee that there is sufficient light to stimulate our biological system.
"According to our study, however, the situation in schools can be changed rapidly by the conscious delivery of daylight, which is saturated with short-wavelength, or blue, light," reports Dr. Figueiro.
The new research has applications for more than 3 million shift workers and Alzheimer's patients who suffer from lack of a regular sleep pattern.
Studies have shown that this lack of synchronization between a shift worker's rest and activity and light/dark patterns leads to a much higher risk of cardiovascular disease, diabetes, seasonal depression and cancer over decades.
As evidenced in prior studies by Dr. Figueiro, light therapy can also be used to improve sleep in Alzheimer's patients, who usually display uneven sleep patterns. "By removing light at certain times of day, and giving light at other times, you can synchronize the sleep/wake patterns of Alzheimer's patients with the light/dark pattern, providing them with more consolidated sleep," says Dr. Figueiro.
http://www.sciencedaily.com/releases/2010/02/100216140305.htm
Less Is More: Teens Who Sleep Less Eat More Fatty Foods and Snacks
September 7, 2010
Science Daily/American Academy of Sleep Medicine
A study in the Sept. 1 issue of the journal Sleep shows that teens who slept less than eight hours per weeknight ate higher proportions of fatty foods and snacks than adolescents who slept eight hours or more. The results suggest that short sleep duration may increase obesity risk by causing small changes in eating patterns that cumulatively alter energy balance, especially in girls.
Results show that a shorter mean weekday sleep duration was significantly associated with an increase in the percentage of calories consumed from fats and a decrease in the percentage of calories from carbohydrates. After adjusting for potential confounders such as age, sex and race, teens who slept less than eight hours on weeknights consumed 2.2 percent more calories from fats and 3.0 percent fewer calories from carbs than teens who slept eight hours or more. Further adjustments for body mass index (BMI) had little effect on these associations. In secondary analyses stratified by sex, the results were significant among girls but not boys.
"The relative increase in fat consumption among shorter sleepers by 2.2 percent per day chronically may contribute to cumulative increases in energy consumption that would be expected to increase risk for obesity and cardiovascular disease," said senior author and principal investigator Susan Redline, MD, MPH, professor of medicine in the Division of Sleep Medicine at Brigham and Women's Hospital and Beth Israel Deaconess Medical Center, teaching affiliates of Harvard Medical School in Boston, Mass.
"The demonstration of chronically altered dietary patterns in adolescents with shorter sleep provides insight into why shorter sleep has been associated with obesity in prior experimental and observational studies."
The study also found a relationship between sleep duration and snacking. For each one-hour increase in sleep duration, the odds of consuming a high amount of calories from snacks decreased by an average of 21 percent. Analyses of sleep duration and timing of nutrient intake revealed that a significantly greater proportion of teens who slept less than eight hours per weeknight consumed food in the early morning between 5 a.m. and 7 a.m.
"Altered timing of eating in shorter sleepers also may be a metabolic stress that contributes to metabolic dysfunction," said Redline.
http://www.sciencedaily.com/releases/2010/09/100901072854.htm
Faulty Body Clock May Make Kids Bipolar
November 13, 2009
Science Daily/BioMed Central
Malfunctioning circadian clock genes may be responsible for bipolar disorder in children. Researchers writing in the open access journal BMC Psychiatry found four versions of the regulatory gene RORB that were associated with pediatric bipolar disorder.
Alexander Niculescu from Indiana University School of Medicine, Indianapolis, US, worked with a team of researchers at Harvard, UC San Diego, Massachusetts General Hospital and SUNY Upstate Medical University to study the RORA and RORB genes of 152 children with the condition and 140 control children.
They found four alterations to the RORB gene that were positively associated with being bipolar. Niculescu said, "Our findings suggest that clock genes in general and RORB in particular may be important candidates for further investigation in the search for the molecular basis of bipolar disorder".
http://www.sciencedaily.com/releases/2009/11/091111200213.htm
Sleep Patterns In Children And Teenagers Could Indicate Risk For Depression
August 14, 2009
Science Daily/UT Southwestern Medical Center
Sleep patterns can help predict which adolescents might be at greatest risk for developing depression, a researcher at UT Southwestern Medical Center has found in a five-year study.
Sleep is a biological factor known to be associated with adult depression. Depressed adults experience rapid-eye-movement (REM) sleep earlier in the sleep cycle than people who are not depressed. Until this study, available online and in the July edition of Neuropsychopharmacology, it had been unclear whether this relationship held true in adolescents.
At the start of the study involving 96 adolescents with no evidence of depression or other psychiatric disorders, researchers monitored the sleep cycles of participants for three days and collected saliva and urine samples to record cortisol levels. The teens were then monitored for up to five years.
In addition to the sleep finding, researchers found that at the end of the five-year study period, adolescents with higher cortisol levels were more likely than others to develop depression.
"Depression is not mediated by sleep alone," Dr. Rao said. "If we can identify factors such as sleep and cortisol and their role, we could start the prevention process before the disease leads children and teenagers down a path well behind their peers educationally and socially."
http://www.sciencedaily.com/releases/2009/08/090813083335.htm
Better Sleep is Associated with Improved Academic Success
June 15, 2009
Science Daily/American Academy of Sleep Medicine
Getting more high-quality sleep is associated with better academic performance, according to a research abstract that will be presented on Wednesday, June 10, at SLEEP 2009, the 23rd Annual Meeting of the Associated Professional Sleep Societies. The positive relationship is especially relevant to performance in math.
Results indicate that higher math scores were related to greater sleep quality, less awakenings and increased sleep efficiency. Higher English and history scores were associated with less difficulty awakening. Increased sleep-onset latency over the weekend was associated with worse academic performance.
http://www.sciencedaily.com/releases/2009/06/090610091232.htm
Being A Night Owl in High School is Linked with Lower College GPA
June 11, 2009
Science Daily/American Academy of Sleep Medicine
According to a research abstract that will be presented on June 9, at Sleep 2009, the 23rd Annual Meeting of the Associated Professional Sleep Societies, students who consider themselves to be evening types (that is someone who feels more alert and does their best work later in the day) have poorer sleep hygiene scores than morning and intermediate types.
Sleep hygiene is the group of behaviors linked to good sleep and alertness. Examples include having a regular bedtime routine, a regular wake time, a regular bed time, and sleeping in a comfortable bed.
The researchers found that this poor sleep hygiene was related to poorer academic performance and a decline in grade point average (GPA) during the transition from high school to college.
http://www.sciencedaily.com/releases/2009/06/090609072813.htm
ADHD Linked to Sleep Problems in Adolescents
May 6, 2009
Science Daily/American Academy of Sleep Medicine
A new study shows that adolescents with a childhood diagnosis of Attention Deficit/Hyperactivity Disorder (ADHD) are more likely to have current and lifetime sleep problems and disorders, regardless of the severity of current ADHD symptoms. Authors suggest that findings indicate that mental health professionals should screen for sleep problems and psychiatric comorbidities among all adolescents with a childhood diagnosis of ADHD.
Results indicate that adolescents with a childhood diagnosis of ADHD, regardless of persistent ADHD were more likely to have current sleep problems and sleep disorders such as insomnia, sleep terrors, nightmares, bruxism and snoring. Of the total sample, 17 percent of children with ADHD were currently suffering from primary insomnia, versus 7 percent of controls; lifetime primary insomnia occurred in 20 percent of children with ADHD, compared to 10 percent of controls.
Nightmare disorder affected 11 percent of children with ADHD and lifetime nightmare disorder affected 23 percent, versus 5 and 16 percent of controls. The presence of at least one psychiatric comorbid condition increases the risks for insomnia and nightmares.
http://www.sciencedaily.com/releases/2009/05/090501090914.htm
Inadequate Sleep Leads to Behavioral Problems
April 28, 2009
Science Daily/University of Helsinki
A recent Finnish study suggests that children's short sleep duration even without sleeping difficulties increases the risk for behavioral symptoms of ADHD.
"We were able to show that short sleep duration and sleeping difficulties are related to behavioral symptoms of ADHD, and we also showed that short sleep, per se, increases behavioral symptoms, regardless of the presence of sleeping difficulties", says researcher Juulia Paavonen, MD, PhD.
"The findings suggest that maintaining adequate sleep schedules among children is likely to be important in preventing behavioral symptoms. However, even though inadequate sleep seems to owe potential to impair behaviour and performance, intervention studies are needed to confirm the causality," Paavonen continues.
http://www.sciencedaily.com/releases/2009/04/090427131313.htm
Brain Wave Patterns Can Predict Blunders
March 25, 2009
Science Daily/University of California - Davis
Everyone makes an occasional error due to lack of attention. Now scientists have found a distinct electric signature in the brain which predicts that such an error is about to be made. The discovery could prove useful in a variety of applications, from developing monitoring devices that alert air traffic control operators that their attention is flagging, to devising and monitoring new strategies to help children cope with attention deficit hyperactivity disorder.
"The alpha and mu rhythms are what happen when the brain runs on idle," Mazaheri explained. "Say you're sitting in a room and you close your eyes. That causes a huge alpha rhythm to rev up in the back of your head. But the second you open your eyes, it drops dramatically, because now you're looking at things and your neurons have visual input to process."
The team also found that errors triggered immediate changes in wave activity in the front region of the brain, which appeared to drive down alpha activity in the rear region, "It looks as if the brain is saying, 'Pay attention!' and then reducing the likelihood of another mistake," Mazaheri said.
It shouldn't take too many years to incorporate these findings into practical applications, Mazaheri said. For example, a wireless EEG could be deployed at an air traffic controller's station to trigger an alert when it senses that alpha activity is beginning to regularly exceed a certain level.
It could also provide new therapies for children with ADHD, he said. "Instead of watching behavior — which is an imprecise measure of attention — we can monitor these alpha waves, which tell us that attention is waning. And that can help us design therapies as well as evaluate the efficacy of various treatments, whether it's training or drugs."
http://www.sciencedaily.com/releases/2009/03/090323122439.htm
Underlying Sleep Problem Linked to ADD/ADHD Disorder In Children
March 2, 2009
Science Daily/American Academy of Sleep Medicine
A study in the March 1 issue of the journal SLEEP suggests the presence of an intrinsic sleep problem specific to attention-deficit/hyperactivity disorder (ADHD) and supports the idea that children with ADHD may be chronically sleep deprived and have abnormal REM sleep.
Results show that children with ADHD have a total sleep time that is significantly shorter than that of controls. Children in the ADHD group had an average total sleep time of eight hours, 19 minutes; this was 33 minutes less than the average sleep time of eight hours, 52 minutes, in controls. Children with ADHD also had an average rapid eye movement (REM) sleep time that was significantly reduced by 16 minutes.
According to the authors, this study may suggest that ADHD children suffer from an intrinsic sleep problem that could be related to the underlying pathophysiology of the disorder. They report that the impact of sleep duration on neuropsychological functioning in children with ADHD should be investigated further. Additional studies also will be required to examine whether shorter sleep duration in children with ADHD is associated with ADHD-like symptoms, including behavioral problems and poor neurocognitive functioning.
The authors suggest that if a functional alteration of sleep in children with ADHD can be confirmed, then it may be possible to develop therapeutic approaches for optimizing and individualizing the children's sleep regimes.
http://www.sciencedaily.com/releases/2009/03/090301094248.htm
Evening-Type College Students On Early Daytime Class Schedules At Disadvantage
June 10, 2008
Science Daily/American Academy of Sleep Medicine
Eveningness is associated with not only later phases of a person's sleep-wake cycle, but also with sleep irregularities, more pronounced sleep restriction during the week, and higher sleep compensation on weekends. Evening type college students may, therefore, need a sleep education that helps them adjust to imposed morning schedules, and would probably benefit from later class schedules, according to a research abstract that will be presented on June 10 at SLEEP 2008, the 22nd Annual Meeting of the Associated Professional Sleep Societies (APSS).
The results revealed that, more than other diurnal types, evening-oriented students show sleep debt during the week, sleep compensation on weekends, sleep-wake schedule irregularities, and later sleep-wake schedules. These results suggest a disagreement among their sleep-wake cycles and the morning class schedules.
"Our findings, together with other studies on the subject, lead us to firmly suspect that, at least in adolescents and young adults, evening-type students may face a real disadvantage when forced to adhere to morning classes," said Gomes.
http://www.sciencedaily.com/releases/2008/06/080610072044.htm
Poor Sleep May Increase Odds of Emotional, Behavioral Disturbances, ADHD
June 10, 2008
Science Daily/American Academy of Sleep Medicine
Insufficient sleep among adolescents may not only contribute to lower grades and a lack of motivation, but may also increase the odds of serious levels of emotional and behavioral disturbances, including ADHD, according to a research abstract that will be presented on June 9 at SLEEP 2008, the 22nd Annual Meeting of the Associated Professional Sleep Societies (APSS).
According to the results, students reported sleeping, on average, 7.6 hours per school night, with 48 percent reporting less than eight hours. Hours of sleep per school night were significantly positively associated with GPA and level of motivation, and significantly negatively associated with clinically significant levels of emotional disturbance and ADHD. Each additional hour of sleep on school nights lowered the odds of scoring in the clinically significant range of emotional disturbance and ADHD by 25 percent and 34 percent, respectively.
http://www.sciencedaily.com/releases/2008/06/080609071206.htm
College Student Sleep Patterns Could Be Detrimental
May 13, 2008
Science Daily/Central Michigan University
A Central Michigan University study has determined that many college students have sleep patterns that could have detrimental effects on their daily performance.
College students are among the most sleep-deprived age group in the U.S. Sleep deprivation can have detrimental effects on daily performance, including academics and driving, and has also been linked to depressed mood and behavioral problems.
A similar study by Forquer and Johnson, published in "Sleep and Hypnosis," found that the use of continuous white noise may help college students get better sleep. The study found that white noise was effective for college students with self-reported sleep problems to decrease difficulty in falling asleep and night wakings.
"These issues are extremely important because not getting enough sleep is associated with impaired attention, school performance, and also can lead to driving accidents as people fall asleep behind the wheel of their car," said Forquer. "Helping students sleep better will hopefully carry over to help them in some of these areas as well."
http://www.sciencedaily.com/releases/2008/05/080512145824.htm
Sleep Problems Common in Children With ADHD
April 8, 2008
Science Daily/JAMA and Archives Journals
Children with attention-deficit/hyperactivity disorder (ADHD) appear likely to experience sleep problems, according to a new report. Sleep problems in these children may be associated with poorer child psychosocial quality of life, child daily functioning, caregiver mental health and family functioning.
"ADHD is the most common mental health disorder in childhood, affecting up to 11 percent of Australians aged 6 to 17 years," according to background information in the article. About half of parents of children with ADHD report that their children have difficulty sleeping, feel tired on waking or have nightmares or other sleep problems such as disordered breathing and restless leg syndrome. Parents of children with ADHD are more likely to experience stress, anxiety and depression than those of children without ADHD.
Sleep problems affected 175 (73.3 percent) of the children, with a 28.5 percent prevalence of mild sleep problems and 44.8 percent prevalence of moderate or severe sleep problems. Some of the most commonly occurring sleep patterns were difficulty falling asleep, resisting going to bed and tiredness on waking.
"Compared with children without sleep problems, those with sleep problems were more likely to miss or be late for school, and their caregivers were more likely to be late for work," the authors write. "Forty-five percent of caregivers reported that their pediatricians had asked about their children's sleep and, of these, 60 percent reported receiving treatment advice."
"In summary, sleep problems in schoolchildren with ADHD are extremely common and strongly associated with poorer quality of life, daily functioning and school attendance in the child and poorer caregiver mental health and work attendance," the authors conclude. "Implementation of a sleep intervention in children with ADHD could feasibly improve outcomes beyond treatment of ADHD alone. It is possible that such intervention could reduce the need for medication in some children."
http://www.sciencedaily.com/releases/2008/04/080407160751.htm
Insomnia Linked to Depression in Young Adults
April 3, 2008
Science Daily/American Academy of Sleep Medicine
A new study confirms the persistent nature of insomnia and the increased risk of subsequent depression among individuals with insomnia.
According to the results, the annual prevalence of one-month insomnia increased gradually over time, with a cumulative prevalence rate of 20 percent and a greater than two-fold risk among women. In 40 percent of subjects, insomnia developed into more chronic forms over time. Insomnia either with or without comorbid depression was highly stable over time. Insomnia lasting two weeks or longer predicted major depressive episodes and major depressive disorder at subsequent interviews.
Seventeen to 50 percent of subjects with insomnia lasting two weeks or longer developed a major depressive episode reported in a later interview. "Pure" insomnia and "pure" depression were not longitudinally related to each other, whereas insomnia comorbid with depression was longitudinally related to both.
"We used to think that insomnia was most often just a symptom of depression. However, a growing body of evidence suggests that insomnia is not just a symptom of depression, but that it may actually precede depression. In other words, people who have insomnia but no depression are at increased risk for later developing depression. This study adds to our knowledge by including a much longer follow-up period than most previous studies," said Daniel J. Buysse, MD, of the University of Pittsburgh, lead author of the paper.
"We were also able to look separately at insomnia alone, depression alone, and combined insomnia-depression. The results show that insomnia seems to be followed by depression more consistently than the other way around. In addition, we found that insomnia tended to be a chronic problem that gets more persistent over time, whereas depression was a more intermittent problem."
http://www.sciencedaily.com/releases/2008/04/080401081937.htm