Study links body clock to mood disorders

Pregnancy naps linked with healthier birth weight

PARIS, May 16, (Agencies): Messing with the natural rhythm of one’s internal clock may boost the risk of developing mood problems ranging from garden-variety loneliness to severe depression and bipolar disorder, researchers said Wednesday.

The largest study of its kind, involving more than 91,000 people, also linked interference with the body’s “circadian rhythm” to a decline in cognitive functions such as memory and attention span.

The brain’s hard-wired circadian timekeeper governs day-night cycles, influencing sleep patterns, the release of hormones and even body temperature.

Earlier research had suggested that disrupting these rhythms can adversely affect mental health, but was inconclusive: most data was self-reported, participant groups were small, and potentially data-skewing factors were not ruled out.

For the new study, an international team led by University of Glasgow psychologist Laura Lyall analysed data — taken from the UK Biobank, one of the most complete long-term health surveys ever done — on 91,105 people aged 37 to 73.

The volunteers wore accelerometers that measured patterns of rest and activity and had this record compared to their mental history, also taken from the UK Biobank.

Individuals with a history of disrupting their body’s natural rhythm — working night shifts, for example, or suffering repeated jetlag — also tended to have a higher lifetime risk of mood disorders, feelings of unhappiness, and cognitive problems, the researchers found.

The results held true even when the potential impact of factors such as old age, unhealthy lifestyle, obesity, and childhood trauma were taken into account, they reported in The Lancet Psychiatry, a medical journal.

The study cannot say conclusively that body clock disturbances are what caused the mental risk, instead of the other way round.

But the findings “reinforce the idea that mood disorders are associated with disturbed circadian rhythms,” said Lyall.

Measurements of people’s restwork cycles could be a useful tool for flagging and treating people at risk of major depression or bipolar disorders, the researchers concluded.

One limitation of the study was the average age of the trial participants — 62.

“Seventy-five percent of [mental] disorders start before the age of 24 years,” said University of Oxford researcher Aiden Doherty, commenting on the paper.

“The circadian system undergoes developmental changes during adolescence, which is also a common time for the onset of mood disorders,” he added.

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Pregnant women who nap regularly may reduce their baby’s risk of low birth weight, a study from China suggests.

“Low birth weight is one of the feared outcomes of pregnancy, and novel insight into risk factors is welcome,” said Dr. Ghada Bourjeily, a sleep researcher at Brown University’s Warren Alpert Medical School in Providence, Rhode Island, who wasn’t involved in the study.

“Sleep, its quality, and duration are emerging as risk factors for various perinatal complications,” Bourjeily said in an email.

Low birth weight, defined as less than 5.5 pounds (2500 grams), is associated with adverse health outcomes in childhood and adulthood, including respiratory illnesses, diabetes and hypertension. In the US, about 8 percent of babies have low birth weight, according to the Centers for Disease Control and Prevention.

Lulu Song of the Huazhong University of Science and Technology in Wuhan and colleagues analyzed information from more than 10,000 women who were participating in the 2012-2014 Healthy Baby Cohort study in China. The group included 442 women who had low birth weight babies, the authors reported in the journal Sleep Medicine.

Compared to mothers who reported no napping, women who took naps of roughly an hour to an hour and a half were about 29 percent less likely to have a baby with low birth weight.

The frequency of napping also seemed to play a role: women who napped on five to seven days per week were 22 percent less likely to have a baby with low birth weight.

The study wasn’t a controlled experiment and so it can’t prove that pregnant mothers’ nap habits affect babies’ birth weight.

Still, the findings add “another piece of the puzzle as to why we should be aware about sleep practices during pregnancy,” said Dr Louise O’Brien of the University of Michigan Sleep Disorders Center in Ann Arbor, Michigan, who wasn’t involved in the study.

O’Brien, who researches sleep disruption during pregnancy and perinatal outcomes, told Reuters Health by email, “Many sleep behaviors are modifiable, and if napping is a risk for poor outcomes, then we need to understand why that is.”