By Agencies

Research suggests disruptions to natural rhythm may cause decline in memory and attention span and affect mental health.

Messing with the rhythm of one's internal body clock and sleep cycle may increase the risk of developing mood problems ranging from depression to bipolar disorder, scientists have found.

The study, published in the Lancet Psychiatry journal on Tuesday, 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 time-keeper 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 Laura Lyall, a University of Glasgow psychologist, 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 after the potential impact of factors such as old age, unhealthy lifestyle, obesity and childhood trauma had been taken into account, the researchers said. 

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.