Out of the blue? How the colour of light could be used to treat mental illness | Medical research

At first glance, the psychiatric ward in Trondheim looks much like any other unit caring for patients in acute mental distress. But as evening falls, filters descend over the windows, and the lights shift to a soft amber glow. By removing blue wavelengths that interfere with the body’s internal clock, doctors here are testing an unusual idea: that the design of the ward itself could become a form of treatment.

Light is the main signal regulating the body’s circadian rhythm – the roughly 24-hour biological clock that governs sleep and many other bodily processes. Mounting evidence links circadian disruption to conditions including depression, cardiovascular disease and dementia, and disturbed sleep-wake cycles are a long-recognised feature of mental illness, particularly bipolar disorder.

“Increasingly, both anecdotal and experimental evidence suggests that bipolar people are quite sensitive to light, which can be unhelpful for them in terms of seasonal changes in mood and more manic relapses with the lengthening days in springtime,” said Prof Daniel Smith, a psychiatrist at the University of Edinburgh who leads the UK Circadian Mental Health Network and was not involved in the study.

“The general idea is that evening light exposure, in particular, delays the phase of the clock, suppresses melatonin, and because of that, people go to sleep later and probably don’t sleep as well,” he said. Poor sleep can then destabilise daily patterns of rest and activity, which in vulnerable individuals may trigger mood episodes.

Because of this, there is growing interest in using light to stabilise people’s body rhythms and, in turn, improve their symptoms – although relatively few large clinical studies have tested the idea.

When doctors in Trondheim began planning a new psychiatric unit, it offered a rare chance to test the idea in practice. The team installed a dynamic lighting system and automated blinds designed to remove blue wavelengths from the ward in the evening.

“Many patients with severe mental illness have circadian disruption, and we wanted to see whether we could do something about this by changing the light system,” said Håvard Kallestad, a researcher and consultant psychologist at St Olavs hospital and the Norwegian University of Science and Technology, who led the research.

The unit was divided into two identical halves with the same layout, staffing and facilities. The only difference was the evening light environment. In one ward, lighting shifts from 6pm to remove blue wavelengths – the type the circadian system is most sensitive to – while blinds and filters block similar light from windows and screens. In the other, patients experience standard hospital lighting.

An earlier study showed that healthy volunteers staying in the ward experienced changes in melatonin secretion, sleep patterns and alertness.

The team have now tested the approach in 476 patients admitted for short-term psychiatric intensive care with conditions including psychosis, mania, severe depression and suicidal thoughts. Half were assigned to the ward with blue-depleted lighting and half to standard lighting.

The research, presented at a recent meeting of the International Society for Bipolar Disorders and published in PLOS Medicine, found that although the overall length of stay was similar – typically three or four days – patients treated in the circadian-adapted ward showed greater clinical improvement and less aggressive behaviour.

Kallestad said: “We saw that there was an additional gain from being in this blue-light environment in terms of how many patients were in a mild disease state at discharge, and the level of improvement that patients had during their admission.

“Just by changing the light spectrum, we can improve the quality of treatment, and we saw that in particular on aggressive behaviour.”

Aggression and agitation are common challenges in acute psychiatric wards, where studies suggest the occurrence of aggressive behaviour ranges between 8% and 76% of cases, posing risks for both patients and staff.

Smith said: “I think the aggression finding alone is really important, because it makes looking after these people just that little bit easier.”

Prof Derk-Jan Dijk, a sleep and circadian rhythm researcher at the University of Surrey, who was not involved in the study, said one of its most interesting aspects was that the intervention was built into the ward itself. “The burden to the participants is essentially zero – they don’t have to sit in front of a light box or wear blue-blocking glasses.”

Such approaches could be implemented at scale by designing indoor environments that align better with human biology, he added. “They confirm that the effects of light on the brain are not limited to the biological clock or sleep. They also influence mood and alertness.”

Researchers are also exploring whether circadian lighting could benefit people beyond psychiatric wards. The UK’s National Institute for Health and Care Research has launched a funding call for trials testing whether it could help “reset” the internal clocks of people living in care homes and reduce behavioural disturbances in dementia.

Prof Anthony Gordon, director of NIHR’s health technology assessment programme, said: “It’s about determining if we can use light therapy to reduce anxiety, improve sleep, and provide a cost-effective, drug-free way to enhance the quality of life in residential care across the country.”

Prof Colleen McClung, a neuroscientist at the University of Pittsburgh who published a review on circadian rhythms in psychiatric disorders last month, said such approaches may become increasingly personalised: “For example, if someone has circadian rhythms that are delayed, light therapy in the morning will shift rhythms forward. If someone’s rhythms are advanced, light therapy in the afternoon or evening could be beneficial.”

Wearable devices that track sleep and activity patterns could help identify these individual differences and guide treatment, she said.