Why body clocks are moving up the bipolar disorder agenda

An international group of experts has reached agreement on a broad set of information about body clocks, sleep and light that clinicians may need when caring for people with bipolar disorder.

The study was an expert-consensus exercise, not a trial of treatment effectiveness. Its authors said the work was intended to help optimise care and strengthen training in chronobiology—the study of biological rhythms—and chronotherapy, which uses timing-related approaches in clinical care.

What the study examined

Crouse and colleagues brought together 30 experts from 15 countries across Europe, North and South America, and the Asia Pacific. Using a Delphi process, the panel reviewed statements drawn from research papers and grey literature.

The research team initially identified 960 statements. Experts rated 837 of them over three rounds. A statement was considered to have reached consensus when at least 80% of the panel rated it essential or important.

In total, 342 statements met that threshold. They were organised into four areas: basic circadian science; circadian health and disruption; the chronobiology of bipolar disorder; and chronotherapies.

Sleep, light and mood stability

The consensus statements describe biological rhythms as responsive to external cues. Light is one such cue, and the panel highlighted the roles of morning light and reduced evening light in helping keep the biological clock aligned and limiting social jetlag.

The study also distinguishes melatonin from the common description of it as a “sleep hormone.” The source describes melatonin as a chemical signal of darkness. It notes that light suppresses melatonin and that people can differ in their natural timing, with some tending towards “night owl” patterns and others towards “morning lark” patterns.

Within the bipolar-disorder-specific material, an irregular sleep-wake cycle was associated with mood instability. The relationship between sleep and bipolar disorder was described as bi-directional: sleep disturbances may contribute to bipolar symptoms, while bipolar disorder may contribute to sleep disturbances. The source also states that sleep problems can persist whether someone is experiencing an episode or not.

Six chronotherapy approaches

The chronotherapy section identified six major approaches:

• Bright light therapy
• Wake therapy
• Dark therapy
• Interpersonal and social rhythm therapy
• Cognitive behavioural therapy for insomnia adapted for bipolar disorder
• Melatonin and melatonergic agonists

The source states that practitioners with sufficient training and the appropriate equipment could intervene with the listed approaches. However, it specifically says the evidence remains insufficient to determine whether melatonin and melatonergic agonists work.

More broadly, the consensus process does not establish that any of these approaches improves mood stability or long-term outcomes. The authors presented those outcomes as a hope, not as something tested by this study.

A gap in education

The findings also point to a training gap. A previous review of 25 practice guidelines found that fewer than half discussed circadian disturbances. Separately, a survey of 409 medical schools in 12 countries reported that schools spent less than three hours on sleep education during medical training; one quarter did not address the topic at all.

The authors therefore called for greater inclusion of chronobiology and chronotherapy in medical education, particularly in psychiatric training. They also said that explaining these concepts to patients could support their participation in healthcare.

Why the findings need careful interpretation

The panel was recruited through snowball sampling, and the source notes that this may have contributed to the strong representation of areas linked to the International Society for Bipolar Disorders. There were no participants from Africa, China or India, and very few from countries with distinctive circadian conditions such as polar nights.

Psychiatric nurses and other non-psychiatrist medical professionals were also not prominent among participants. The source notes that some paper authors are known proponents of the chronotherapies discussed, creating a potential source of bias.

For these reasons, the authors suggest that countries not represented in the study should review and adapt the findings for local use rather than applying them without professional caution. The central message is one of education and clinical context: body-clock science may be important to bipolar-disorder care, but consensus about what clinicians should know is not the same as proof that every intervention is effective.

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