Low days are not broken days.

Chronic low mood (sometimes called dysthymia or persistent depressive disorder) sits below the threshold for major depression in intensity but above what most people consider normal fluctuation in mood. Key differences: major depression typically involves distinct episodes with clear onset and remission; chronic low mood is persistent (present most days for at least two years in the clinical definition) but less severe. Someone with chronic low mood often functions normally but feels like a grey filter is over everything. The distinction matters for treatment — chronic low mood often responds well to structured lifestyle intervention before medication is needed.

Low mood is not only triggered by external events. Persistent low mood can arise from accumulated sleep debt, chronic low-grade inflammation (linked to diet, sedentary behaviour, and stress), disrupted circadian rhythm, social isolation, or the absence of activities that produce a sense of meaning or mastery. When none of these are addressed, the mood system has no reason to shift upward. The absence of an obvious cause is not evidence that the low mood is irrational — it often means the cause is physiological and requires a lifestyle change, not a reason.

Seek professional assessment if: the mood has been present most days for more than two weeks, it is interfering with work, relationships, or basic self-care, it is accompanied by thoughts of self-harm or hopelessness, or it has not responded to consistent sleep, exercise, and social contact changes over four to six weeks. A GP can screen for thyroid dysfunction, vitamin D deficiency, and anaemia — all common physical causes of persistent low mood that respond quickly to treatment and are frequently overlooked.

Four practices have consistent evidence: (1) Exercise — 20 to 30 minutes of moderate aerobic exercise three times a week has effect sizes comparable to antidepressants in mild-to-moderate depression. (2) Sleep regulation — keeping a consistent wake time regardless of the previous night is the strongest single lever for mood in clinical sleep research. (3) Behavioural activation — scheduling small activities that produce a sense of accomplishment or pleasure, before you feel like it (waiting until you feel like it defeats the mechanism). (4) Sunlight exposure in the morning — 10 to 20 minutes within an hour of waking regulates cortisol and serotonin rhythms.