Fatigue is the most common symptom presenting to general practitioners in the UK, accounting for up to 20 percent of consultations. It is also one of the most frequently dismissed, often attributed to lifestyle factors and managed with lifestyle advice that does not engage with the underlying physiology. Persistent fatigue that does not resolve with rest warrants systematic investigation. A single cause is unusual: most cases involve multiple overlapping factors that interact and amplify each other. Addressing one without the others produces partial improvement at best.
The Physiological Causes: Rule These Out First
The first step is ruling out medical causes that are both common and treatable. Iron deficiency anaemia is the most prevalent nutritional deficiency in UK women, producing fatigue through reduced oxygen-carrying capacity. Thyroid dysfunction, both hypothyroidism and subclinical hypothyroidism, produces fatigue, cognitive slowing, and low motivation through its effects on cellular metabolism. Vitamin D deficiency, vitamin B12 deficiency, and low magnesium are all common and all produce fatigue through distinct mechanisms. Type 2 diabetes and prediabetes produce energy dysregulation through insulin resistance and glycaemic variability. A basic blood panel covering all of these costs little and eliminates significant causes before lifestyle interventions are pursued.
Sleep Quality Versus Sleep Quantity
Many adults sleeping the recommended seven to nine hours still feel unrefreshed. The distinction between sleep quantity and sleep quality is critical. Sleep apnoea, which affects an estimated 10 percent of UK adults and the majority of those remain undiagnosed, produces multiple arousals per night without conscious waking, eliminating restorative slow-wave and REM sleep. Markers of sleep apnoea include loud snoring, morning headache, waking unrefreshed regardless of duration, and daytime sleepiness. A home sleep study can be arranged privately for modest cost.
The HPA Axis and Burnout
Chronic psychological stress, occupational burnout, and sustained high demands on the HPA axis produce a pattern of fatigue that is distinct from simple sleep deprivation or nutritional deficiency. Dysregulation of the cortisol awakening response, normally a sharp cortisol spike in the first 30 to 60 minutes after waking that provides morning energy, is measurable in adults with burnout. Cortisol either spikes too little, leaving morning fatigue, or too much, producing anxiety. This pattern is addressed differently from other fatigue causes and requires nervous system regulation alongside the other interventions.
- Request a blood panel covering: FBC, ferritin, thyroid function, 25-hydroxyvitamin D, B12, folate, fasting glucose, and HbA1c
- Address sleep quality before sleep quantity: if snoring is present, investigate for sleep apnoea
- Rule out dehydration: increase fluid intake to 35ml per kilogram body weight per day for two weeks and track energy
- Address the HPA axis if chronically stressed: slow breathing, regular moderate exercise, and social support all reduce cortisol dysregulation
- Eliminate alcohol: even moderate regular consumption impairs sleep architecture and produces next-day energy deficits significantly larger than most people realise
Sources
- Cullen, W., et al. (2002). Chronic fatigue in general practice: characteristics and management. British Journal of General Practice, 52(480), 554-558.
- Pawlikowski, M., et al. (2009). The prevalence of subclinical thyroid dysfunction in general medical practice. Endokrynologia Polska, 60(3), 180-186.