Despite obtaining a full night’s sleep, many individuals continue to experience lethargy and low energy, prompting experts to explore less obvious factors contributing to daytime tiredness. Recent insights highlight a variety of lifestyle and physiological elements that may undermine restfulness and overall vitality.

One environmental factor is air quality in the bedroom. Dr. Jemma King, author and sleep specialist, explains that typical bedroom conditions by early morning can see carbon dioxide levels rise significantly—often between 1,500 and 2,500 parts per million—due to closed doors, windows, multiple occupants, and heating. Research indicates that when indoor CO2 exceeds 1,000 ppm, sleep efficiency declines, deep sleep diminishes, and cortisol levels heighten upon waking, leading to a state of mild nervous system activation throughout the night. Simply opening a window slightly can improve ventilation and potentially enhance sleep quality.

Metabolic factors also play a role. Adenosine triphosphate (ATP), a key energy molecule produced by mitochondria, decreases with age, which may contribute to feelings of fatigue. Justin Roberts, professor of nutritional physiology, notes that creatine supplementation can aid ATP regeneration, benefiting mental and physical energy levels. Studies have demonstrated that daily intake of 3-5 grams of micronised creatine monohydrate over several weeks can improve mood, cognitive function, and sleep quality, particularly following poor rest.

Exposure to natural daylight is another important factor impacting circadian rhythms, according to Dr. Brendan Gabriel of the University of Aberdeen. Daylight helps regulate the brain’s suprachiasmatic nucleus, a central component of the body’s internal clock, thereby supporting better sleep and glucose metabolism. Limited outdoor time can disrupt these processes and contribute to tiredness.

Dietary habits significantly influence energy levels. Dr. Emily Leeming, a research fellow at King’s College London, emphasizes that most people fail to meet the recommended daily fibre intake of 30 grams, which supports steady blood sugar levels and sustained energy. Increasing consumption of beans, greens, berries, grains, seeds, and nuts is advised. Additionally, sluggish bowel function can signal fatigue due to gut-brain communication via the vagus nerve; consuming two kiwis daily may alleviate this by softening stool and promoting gut motility.

Excessive protein intake at the expense of carbohydrates may also impair energy. Sports dietitian Kerri Major warns that inadequate carbohydrate consumption relative to activity levels can reduce energy availability. Balanced meals featuring half vegetables, a quarter carbohydrates, and a quarter protein, along with healthy fats, are recommended to maintain steady energy throughout the day.

Other factors impacting sleep and energy include allergens and hygiene. King notes that dust mite allergens, synthetic fibers, and fragranced laundry products found in bedding may provoke low-level inflammation, resulting in disrupted sleep. Regular washing with fragrance-free detergent, using dust mite covers, and airing bedding each morning may mitigate these effects.

Behavioral factors such as prolonged sitting have evolutionary implications for fatigue. King suggests that extended sedentary periods signal the body to conserve energy through increased sleepiness and social withdrawal, a possible mechanism rooted in ancestral illness responses. Interrupting sitting every 30 minutes with brief movement or a short walk after meals can improve energy and glucose regulation.

Finally, underlying health conditions should be considered. Dr. Linia Patel, dietitian and author, advises that iron or vitamin B12 deficiency and thyroid disorders often cause chronic fatigue despite adequate rest. Symptoms range from physical exhaustion and breathlessness to neurological impairments and mood changes. Individuals experiencing persistent tiredness are encouraged to seek blood tests to rule out these conditions.

Meal timing also affects sleep quality. Eating large, protein-heavy meals late in the evening can disrupt the body’s nocturnal cooling process necessary for deep sleep. King recommends finishing dinner by 7:30 p.m. and favoring lighter proteins, vegetables, and plant-based carbohydrates in the evening to promote better rest and energy the following day.