The Healthspan Map · Body system

General / Whole-body Energy

Conditions in this system

Chronic fatigue / low energy

Named for a condition in this system

Evidence naming a condition in General / Whole-body Energy — 57 sources.In the order the Map holds them: strongest evidence first. That is a statement about the evidence, not about what matters most.
Nutrient or lever	Direction	Strength	Evidence type	What was found	Source
Cardio (moderate + intervals)	Do this	Strong	RCT / meta-analysis	Physical activity moderately reduces fatigue overall (SMD 0.70); aerobic training is effective and consistently beats staying sedentary.	Physical activity & fatigue meta-analysis (38 RCTs, PMC10477297) (opens in a new tab)
Iron	Eat enough of	Strong	RCT / meta-analysis	Iron deficiency even without anaemia is a well-supported cause of fatigue (clearest in low-ferritin menstruating women and athletes); repletion improves it.	Iron-deficiency-without-anaemia & fatigue meta-analysis (Br J Nutr) (opens in a new tab)
Sleep duration	Watch this	Strong	Established clinical	Sleep deprivation is the single most common cause of daytime sleepiness and fatigue; symptoms appear after even mild sleep restriction.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Sleep quality (refreshed)	Watch this	Strong	Established clinical	Non-restorative, fragmented sleep (frequent unnoticed awakenings) leaves people unrefreshed and fatigued despite adequate hours in bed.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Strength (resistance)	Do this	Strong	RCT / meta-analysis	Resistance training showed the largest single-mode effect on fatigue (SMD 0.93).	Physical activity & fatigue meta-analysis (PMC10477297) (opens in a new tab)
Vitamin B12	Eat enough of	Strong	Established clinical	B12 is essential for oxygen transport and neuronal function; deficiency causes fatigue and macrocytic anaemia.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Added Sugars	Don't overdo	Moderate	Cohort / observational	High added-sugar loads produce larger post-meal glucose dips, predicting lower alertness and an energy crash.	Postprandial glucose-dip & alertness study (PREDICT) (opens in a new tab)
Alcohol — cut back	Do this	Moderate	Established clinical	Alcohol fragments sleep architecture and, as a sedating substance, contributes to next-day sleepiness and fatigue.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Anchor foods	Watch this	Moderate	Review / narrative	A nutrient-dense whole-food pattern protects against the undernutrition and inflammation that mediate fatigue.	Nutritional status & fatigue review (PMC7071235) (opens in a new tab)
BMI	Watch this	Moderate	Cohort / observational	Fatigue tracks BOTH extremes of body weight: obesity drives it via systemic inflammation (CRP/IL-6/TNF-a), and undernutrition/underweight cause fatigue in a vicious loop (too tired to prepare meals).	Nutritional status & fatigue review (PMC7071235) (opens in a new tab)
Blood oxygen (SpO2)	Watch this	Moderate	Cohort / observational	Low mean oxygen saturation and the oxygen-desaturation index predict excessive daytime sleepiness better than apnea count itself — nighttime hypoxia is a direct fatigue driver.	OSA daytime-sleepiness cohort (SESAR, n=34,684) (opens in a new tab)
Breath/mind (slow breathing)	Do this	Moderate	Review / narrative	Emotional exhaustion is the defining feature of burnout; chronic stress drives cortisol dysregulation, insomnia and chronic fatigue — stress-reduction is a direct lever.	Burnout review (PMC8834764) (opens in a new tab)
Caffeine — mind amount & timing	Do this	Moderate	Established clinical	Late-day caffeine erodes sleep quality and masks sleep debt, producing net next-day fatigue — timing matters more than amount.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Cardio / VO2max	Watch this	Moderate	RCT / meta-analysis	Higher aerobic capacity underlies lower fatigue; low fitness is itself a fatigue driver.	Physical activity & fatigue meta-analysis (PMC10477297) (opens in a new tab)
Daily movement baseline	Do this	Moderate	RCT / meta-analysis	Regular baseline movement reduces perceived fatigue; deconditioning worsens it.	Physical activity & fatigue meta-analysis (PMC10477297) (opens in a new tab)
Falling & staying asleep	Watch this	Moderate	Established clinical	Trouble initiating or maintaining sleep fragments the night and produces daytime tiredness.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Folate (B9)	Eat enough of	Moderate	Review / narrative	Folate supports DNA synthesis and red-cell formation; deficiency contributes to fatigue and anaemia.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Iron	Don't overdo	Moderate	Established clinical	Iron overload (hemochromatosis) commonly presents with fatigue — the both-sides flip of the iron story.	Iron overload / hemochromatosis symptoms (opens in a new tab)
Iron	Don't overdo	Moderate	Established clinical	Iron overload (hemochromatosis) commonly presents with fatigue — the both-sides flip of the iron story.	NIH Office of Dietary Supplements — Iron (opens in a new tab)
Loneliness — reduce	Watch this	Moderate	Cohort / observational	Loneliness predicted incident fatigue (adjusted OR 1.88) and the pain-fatigue-depression cluster (OR 3.16) over time.	Loneliness & symptom-cluster longitudinal study (HRS, n=11,766) (opens in a new tab)
Magnesium	Eat enough of	Moderate	Review / narrative	Magnesium is a cofactor in ATP-dependent energy metabolism; low status is linked to fatigue.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Morning daylight	Do this	Moderate	Cohort / observational	Bright morning light raises daytime vitality/alertness and improves next-morning energy by anchoring the circadian clock.	Morning bright-light & alertness field study (PubMed 36058557) (opens in a new tab)
Movement (breaking up sitting)	Do this	Moderate	RCT / meta-analysis	Interrupting prolonged sitting counters the deconditioning and fatigue of a sedentary day.	Physical activity & fatigue meta-analysis (PMC10477297) (opens in a new tab)
Protein	Eat enough of	Moderate	Review / narrative	Inadequate protein (below ~1.0-1.2 g/kg/day in older adults) accelerates muscle loss, sarcopenia and functional decline — a fatigue and frailty driver.	Protein/omega-3/vitD & muscle-function review (PMC6116139) (opens in a new tab)
Sleep regularity	Watch this	Moderate	Cohort / observational	Circadian misalignment blunts daytime alertness; realigning the sleep-wake schedule and light timing restores next-day energy.	Morning light & sleep/alertness field study (PubMed 36058557) (opens in a new tab)
Sugary drinks & snacks — cut back	Do this	Moderate	Cohort / observational	Large blood-sugar dips 2-3 h after high-glycemic meals predict lower alertness and greater hunger — the classic energy crash.	Postprandial glucose-dip & alertness study (PREDICT, n=1,070) (opens in a new tab)
Thiamin (B1)	Eat enough of	Moderate	Review / narrative	Thiamin is central to carbohydrate energy metabolism; deficiency causes fatigue and weakness.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Tobacco / vaping — quit	Do this	Moderate	Cohort / observational	Smokers show more insomnia, poor sleep quality, shorter sleep and daytime drowsiness; carbon monoxide also lowers oxygen delivery.	Smoking & sleep population study (WHO MONICA) (opens in a new tab)
Toxic relationships — reduce	Watch this	Moderate	Cohort / observational	Chronic interpersonal stress feeds the same psychosocial-stress pathway that drives fatigue, pain and low mood.	Loneliness/psychosocial-stress & fatigue study (HRS) (opens in a new tab)
Ultra-processed food — cut back	Do this	Moderate	Review / narrative	Poor diet quality contributes to the micronutrient gaps and inflammation that underlie fatigue.	Nutritional status & fatigue review (PMC7071235) (opens in a new tab)
Vitamin C	Eat enough of	Moderate	Review / narrative	Vitamin C supports carnitine synthesis and energy metabolism; early deficiency presents as fatigue.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Vitamin D	Eat enough of	Moderate	RCT / trial	In deficient adults, vitamin D3 significantly improved fatigue vs placebo (mild effect) — a deficiency-context lever, not a universal energy booster.	Vitamin D & self-perceived fatigue RCT (Nowak 2016) (opens in a new tab)
Water	Eat enough of	Moderate	Cohort / observational	Mild dehydration at rest increased fatigue/inertia and impaired concentration.	Mild dehydration & mood/fatigue study (Br J Nutr) (opens in a new tab)
Water / hydration	Do this	Moderate	Cohort / observational	Even ~1-2% dehydration at rest raised fatigue/inertia and impaired concentration; thirst lags, so proactive hydration matters.	Mild dehydration & mood/fatigue study (Br J Nutr) (opens in a new tab)
Belonging (groups / third place)	Watch this	Emerging	Cohort / observational	A sense of belonging buffers the psychosocial stress linked to fatigue.	Loneliness & fatigue longitudinal study (HRS) (opens in a new tab)
Breathing rate	Watch this	Emerging	Mechanistic	Disordered breathing and intermittent hypoxia during sleep flag the sleep-disordered-breathing route to daytime fatigue.	OSA daytime-sleepiness cohort (SESAR) (opens in a new tab)
Colours a day	Watch this	Emerging	Review / narrative	Colourful produce supplies the vitamins and minerals (C, folate, magnesium) that support energy metabolism.	Nutritional status & fatigue review (PMC7071235) (opens in a new tab)
Cook real food	Do this	Emerging	Review / narrative	Home-cooked meals underpin the diet quality tied to lower fatigue.	Nutritional status & fatigue review (PMC7071235) (opens in a new tab)
EPA/DHA (omega-3)	Eat enough of	Emerging	Review / narrative	Omega-3s support skeletal-muscle protein synthesis and mitochondrial function; an emerging, indirect fatigue lever.	Protein/omega-3 & muscle-function review (PMC6116139) (opens in a new tab)
Flexibility (stretching)	Do this	Emerging	RCT / meta-analysis	Mind-body/flexibility work is a minor contributor within the broader activity effect on fatigue.	Physical activity & fatigue meta-analysis (PMC10477297) (opens in a new tab)
Inner circle (close ties)	Watch this	Emerging	Cohort / observational	Close supportive ties protect against the loneliness that predicts fatigue.	Loneliness & fatigue longitudinal study (HRS) (opens in a new tab)
Iodine	Eat enough of	Emerging	Review / narrative	Iodine deficiency lowers thyroid hormone output, a classic cause of tiredness and low energy (cross-links to Thyroid).	Nutrition & thyroid review (PMC11314468) (opens in a new tab)
Niacin (B3)	Eat enough of	Emerging	Review / narrative	Niacin (NAD/NADP) is essential to cellular energy metabolism.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Pantothenic acid (B5)	Eat enough of	Emerging	Review / narrative	B5 (coenzyme A) is required for energy-yielding metabolism.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Riboflavin (B2)	Eat enough of	Emerging	Review / narrative	Riboflavin is a cofactor in mitochondrial energy production; low status contributes to fatigue.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Screens before bed — cut back	Do this	Emerging	Established clinical	Evening screen light delays sleep onset, trimming sleep and worsening next-day fatigue.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Selenium	Eat enough of	Emerging	Review / narrative	Selenium supports thyroid hormone activation (T4->T3); low status can contribute to fatigue via thyroid function.	Nutrition & thyroid review (PMC11314468) (opens in a new tab)
Sleep hygiene - Bedroom	Do this	Emerging	Established clinical	A cool, dark, quiet bedroom supports uninterrupted sleep and morning refreshment.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Sleep hygiene - Clock & light	Do this	Emerging	Cohort / observational	Consistent light/dark timing anchors the circadian clock and next-day alertness.	Morning light & sleep/alertness field study (PubMed 36058557) (opens in a new tab)
Sleep hygiene - Intake & timing	Do this	Emerging	Established clinical	Late heavy meals, alcohol and fluids near bedtime fragment sleep and worsen next-day energy.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Sleep hygiene - Wind-down	Do this	Emerging	Established clinical	Wind-down routines improve sleep continuity, indirectly reducing daytime fatigue.	Excessive daytime sleepiness review (AFP) (opens in a new tab)
Staying in touch (social reps)	Do this	Emerging	Review / narrative	Social connection and support reduce the emotional exhaustion at the core of burnout.	Burnout review (PMC8834764) (opens in a new tab)
Supplement discipline	Do this	Emerging	Review / narrative	Correcting a genuine micronutrient gap (iron, B12, D, magnesium) reduces fatigue; beyond repletion, supplements add little.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Total Sugars	Don't overdo	Emerging	Cohort / observational	High total-sugar meals drive the glycemic swings behind post-meal fatigue.	Postprandial glucose-dip & alertness study (PREDICT) (opens in a new tab)
Vitamin B6	Eat enough of	Emerging	Review / narrative	B6 supports neurotransmitter and energy metabolism; deficiency is linked to fatigue and low mood.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Warmth & quality of ties	Watch this	Emerging	Cohort / observational	Warm, high-quality relationships lower the chronic-stress burden behind fatigue.	Loneliness & fatigue longitudinal study (HRS) (opens in a new tab)
Zinc	Eat enough of	Emerging	Review / narrative	Zinc participates in energy metabolism and immunity; deficiency can present with fatigue.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)

Held for the whole system

Evidence held for General / Whole-body Energy as a whole — 26 sources.In the order the Map holds them: strongest evidence first. That is a statement about the evidence, not about what matters most.
Nutrient or lever	Direction	Strength	Evidence type	What was found	Source
Cardio / VO2max	Watch this	Strong	Cohort / observational	Low cardiorespiratory fitness carried a risk of all-cause mortality comparable to or exceeding traditional risk factors; benefit rose with fitness without a ceiling.	Mandsager et al., JAMA Network Open 2018 (opens in a new tab)
Cardio / VO2max	Watch this	Strong	RCT / meta-analysis	Low cardiorespiratory fitness carried a risk of all-cause mortality comparable to or exceeding traditional risk factors; benefit rose with fitness without a ceiling.	Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis, JAMA 2009 (opens in a new tab)
Cardio / VO2max	Watch this	Strong	RCT / meta-analysis	CRF is a strong, consistent predictor of morbidity and all-cause mortality across 199 cohort studies.	Lang et al., British Journal of Sports Medicine 2024 (overview of meta-analyses, 20.9M observations) (opens in a new tab)
Daytime alertness	Watch this	Strong	Established clinical	Excessive daytime sleepiness is associated with impaired functioning, accidents and increased mortality.	Epworth Sleepiness Scale efficacy review (opens in a new tab)
Inner circle (close ties)	Watch this	Strong	RCT / meta-analysis	Stronger social relationships were associated with 50% higher odds of survival; the effect was strongest for rich social integration.	Social relationships and mortality risk: a meta-analytic review, PLoS Med 2010 (opens in a new tab)
Inner circle (close ties)	Watch this	Strong	RCT / meta-analysis	Weak social connection raised all-cause mortality, on par with major lifestyle risks.	Social connection and mortality meta-analysis 2024 (opens in a new tab)
Loneliness — reduce	Watch this	Strong	RCT / meta-analysis	Loneliness raised mortality risk ~26%, social isolation ~29%, living alone ~32% - comparable to major risk factors.	Holt-Lunstad et al., Perspect Psychol Sci 2015 (meta-analysis) (opens in a new tab)
Loneliness — reduce	Watch this	Strong	RCT / meta-analysis	Loneliness raised all-cause mortality ~14%, social isolation ~35%, living alone ~21%.	Loneliness/isolation and mortality meta-analysis 2024 (86 studies) (opens in a new tab)
Sleep quality (refreshed)	Watch this	Strong	Established clinical	Poor sleep quality is strongly associated with fatigue, physical complaints and reduced quality of life.	Pittsburgh Sleep Quality Index review (Occupational Medicine 2025) (opens in a new tab)
Balance (one-leg stand)	Watch this	Moderate	Cohort / observational	Failing the 10-second one-legged stance was associated with an 84% higher all-cause mortality risk over the next decade (adjusted).	Araujo et al., BJSM 2022 (opens in a new tab)
Balance (one-leg stand)	Watch this	Moderate	Cohort / observational	Failing the 10-second one-legged stance was associated with an 84% higher all-cause mortality risk over the next decade (adjusted).	Successful 10-second one-legged stance performance predicts survival in middle-aged and older individuals, Br J Sports Med 2022 (opens in a new tab)
Belonging (groups / third place)	Watch this	Moderate	RCT / meta-analysis	Rich social integration (community and group ties) was the strongest social predictor of survival (odds ratio ~1.91).	Social relationships and mortality risk: a meta-analytic review, PLoS Med 2010 (opens in a new tab)
Consistency (the weekly dose)	Do this	Moderate	RCT / meta-analysis	Muscle-strengthening was associated with 10-17% lower all-cause mortality; combined with aerobic activity, benefit is greatest.	Momma et al., BJSM 2022 (meta-analysis) (opens in a new tab)
Consistency (the weekly dose)	Do this	Moderate	Cohort / observational	Meeting both aerobic and muscle-strengthening guidelines was associated with the lowest all-cause mortality.	US national cohort, n=416,420 (dose-response) (opens in a new tab)
Daytime alertness	Watch this	Moderate	Cohort / observational	Abnormal or worsening Epworth sleepiness was associated with higher 5-year all-cause mortality.	Veterans cohort (n=17,967, ESS and mortality) (opens in a new tab)
Grip strength	Watch this	Moderate	Cohort / observational	Higher grip strength was associated with lower all-cause mortality across half a million adults.	Celis-Morales et al., BMJ 2018 (UK Biobank) (opens in a new tab)
Grip strength	Watch this	Moderate	RCT / meta-analysis	Pooled cohorts confirm grip strength as an inverse predictor of all-cause mortality.	Wu et al., JAMDA 2017 (meta-analysis) (opens in a new tab)
Lower-body strength (chair stands / sitting-rising)	Watch this	Moderate	Cohort / observational	Probable sarcopenia (low grip or slow chair-stand) raised all-cause mortality (HR 1.77).	CHARLS 9-year cohort (n=11,233) (opens in a new tab)
Lower-body strength (chair stands / sitting-rising)	Watch this	Moderate	Cohort / observational	The lowest sitting-rising scores carried a 5-6x higher all-cause mortality risk in adults 51-80.	Brito et al., Eur J Prev Cardiol 2014 (sitting-rising test) (opens in a new tab)
Movement (breaking up sitting)	Do this	Moderate	RCT / meta-analysis	Higher sedentary time raised all-cause mortality; ~8% of deaths were linked to sedentary behaviour.	Patterson et al., Eur J Epidemiol 2018 (meta-analysis) (opens in a new tab)
Sleep duration	Watch this	Moderate	RCT / meta-analysis	Both short and long habitual sleep were associated with higher all-cause mortality (a U-shaped relationship).	Cappuccio et al., Sleep 2010 (all-cause mortality meta-analysis) (opens in a new tab)
Staying in touch (social reps)	Do this	Moderate	RCT / meta-analysis	Frequent, maintained social contact is associated with higher survival.	Holt-Lunstad et al., 2010/2015 (meta-analyses) (opens in a new tab)
Body Roundness Index	Watch this	Emerging	Cohort / observational	Both very high and very low BRI were associated with higher all-cause mortality (U-shaped).	BRI and all-cause mortality (JAMA Network Open 2024) (opens in a new tab)
Falling & staying asleep	Watch this	Emerging	Established clinical	Insomnia produces daytime fatigue and functional impairment.	Insomnia-fatigue literature (opens in a new tab)
Resting heart rate	Watch this	Emerging	RCT / meta-analysis	Each 10 bpm higher resting heart rate was associated with ~9-17% higher all-cause mortality.	Aune et al., 2017 / Zhang et al., CMAJ 2016 (opens in a new tab)
Resting heart rate	Watch this	Emerging	RCT / meta-analysis	Each 10 bpm higher resting heart rate was associated with ~9-17% higher all-cause mortality.	Aune et al., "Resting heart rate and the risk of cardiovascular disease, total cancer, and all-cause mortality", Nutr Metab Cardiovasc Dis 2017 (opens in a new tab)