Anaemia, Fatigue, and Physical Function in Later Life

Key Takeaways

Anaemia is a reduction in circulating haemoglobin below a defined threshold; it becomes more common with advancing age but is not considered an inevitable or harmless feature of ageing. [1] [2]
Lower haemoglobin can reduce blood oxygen-carrying capacity, providing a plausible route from anaemia to exertional fatigue and lower physical capacity. [3] [4]
In observational studies of older adults, anaemia is associated with weaker muscle strength, slower or poorer physical performance, disability, and subsequent functional decline. [5] [6] [7]
These associations are not proof that anaemia alone causes functional loss, because inflammation, kidney disease, nutritional deficiency, bleeding, malignancy, and other chronic conditions can influence both haemoglobin and function. [1] [8] [9]

Anaemia sits at the intersection of haematology and healthspan. Haemoglobin within red blood cells carries oxygen, while walking, rising from a chair, maintaining balance, and other everyday tasks require adequate oxygen delivery as well as intact cardiovascular, respiratory, neurological, and muscular systems. Anaemia can therefore contribute to fatigue and reduced capacity, but the same functional findings may also reflect the disease process that produced the anaemia. [1] [3] [4]

Who This Is Useful For

This page is useful for readers interpreting haemoglobin, fatigue, walking speed, grip strength, disability, or frailty findings in studies of older populations. It is especially relevant when an observational study reports that anaemia predicts poorer function but cannot fully separate the effect of low haemoglobin from comorbidity and the cause of the anaemia. [5] [7] [10]

What Anaemia Measures

Anaemia is usually classified from blood haemoglobin concentration rather than from fatigue or physical performance. Widely used population criteria apply different haemoglobin thresholds to men and women, but reviews note that threshold choice, age, population, laboratory context, altitude, and underlying disease affect prevalence estimates and interpretation. A binary label can also hide variation within both the anaemic and non-anaemic ranges. [1] [2] [5]

Fatigue is not part of the laboratory definition. Some people with mild anaemia report little fatigue, whereas fatigue can be substantial without anaemia. Haemoglobin and fatigue should therefore be treated as related but distinct measures: one is a blood measurement, and the other is a subjective experience shaped by activity, symptoms, mood, sleep, disease burden, and physiological reserve. [1] [11]

Why Anaemia Has Multiple Causes in Later Life

Anaemia in older adults is heterogeneous. Reviews describe iron deficiency and blood loss, vitamin B12 or folate deficiency, chronic inflammation, chronic kidney disease, malignancy, bone-marrow disorders, and medication-related or other causes. More than one process may be present in the same person. [1] [8] [9]

Inflammation can increase hepcidin signalling, restrict the availability of iron for red-cell production, suppress erythropoiesis, and shorten red-cell survival. Reduced kidney function can impair the erythropoietin response that normally stimulates red-cell production. These pathways can overlap with nutritional deficiency or occult blood loss, making a single-cause account unreliable. [8] [9]

A residual category is often called unexplained anaemia of ageing after recognized causes have not been identified. Studies have reported an inappropriately low erythropoietin response in some of these cases, while contemporary reviews also discuss clonal haematopoiesis and other age-related changes. The term describes the limits of current classification rather than one established mechanism. [1] [8] [12]

From Haemoglobin to Fatigue and Function

Level	Observed or Proposed Link	Interpretive Limit
Blood	Less haemoglobin reduces oxygen-carrying capacity. [3] [4]	Haemoglobin concentration does not by itself measure tissue oxygen use or symptoms. [1] [3]
Exertion	Lower oxygen delivery may increase the relative effort of walking or other activity and contribute to fatigue. [3] [11]	Fatigue is nonspecific and can arise through many non-haematological pathways. [1] [11]
Performance	Anaemia is associated with lower grip strength and poorer lower-extremity performance in older cohorts. [5] [11]	Most evidence is observational and vulnerable to residual confounding. [5] [11]
Daily function	Anaemia has been associated with disability and later decline in activities of daily living. [6] [7]	Comorbidity can explain part of the association, and results vary by outcome and cohort. [7] [10]

Oxygen Delivery Is a Plausible, Incomplete Mechanism

Oxygen delivery depends on haemoglobin concentration, arterial oxygen saturation, cardiac output, and regional blood flow. Total haemoglobin and red-cell mass are important determinants of maximal exercise capacity, so reduced haemoglobin offers a biologically plausible explanation for exertional limitation. Compensatory increases in heart rate and blood flow may preserve oxygen delivery at rest more readily than during demanding activity. [3] [4]

This mechanism is incomplete because everyday function is not a maximal exercise test. Muscle mass and quality, balance, pain, cognition, motivation, cardiopulmonary reserve, and habitual activity all affect performance. The severity and speed of onset of anaemia also influence whether symptoms appear. [1] [4] [5]

Evidence from Physical-Function Studies

In the cross-sectional InCHIANTI study, older adults with anaemia had more disability, poorer lower-body performance, and lower muscle strength than participants without anaemia after statistical adjustment for several health characteristics. Because exposure and outcome were measured together, the study could establish association but not direction of cause. [5]

Longitudinal cohort evidence strengthens the temporal link without resolving causality. In older community-dwelling adults, baseline anaemia was associated with greater decline over four years in a performance score combining walking speed, standing balance, and chair rises. In the Leiden 85-plus Study, baseline and incident anaemia were associated with decline in selected activity-of-daily-living domains, although adjustment for comorbidity changed some cross-sectional findings. [6] [7]

Studies in very old adults and mixed geriatric outpatient samples also report associations between lower haemoglobin, weaker grip, greater fatigue, disability, and poorer self-reported physical health. Their different populations and measures support broad consistency, but they do not make the estimated effect interchangeable across settings. [10] [11]

Anaemia, Frailty, and Shared Causes

Anaemia and frailty overlap but are not synonyms. A systematic review and meta-analysis of observational studies found higher odds of frailty among people with anaemia, with substantial heterogeneity and only limited longitudinal evidence. Exhaustion, weakness, slow walking, and low activity can connect the two constructs at the level of measured phenotype. [13]

Shared causes are equally important. Inflammation, kidney disease, malnutrition, cancer, and multimorbidity can contribute both to anaemia and to loss of physiological reserve. Statistical adjustment can reduce measured confounding but cannot ensure that every relevant pathway has been captured, particularly when disease severity and activity are measured imperfectly. [1] [7] [9] [13]

Evidence Quality and Interpretation

Confidence is strong that anaemia in later life is heterogeneous and that lower haemoglobin is associated with fatigue, poorer physical performance, and disability across multiple observational cohorts. A reduced capacity to carry oxygen supplies a coherent physiological link, while longitudinal studies show that anaemia can precede measured functional decline. [1] [3] [6] [7]

Confidence is weaker about how much of any individual's decline is caused directly by anaemia, which haemoglobin threshold best captures functional risk, and whether changing haemoglobin alone reverses disability across causes and populations. Observational associations, threshold variation, selection of healthier or sicker cohorts, and residual confounding limit causal interpretation. [1] [5] [7] [13]

What This Does Not Mean

It does not mean fatigue establishes that anaemia is present; fatigue is a nonspecific symptom and anaemia is defined by a blood measurement. [1] [11]
It does not mean anaemia is a normal consequence of chronological ageing; recognized diseases and deficiencies account for many cases, while an unexplained category remains after evaluation. [1] [2] [12]
It does not mean low haemoglobin is always the sole cause of weakness or mobility loss; shared disease pathways and functional determinants can confound the relationship. [5] [7] [9]
It does not mean every association demonstrates that raising haemoglobin would restore function; causal effects depend on aetiology, population, severity, and the outcome being measured. [1] [13]

Practical Interpretation Examples

If an anaemic group walks more slowly: the result is compatible with reduced oxygen-carrying capacity, but differences in disease burden, muscle strength, pain, and activity must also be considered. [3] [5]
If haemoglobin predicts later disability: the temporal sequence is more informative than a cross-sectional correlation, yet it still does not eliminate shared causes or residual confounding. [6] [7]
If fatigue improves while haemoglobin is unchanged: this is not contradictory, because fatigue also reflects sleep, mood, symptoms, activity context, and other physiological systems. [11]

Summary

Anaemia is a laboratory-defined state with several possible causes, while fatigue and physical function describe how a person feels and performs. Reduced oxygen-carrying capacity creates a plausible bridge between them, and observational evidence consistently links anaemia with weaker performance and greater disability in later life. The relationship remains multidirectional: anaemia may contribute to decline, and the conditions that cause anaemia may independently reduce healthspan. [1] [5] [6] [9]

References

Stauder, R., Valent, P., & Theurl, I. (2018). Anemia at older age: etiologies, clinical implications, and management. Blood. https://pubmed.ncbi.nlm.nih.gov/29141943/
Guralnik, J. M., Eisenstaedt, R. S., Ferrucci, L., Klein, H. G., & Woodman, R. C. (2004). Prevalence of anemia in persons 65 years and older in the United States: evidence for a high rate of unexplained anemia. Blood. https://pubmed.ncbi.nlm.nih.gov/15238427/
Poole, D. C., & Jones, A. M. (2012). Oxygen uptake kinetics. Comprehensive Physiology. https://pubmed.ncbi.nlm.nih.gov/23798293/
Hureau, T. J., Weavil, J. C., Thurston, T. S., et al. (2021). The oxygen cascade during exercise in health and disease. Molecular Aspects of Medicine. https://pmc.ncbi.nlm.nih.gov/articles/PMC8026750/
Penninx, B. W. J. H., Pahor, M., Cesari, M., et al. (2004). Anemia is associated with disability and decreased physical performance and muscle strength in the elderly. Journal of the American Geriatrics Society. https://pubmed.ncbi.nlm.nih.gov/15086651/
Penninx, B. W. J. H., Guralnik, J. M., Onder, G., et al. (2003). Anemia and decline in physical performance among older persons. The American Journal of Medicine. https://pubmed.ncbi.nlm.nih.gov/12893396/
den Elzen, W. P. J., Willems, J. M., Westendorp, R. G. J., et al. (2009). Effect of anemia and comorbidity on functional status and mortality in old age: results from the Leiden 85-plus Study. Canadian Medical Association Journal. https://pmc.ncbi.nlm.nih.gov/articles/PMC2717683/
Ferrucci, L., Guralnik, J. M., Bandinelli, S., et al. (2007). Unexplained anaemia in older persons is characterised by low erythropoietin and low levels of pro-inflammatory markers. British Journal of Haematology. https://pmc.ncbi.nlm.nih.gov/articles/PMC2669300/
Picca, A., Coelho-Junior, H. J., Calvani, R., et al. (2024). Anemia and its connections to inflammation in older adults: a review. Journal of Clinical Medicine. https://pmc.ncbi.nlm.nih.gov/articles/PMC11012269/
Giovannini, S., Onder, G., Liperoti, R., et al. (2018). Hemoglobin concentration is associated with self-reported disability and reduced physical performance in a community dwelling population of nonagenarians: the Mugello Study. BMC Geriatrics. https://pmc.ncbi.nlm.nih.gov/articles/PMC5691100/
Thein, M., Ershler, W. B., Artz, A. S., et al. (2009). Diminished quality of life and physical function in community-dwelling elderly with anemia. Medicine. https://pmc.ncbi.nlm.nih.gov/articles/PMC2893336/
Guralnik, J., Ershler, W. B., Artz, A. S., et al. (2022). Unexplained anemia of aging: etiology, health consequences, and diagnostic criteria. Journal of the American Geriatrics Society. https://pubmed.ncbi.nlm.nih.gov/34796957/
Palmer, K., Vetrano, D. L., Marengoni, A., et al. (2018). The relationship between anaemia and frailty: a systematic review and meta-analysis of observational studies. Journal of Nutrition, Health & Aging. https://pubmed.ncbi.nlm.nih.gov/30080223/

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