Intrinsic Capacity as the Central Construct of Occupational Health for an Ageing Workforce

A New Paradigm for Healthy Work Longevity

The rapid ageing of the global workforce presents a major challenge to occupational health practice. As retirement ages increase and employees remain economically active for longer, occupational health services must evolve beyond determining whether workers are fit for work at a single point in time. Instead, the emphasis should shift towards preserving the capacities that enable individuals to remain healthy, productive, and safe throughout an extended working life. This paradigm aligns with the World Health Organization's (WHO) concept of Healthy Ageing, which is achieved by maintaining Functional Ability through the preservation of Intrinsic Capacity (IC).

Intrinsic Capacity, introduced in the WHO World Report on Ageing and Health (2015), refers to the composite of an individual's physical and mental capacities. Unlike chronological age or disease status, IC reflects biological ageing and provides a measurable construct that predicts future functional decline, disability, dependency, and mortality. The WHO conceptualises IC across five interconnected domains: locomotion, vitality, cognition, psychological capacity, and sensory function. These domains offer a clinically meaningful framework for identifying early functional decline before overt disease or disability becomes apparent.

Although Intrinsic Capacity has gained increasing attention within geriatric medicine, primary care, and healthy ageing research, it has not been systematically incorporated into occupational health practice. Current occupational health models remain largely centred on determining fitness for work, disease surveillance, and regulatory compliance. The most influential conceptual model, Ilmarinen's Work Ability House, describes work ability as the balance between an individual's resources and occupational demands. While the model recognises health and functional capacity as the foundation of work ability, it does not operationalise Intrinsic Capacity as a measurable construct, nor does it provide clinicians with practical guidance for detecting early age-related functional decline.

Several factors may explain why Intrinsic Capacity has not yet become a central construct within occupational health. First, the concept is relatively new and has primarily been implemented in community and primary care settings through WHO's Integrated Care for Older People (ICOPE) programme. Second, comprehensive frameworks such as the International Classification of Functioning, Disability and Health (ICF) are frequently perceived as complex and difficult to apply in routine occupational health practice. Third, occupational health assessments traditionally adopt a cross-sectional approach, focusing on whether a worker is fit at the time of examination rather than monitoring longitudinal trajectories of biological ageing. Finally, many occupational health practitioners have limited formal training in geriatric assessment, reducing opportunities for early recognition of conditions such as mild cognitive impairment, pre-frailty, and declining executive function.

Integrating Intrinsic Capacity into routine occupational health examinations offers an opportunity to transform practice from a reactive, disease-centred model into a proactive, function-centred approach. Workers aged 45 years and above could undergo periodic Intrinsic Capacity screening as part of their routine Periodic Medical Examination. Initial screening would identify potential impairments across the six WHO ICOPE domains, followed by targeted clinical assessments using validated instruments when abnormalities are detected. Annual reassessment would enable occupational health physicians to monitor longitudinal changes in biological ageing and implement timely interventions before substantial functional decline occurs.

Among the domains of Intrinsic Capacity, cognition and locomotion appear particularly relevant to occupational health. Early reductions in executive function may impair complex decision-making and workplace safety long before dementia is clinically diagnosed. Similarly, declining mobility, balance, and lower limb function increase the risk of occupational injuries, falls, and premature work disability. Importantly, many aspects of Intrinsic Capacity remain modifiable through evidence-based interventions. Occupational optimisation, ergonomic redesign, structured physical activity, nutritional support, sleep optimisation, and targeted rehabilitation may preserve or restore capacity, particularly during the pre-frailty stage when functional decline remains reversible.

To operationalise these principles, we propose the Occupational Intrinsic Capacity Assessment (OICA) as the assessment component of the GOLD Framework. OICA provides a structured clinical pathway for occupational health physicians to evaluate, monitor, and manage Intrinsic Capacity within workplace settings. The proposed pathway consists of five sequential stages: (1) rapid screening of Intrinsic Capacity domains during routine occupational health assessments; (2) verification using validated clinical assessment tools; (3) evaluation of the occupational impact of identified impairments; (4) implementation of targeted occupational and lifestyle interventions; and (5) longitudinal monitoring through repeated annual assessments. This workflow translates the WHO Healthy Ageing framework into routine occupational health practice while maintaining a strong emphasis on prevention, optimisation, and sustained work participation.

Positioning Intrinsic Capacity as the central measurable construct of occupational health represents a significant conceptual evolution. Rather than replacing established models such as the Work Ability House, it complements them by providing a practical clinical mechanism for preserving the biological and functional resources upon which work ability depends. In this context, the GOLD Framework functions as the operational bridge between WHO Healthy Ageing principles and occupational health practice, enabling occupational health physicians to move beyond determining fitness for work towards promoting Healthy Work Longevity.