The General Guideline: Age 65+
According to the official NIH Style Guide, the National Institute on Aging (NIA) generally describes older adults as individuals aged 65 or older. However, the guide emphasizes that this is a general description and that the definition can vary significantly. The guidance also strongly recommends using the term “older adults” instead of outdated terms like “the elderly” or “senior citizens,” as it affirms agency and personhood.
This standard of age 65 is largely based on historical precedent rather than a biological milestone. For example, age 65 was chosen as the retirement age in Germany and later became the eligibility age for Medicare in the United States. While this chronological age is a useful benchmark for legal and financial purposes, the NIH recognizes its limitations in reflecting the vast biological and functional diversity of the aging population.
The Nuance in NIH Research and Policy
For the purpose of human subjects research, the NIH operates under a more detailed policy called "Inclusion Across the Lifespan." This policy mandates that individuals of all ages, including older adults, must be included in all human subjects research unless there is a specific, scientifically or ethically based reason to exclude them. A study proposing to exclude older adults must provide a robust justification, such as when:
- The disease or condition being studied does not affect the excluded age group.
- Existing knowledge on the research topic is already sufficient for the excluded age group.
- A separate, age-specific study is more appropriate.
This policy highlights a shift away from arbitrary, one-size-fits-all age limits in research, which historically led to the exclusion of older adults from clinical trials. By promoting broader inclusion, the NIH aims to ensure that research findings are applicable to the entire population that a given disease or condition affects, ultimately improving outcomes for older individuals.
The Limitation of Chronological Age
One of the central tenets of modern gerontology is that chronological age is a poor predictor of health and function. The NIH acknowledges that the aging process is not uniform across individuals due to differences in genetics, lifestyle, and overall health. A person's chronological age (their age in years) can differ significantly from their biological and psychological age.
- Biological age refers to the physiological changes that occur with aging. Some individuals may be biologically older or younger than their chronological age due to genetics or lifestyle factors.
- Psychological age is based on how people feel and act. An individual who remains active, engaged, and forward-looking is considered psychologically younger than one who is not.
This heterogeneity is why a single definition based on chronological age is insufficient for clinical and research applications. The National Institute on Aging, therefore, encourages researchers to justify age ranges based on the specific scientific question rather than imposing a blanket cutoff.
Comparison: Chronological Age vs. Functional Age
| Aspect | Chronological Age | Functional Age |
|---|---|---|
| Basis | Passage of time (years, months) | Health, genetics, lifestyle, and function |
| Predictive Value | Predicts legal/financial milestones (e.g., Medicare eligibility) | Better predicts health outcomes and individual needs |
| Uniformity | Universal and standardized | Varies significantly between individuals |
| Clinical Relevance | Limited on its own, but used as a general marker | Crucial for personalized care, treatment plans, and research inclusion |
| Research Use | Used as a benchmark; NIH avoids arbitrary exclusions | Used to design representative studies that reflect patient heterogeneity |
Sub-classifications of Older Adulthood
To better address the wide-ranging needs and characteristics of the aging population, gerontologists and researchers often subdivide the 65+ group into more specific categories. This practice allows for a more accurate portrayal of life changes and health challenges associated with different stages of later life. Common sub-classifications include:
- Young-old: Ages 65–74
- Middle-old: Ages 75–84
- Oldest-old: Ages 85 and older
Research has shown significant differences between these groups. For instance, the oldest-old may face greater physical and social challenges and are more likely to have longer hospital stays and higher rates of admission. Using these sub-classifications in research helps to produce more precise and relevant findings for specific segments of the older adult population.
Ensuring Inclusive and Relevant Research
As outlined in its "Inclusion Across the Lifespan" policy, the NIH and its institutes, like the National Institute on Aging, work to ensure research benefits all age groups. Prior to the policy's implementation, older adults were often arbitrarily excluded from research, leading to a significant knowledge gap. Today, researchers must consider how their study design and protocols can accommodate the needs of older participants, such as mobility issues, cognitive impairments, or comorbidities. This focus on inclusivity reflects a commitment to creating research that is both scientifically rigorous and ethically sound. For additional information on federal research initiatives involving older adults, the NIA is a key resource. Visit their website at nia.nih.gov to learn more about the institute's goals and projects.
Conclusion
While the National Institutes of Health and its component, the National Institute on Aging, generally use age 65 as a benchmark for older adults, this simple chronological definition is just the starting point. For clinical research and policy, the NIH embraces a more comprehensive, nuanced approach. This includes a policy of inclusivity that moves beyond arbitrary age cutoffs and recognizes the vast heterogeneity of the aging population. By considering factors like biological and psychological age and sub-classifying older adults, the NIH ensures that research is both representative and ultimately more effective in improving the health and well-being of all older individuals.
