The conversation around human longevity is more relevant than ever, especially as recent studies highlight a consistent rise in average lifespan since the 1800s. This trend, however, primarily focuses on life expectancy at birth, which has improved significantly due to better survival rates in infancy. Yet, the increase in life expectancy for adults, particularly those aged 65 and older, has been relatively modest, with an approximate rise of one year every decade over the past several decades. This discrepancy raises critical questions about the relationship between increasing lifespan and the rate of aging, particularly during a time when significant medical advancements in treating aging have not been realized.

Analyzing the Causes of Increased Life Expectancy

Researchers have delved into mortality statistics to uncover insights into these trends. A study from 15 years ago indicated that reductions in early mortality rates and subsequent declines in mortality for older age groups contribute equally to the overall increase in life expectancy. This improvement can be attributed to various factors, including advancements in public health, reduced exposure to severe infections, and general medical progress. However, whether these two contributing factors stem from the same underlying mechanisms remains an open question. It prompts a deeper inquiry into whether a lower accumulation of damage throughout life allows for longer lifespans.

Aging is often defined through its impact on mortality rates; thus, a decrease in mortality due to intrinsic causes could imply a slower aging process. However, whether we can definitively say that aging has slowed down depends on how we define aging itself. This encompasses mechanisms, capabilities, and cellular biology, leading to a nuanced discussion on whether the increase in life expectancy signifies a true deceleration of aging or merely a postponement of its onset.

Is the Rate of Aging Changing?

Human aging involves an increasing risk of mortality as one ages. While average lifespans have surged over the past century, it remains unclear whether this is due to a genuine slowdown in aging or simply a delay in its onset. This hypothesis has been framed in a testable manner, suggesting that the increase in mortality risk with age may represent a fundamental biological constant. Therefore, an increase in life expectancy could reflect a delay in aging. However, if the rate of aging is indeed changing, it suggests that the underlying processes of aging are becoming more sensitive to environmental, behavioral, and historical conditions.

We focus on the actuarial senescence, which describes the exponential increase in mortality risk with age. This phenomenon is well-explained by the classic Gompertz Law, which measures how quickly risk escalates as aging progresses. Yet, since this slope can be influenced by historical events, it complicates our ability to interpret these changes as pure signals of the aging process. Events such as wars, pandemics, and economic crises can have lasting impacts across generations, distorting mortality patterns.

Research Findings

We analyzed intergenerational variations in the Gompertz slope to determine whether changes in aging rates reflect genuine shifts or merely the effects of historical shocks. By collecting mortality data for individuals aged 80 and older across 12 countries, we found no statistical evidence of long-term trends after accounting for these historical shocks. This suggests that there is no significant change in the mechanisms driving the aging process; rather, the findings align with the remnants of shared historical events. This indicates a lack of evidence for ongoing directional changes in individual aging rates.

This stability does not imply that aging is fixed in every aspect. Over the past century, survival rates have shifted to older ages, and average lifespans have increased significantly. These improvements primarily reflect reductions in baseline and background mortality rates rather than a continuous change in the rate of aging. Demographically, even if the onset of aging has been postponed, the rate itself may remain stable.