Genetic Factors Account for Over Half of Lifespan Variation, New Study Suggests

A new study published in the journal Science proposes that genetic factors account for approximately 50% to 55% of the variation in human lifespan. This estimate is notably higher than previous research, which typically suggested a genetic contribution ranging from 6% to 33%. The researchers attribute this revised understanding to a novel methodology that accounts for "extrinsic mortality," referring to deaths caused by external factors such as accidents or infectious diseases, distinguishing them from "intrinsic mortality" related to biological aging and age-related diseases.

Key Findings

The study posits that earlier assessments of lifespan heritability, which is the proportion of variation in a trait attributable to genetic factors, may have underestimated the true genetic influence by not adequately separating extrinsic causes of death from intrinsic ones. Historically, extrinsic factors were more prevalent causes of death, while in modern developed nations, intrinsic causes dominate.

Researchers concluded that when extrinsic mortality is mathematically accounted for, the estimated genetic contribution to lifespan increases to approximately 50% to 55%. The remaining portion of lifespan variation is attributed to random biological effects and environmental factors, including lifestyle choices, diet, exercise, healthcare access, and social relations. This revised figure aligns with observations in laboratory mice and heritability estimates for other complex human traits like height.

Methodology

The research team, which included Professor Uri Alon and Ben Shenhar from the Weizmann Institute of Science in Israel, and Joris Deelen, a geneticist at Leiden University, developed a mathematical model to differentiate between biological aging, which is genetically influenced, and extrinsic causes of death. This model allowed them to refine heritability estimates even when detailed cause-of-death data was unavailable.

The model was calibrated and applied to lifespan data from thousands of twin pairs in Denmark and Sweden, as well as data from siblings of US centenarians. These datasets encompassed individuals born between 1870 and 1935. By isolating the effects of biological aging, the model consistently indicated a lifespan heritability of approximately 50% to 55% across these diverse cohorts. Analysis of a Swedish dataset further suggested that as extrinsic mortality declined throughout the early 20th century, the perceived genetic contribution to lifespan appeared to increase, supporting the model's approach.

Context and Interpretation

The study clarifies that heritability is not a fixed biological property but a measure contingent on the observed population and environmental circumstances. For instance, the earlier 20-25% figure might accurately reflect populations facing significant external threats, while the 50-55% estimate describes populations where such threats are largely absent.

Researchers emphasize that a higher genetic heritability estimate does not diminish the role of individual agency or environmental factors in determining longevity.

Rather, it reflects a shift in the primary drivers of lifespan variation in populations where extrinsic mortality has largely been mitigated. The analogy of human height was used, where improved nutrition has made genetic differences more prominent in explaining height variation.

Implications and Limitations

The findings encourage renewed efforts to identify specific genetic mechanisms involved in aging and longevity. Understanding these pathways could have significant implications for geriatric medicine and the development of therapeutic interventions aimed at promoting longer, healthier lives, particularly as global populations age.

However, the researchers also noted limitations to their approach. The ideal scenario of directly classified intrinsic or extrinsic causes of death is not yet available in comprehensive datasets. Additionally, the model has primarily been tested on populations of Northern European descent, raising questions about its generalizability to other global populations.

Despite the significant genetic component, researchers reiterate that the remaining 50% of lifespan variation is influenced by lifestyle and environment, and individuals are encouraged to optimize these factors. The study provides insights into how different mortality types influence the understanding of lifespan and illustrates how heritability varies across contexts.