Season of birth and exceptional longevity Leonid A. Gavrilov, Ph.D. Natalia S. Gavrilova, Ph.D. Center on Aging NORC and The University of Chicago Chicago, USA

Month of birth is a useful proxy characteristic for environmental effects acting during in-utero and early infancy development

Limitations of previous studies Many previous studies of month-of-birth effects on mortality were based on calculating mean age at death from cross- sectional death certificates (no exposure information) Even in the case of longitudinal data, there might be spurious month-of-birth effects on longevity because of population heterogeneity (e.g., different seasonal schedule of births for different socio- economic groups)

Within-Family Study of Season of Birth and Exceptional Longevity Advantage: Allows researchers to eliminate confounding effects of between-family variation

Season-of-birth Study of Exceptional Longevity Cases - 1,574 centenarians born in the U.S. in Lifespan information validated using the Social Security Administration Death Master File. Controls – 10,885 their own siblings and 1,083 spouses Method: Conditional logistic regression

Design of the Study

Distribution of individuals by month of birth in percent: centenarians, their shorter-lived siblings survived to age 30 and U.S. population born in our study window ( ) according to the 1900 U.S. Census (IPUMS data)

Multivariate Analysis: Conditional logistic regression

Siblings Born in September-November Have Higher Chances to Live to 100 Within-family study of 9,724 centenarians born in and their siblings survived to age 50

Season of birth and odds to live to 100 Within-family study of siblings VariableAll siblingsSiblings survived to age 30 Siblings survived to age 50 Siblings survived to age 70 Month of birth: January1.13 (0.387)1.11 (0.472)1.11 (0.463)1.09 (0.537) February1.25 (0.101)1.25 (0.109)1.24 (0.124)1.16 (0.303) MarchReference April1.15 (0.320)1.15 (0.337)1.16 (0.320)1.09 (0.567) May1.20 (0.218)1.17 (0.288)1.19 (0.251)1.15 (0.373) June1.20 (0.229)1.00 (0.254)1.18 (0.284)1.11 (0.486) July1.03 (0.855)1.19 (0.991)1.01 (0.941)1.00 (0.990) August1.25 (0.110)1.24 (0.125)1.27 (0.100)1.21 (0.198) September1.44 (0.006)1.43 (0.009)1.45 (0.007)1.39 (0.022) October1.43 (0.008)1.37 (0.021)1.37 (0.022)1.27 (0.099) November1.51 (0.003)1.48 (0.005)1.47 (0.006)1.41 (0.017) December1.17 (0.266)1.13 (0.380)1.17 (0.283)1.11 (0.486) Female sex3.77 (<0.001)3.82 (<0.001)3.80 (<0.001)3.41 (<0.001) Pseudo R Number of observations 12,13210,3939,7248,123

Spouses Born in October-November Have Higher Chances to Live to 100 Within-family study of 1,800 centenarians born in and their spouses survived to age 50

Life Expectancy and Month of Birth Data source: Social Security Death Master File Published in: Gavrilova, N.S., Gavrilov, L.A. Search for Predictors of Exceptional Human Longevity. In: “Living to 100 and Beyond” Monograph. The Society of Actuaries, Schaumburg, Illinois, USA, 2005, pp

Possible explanations These are several explanations of season-of birth effects on longevity pointing to the effects of early-life events and conditions: seasonal exposure to infections, nutritional deficiencies, environmental temperature and sun exposure. All these factors were shown to play role in later-life health and longevity.

High Initial Damage Load (HIDL) Idea "Adult organisms already have an exceptionally high load of initial damage, which is comparable with the amount of subsequent aging-related deterioration, accumulated during the rest of the entire adult life." Source: Gavrilov, L.A. & Gavrilova, N.S The Biology of Life Span: A Quantitative Approach. Harwood Academic Publisher, New York.

Practical implications from the HIDL hypothesis: "Even a small progress in optimizing the early-developmental processes can potentially result in a remarkable prevention of many diseases in later life, postponement of aging-related morbidity and mortality, and significant extension of healthy lifespan." Source: Gavrilov, L.A. & Gavrilova, N.S The Biology of Life Span: A Quantitative Approach. Harwood Academic Publisher, New York.

Acknowledgments This study was made possible thanks to: generous support from the National Institute on Aging grant #R01AG028620

For More Information and Updates Please Visit Our Scientific and Educational Website on Human Longevity: And Please Post Your Comments at our Scientific Discussion Blog: