Pregnancy is linked to faster epigenetic aging in young women.

A central prediction of evolutionary theory is that energy invested into reproduction comes at the expense of somatic maintenance and repair, accelerating biological aging. Supporting this prediction are findings that high fertility among women predicts shorter lifespan and poorer health later in life. However, biological aging is thought to begin before age-related health declines, limiting the applicability of morbidity and mortality for studying the aging process earlier in life. Here, we examine the relationship between reproductive history and biological aging in a sample of young (20 to 22yo) men and women from the Cebu Longitudinal Health and Nutrition Survey, located in the Philippines (n = 1,735). We quantify biological aging using six measures, collectively known as epigenetic clocks, reflecting various facets of cellular aging, health, and mortality risk. In a subset of women, we test whether longitudinal changes in gravidity between young and early-middle adulthood (25 to 31yo) are associated with changes in epigenetic aging during that time. Cross-sectionally, gravidity was associated with all six measures of accelerated epigenetic aging in women (n = 825). Furthermore, longitudinal increases in gravidity were linked to accelerated epigenetic aging in two epigenetic clocks (n = 331). In contrast, the number of pregnancies a man reported fathering was not associated with epigenetic aging among same-aged cohort men (n = 910). These effects were robust to socioecological, environmental, and immunological factors, consistent with the hypothesis that pregnancy accelerates biological aging and that these effects can be detected in young women in a high-fertility context.

Accelerated biological aging six decades after prenatal famine exposure.

To test the hypothesis that early-life adversity accelerates the pace of biological aging, we analyzed data from the Dutch Hunger Winter Families Study (DHWFS, N = 951). DHWFS is a natural-experiment birth-cohort study of survivors of in-utero exposure to famine conditions caused by the German occupation of the Western Netherlands in Winter 1944 to 1945, matched controls, and their siblings. We conducted DNA methylation analysis of blood samples collected when the survivors were aged 58 to quantify biological aging using the DunedinPACE, GrimAge, and PhenoAge epigenetic clocks. Famine survivors had faster DunedinPACE, as compared with controls. This effect was strongest among women. Results were similar for GrimAge, although effect-sizes were smaller. We observed no differences in PhenoAge between survivors and controls. Famine effects were not accounted for by blood-cell composition and were similar for individuals exposed early and later in gestation. Findings suggest in-utero undernutrition may accelerate biological aging in later life.

Diet, Pace of Biological Aging, and Risk of Dementia in the Framingham Heart Study.

OBJECTIVE: People who eat healthier diets are less likely to develop dementia, but the biological mechanism of this protection is not well understood. We tested the hypothesis that healthy diet protects against dementia because it slows the pace of biological aging. METHODS: We analyzed Framingham Offspring Cohort data. We included participants ≥60 years-old, free of dementia and having dietary, epigenetic, and follow-up data. We assessed healthy diet as long-term adherence to the Mediterranean-Dash Intervention for Neurodegenerative Delay diet (MIND, over 4 visits spanning 1991-2008). We measured the pace of aging from blood DNA methylation data collected in 2005-2008 using the DunedinPACE epigenetic clock. Incident dementia and mortality were defined using study records compiled from 2005 to 2008 visit through 2018. RESULTS: Of n = 1,644 included participants (mean age 69.6, 54% female), n = 140 developed dementia and n = 471 died over 14 years of follow-up. Greater MIND score was associated with slower DunedinPACE and reduced risks for dementia and mortality. Slower DunedinPACE was associated with reduced risks for dementia and mortality. In mediation analysis, slower DunedinPACE accounted for 27% of the diet-dementia association and 57% of the diet-mortality association. INTERPRETATION: Findings suggest that slower pace of aging mediates part of the relationship of healthy diet with reduced dementia risk. Monitoring pace of aging may inform dementia prevention. However, a large fraction of the diet-dementia association remains unexplained and may reflect direct connections between diet and brain aging that do not overlap other organ systems. Investigation of brain-specific mechanisms in well-designed mediation studies is warranted. ANN NEUROL 2024;95:1069-1079.

Genetic analysis of selection bias in a natural experiment: Investigating in-utero famine effects on elevated body mass index in the Dutch Hunger Winter Families Study.

Natural-experiment designs that compare survivors of in-utero famine exposure to unaffected controls suggest that in-utero undernutrition predisposes to development of obesity. However, birth rates drop dramatically during famines. Selection bias could arise if factors that contribute to obesity also protect fertility and/or fetal survival under famine conditions. We investigated this hypothesis using genetic analysis of a famine-exposed birth cohort. We genotyped participants in the Dutch Hunger Winter Families Study (DHWFS, N=950; 45% male), of whom 51% were exposed to the 1944-1945 Dutch Famine during gestation and 49% were their unexposed same-sex siblings or "time controls" born before or after the famine in the same hospitals. We computed body-mass index (BMI) polygenic indices (PGIs) in DHWFS participants and compared BMI PGIs between famine-exposed and control groups. Participants with higher polygenic risk had higher BMIs (Pearson r=0.42, p<0.001). However, differences between BMI PGIs of famine-exposed participants and controls were small and not statistically different from zero across specifications (Cohen's d=0.10, p>0.092). Our findings did not indicate selection bias, supporting the validity of the natural-experiment design within DHWFS. In summary, our study outlines a novel approach to explore the presence of selection bias in famine and other natural experiment studies.

Association between infectious exposures in infancy and epigenetic age acceleration in young adulthood in metropolitan Cebu, Philippines.

OBJECTIVES: The drivers of human life expectancy gains over the past 200 years are not well-established, with a potential role for historical reductions in infectious disease. We investigate whether infectious exposures in infancy predict biological aging using DNA methylation-based markers that forecast patterns of morbidity and mortality later in life. METHODS: N = 1450 participants from the Cebu Longitudinal Health and Nutrition Survey-a prospective birth cohort initiated in 1983-provided complete data for the analyses. Mean chronological age was 20.9 years when venous whole blood samples were drawn for DNA extraction and methylation analysis, with subsequent calculation of three epigenetic age markers: Horvath, GrimAge, and DunedinPACE. Unadjusted and adjusted least squares regression models were evaluated to test the hypothesis that infectious exposures in infancy are associated with epigenetic age. RESULTS: Birth in the dry season, a proxy measure for increased infectious exposure in the first year of life, as well as the number of symptomatic infections in the first year of infancy, predicted lower epigenetic age. Infectious exposures were associated with the distribution of white blood cells in adulthood, which were also associated with measures of epigenetic age. CONCLUSIONS: We document negative associations between measures of infectious exposure in infancy and DNA methylation-based measures of aging. Additional research, across a wider range of epidemiological settings, is needed to clarify the role of infectious disease in shaping immunophenotypes and trajectories of biological aging and human life expectancy.

"Epigenetic clocks": Theory and applications in human biology.

All humans age, but how we age-and how fast-differs considerably from person to person. This deviation between apparent age and chronological age is often referred to as "biological age" (BA) and until recently robust tools for studying BA have been scarce. "Epigenetic clocks" are starting to change this. Epigenetic clocks use predictable changes in the epigenome, usually DNA methylation, to estimate chronological age with unprecedented accuracy. More importantly, deviations between epigenetic age and chronological age predict a broad range of health outcomes and mortality risks better than chronological age alone. Thus, epigenetic clocks appear to capture fundamental molecular processes tied to BA and can serve as powerful tools for studying health, development, and aging across the lifespan. In this article, I review epigenetic clocks, especially as they relate to key theoretical and applied issues in human biology. I first provide an overview of how epigenetic clocks are constructed and what we know about them. I then discuss emerging applications of particular relevance to human biologists-those related to reproduction, life-history, stress, and the environment. I conclude with an overview of the methods necessary for implementing epigenetic clocks, including considerations of study design, sample collection, and technical considerations for processing and interpreting epigenetic clocks. The goal of this review is to highlight some of the ways that epigenetic clocks can inform questions in human biology, and vice versa, and to provide human biologists with the foundational knowledge necessary to successfully incorporate epigenetic clocks into their research.

Germline epigenetic inheritance: Challenges and opportunities for linking human paternal experience with offspring biology and health.

Recently, novel experimental approaches and molecular techniques have demonstrated that a male's experiences can be transmitted through his germline via epigenetic processes. These findings suggest that paternal exposures influence phenotypic variation in unexposed progeny-a proposal that runs counter to canonical ideas about inheritance developed during the 20th century. Nevertheless, support for paternal germline epigenetic inheritance (GEI) in nonhuman mammals continues to grow and the mechanisms underlying this phenomenon are becoming clearer. To what extent do similar processes operate in humans, and if so, what are their implications for understanding human phenotypic variation, health, and evolution? Here, we review evidence for GEI in human and nonhuman mammals and evaluate these findings in relation to historical conceptions of heredity. Drawing on epidemiological data, reproductive biology, and molecular embryology, we outline developments and opportunities for the study of GEI in human populations, emphasizing the challenges that researchers in this area still face.

Evolutionary life history theory as an organising framework for cohort studies: insights from the Cebu Longitudinal Health and Nutrition Survey.

By tracking a group of individuals through time, cohort studies provide fundamental insights into the developmental time course and causes of health and disease. Evolutionary life history theory seeks to explain patterns of growth, development, reproduction and senescence, and inspires a range of hypotheses that are testable using the longitudinal data from cohort studies. Here we review two decades of life history theory-motivated work conducted in collaboration with the Cebu Longitudinal Health and Nutrition Survey (CLHNS), a birth cohort study that enrolled more than 3000 pregnant women in the Philippines in 1983 and has since followed these women, their offspring and grandoffspring. This work has provided evidence that reproduction carries "costs" to cellular maintenance functions, potentially speeding senescence, and revealed an unusual form of genetic plasticity in which the length of telomeres inherited across generations is influenced by reproductive timing in paternal ancestors. Men in Cebu experience hormonal and behavioural changes in conjunction with changes in relationship and fatherhood status that are consistent with predictions based upon other species that practice bi-parental care. The theoretical expectation that early life cues of mortality or environmental unpredictability will motivate a "fast" life history strategy are confirmed for behavioural components of reproductive decision making, but not for maturational tempo, while our work points to a broader capacity for early life developmental calibration of systems like immunity, reproductive biology and metabolism. Our CLHNS findings illustrate the power of life history theory as an integrative, lifecourse framework to guide longitudinal studies of human populations.

Genome-wide analysis of DNA methylation in relation to socioeconomic status during development and early adulthood.

OBJECTIVES: Socioeconomic status (SES) is a powerful determinant of health, but the underlying biological mechanisms are poorly understood. This study investigates whether levels of DNA methylation at CpG sites across the genome are associated with SES in a cohort of young adults in the Philippines. METHODS: DNA methylation was assayed with the Illumina HumanMethylation450 Bead Chip, in leukocytes from 489 participants in the Cebu Longitudinal Health and Nutrition Survey (mean age = 20.9 years). SES was measured in infancy/childhood and adulthood, and was based on composite measures of income, assets, and education. Genome-wide analysis of variable probes identified CpG sites significantly associated with SES after adjustment for multiple comparisons. Functional enrichment analysis was used to identify biological pathways associated with these sites. RESULTS: A total of 2,546 CpG sites, across 1,537 annotated genes, were differentially methylated in association with SES. In comparison with high SES, low SES was associated with increased methylation at 1,777 sites, and decreased methylation at 769 sites. Functional enrichment analysis identified over-representation of biological pathways related to immune function, skeletal development, and development of the nervous system. CONCLUSIONS: Socioeconomic status predicts DNA methylation at a large number of CpG sites across the genome. The scope of these associations is commensurate with the wide range of biological systems and health outcomes that are shaped by SES, and these findings suggest that DNA methylation may play an important role.