Is there an adverse effect of sons on maternal longevity?

Impact of fertility on the longevity of older rural Chinese women: an analysis of a longitudinal survey

Background

This study evaluates the impact of fertility during the childbearing period on the longevity of older rural Chinese women and verifies whether any trade-off exists between women’s longevity and their number of children to provide empirical evidence for improving health intervention policies and formulating active fertility policies in low-fertility countries.

Methods

Based on the data of the deaths of 1623 older adults aged 65 and above during 2014–2018 in the Chinese Longitudinal Healthy Longevity Survey, this study explores the relationship between the number of children born and older rural women’s longevity using the ordinary least squares method. Furthermore, the impact of fertility on the longevity of men and women in rural and urban areas, along with other reproductive behaviours on older rural women’s longevity, were analysed.

Results

There was a significant negative correlation between the number of children born and women’s longevity (β = − 0.555, p < 0.05). Additionally, their longevity exhibited a decreasing trend with having birthed more sons and an increasing trend with more daughters. Age at first and last births had a significant positive relationship with rural women’s longevity; however, the effect of fertility on the longevity of older rural and urban men and older urban women was not significant.

Conclusions

It is confirmed that there is a trade-off between fertility and longevity for rural women in China. Future research should focus on compensating for the decline in female longevity caused by the number of children born and promote the concept of a healthy pregnancy, scientific nurture, and gender equality in fertility.

The Relationship Between Children's Gender Composition and Parents' All-Cause Mortality Among Older Adults in Korea

Using data from the Korean Longitudinal Study of Aging (N = 3,356 participants aged 65 or older) and estimating Cox proportional hazard regression models, this study investigated the association between gender composition of children and parents' mortality risk. This study showed that compared with having both daughters and sons, having exclusively daughters (but not exclusively sons) was associated with higher mortality risk. This association, however, was significant for mothers, but not for fathers. To shed light on source of this association, this study distinguished between mothers with only daughters who receive and do not receive regular financial support from children. Results showed that mothers had elevated mortality risk only if they do not receive regular financial support from their children. Traditional caregiving roles of sons for older parents in Korea may lead to a mortality disadvantage among mothers of daughters vis-à-vis a reduction in financial assistance from children.

Are human natal sex ratio differences across the world adaptive? A test of Fisher's principle

Fisher's principle states that natural selection favours an equal number of male and female births at the population level, unless there are sex differences in rearing costs or sex differences in mortality before the end of the period of parental investment. Sex differences in rearing costs should be more pronounced in low- than in high-resource settings. We, therefore, examined whether human development index and sex differences in child mortality contribute to the natural variation in human sex ratio at birth across the globe. As predicted by Fisher's principle, the proportion of male births increased with both increasing male-biased childhood mortality and level of development of each country. However, these relationships were absent after accounting for spatial autocorrelation in the residuals, which our inference is conditioned on. This work shows how the failure to account for residual spatial autocorrelation can lead to incorrect conclusions regarding support for predictions from sex allocation theory.

Accelerated senescence as a cost of reproduction: Testing associations between oxidative stress and reproductive effort in rural and urban women

OBJECTIVES

Oxidative stress is hypothesized to contribute to age-related somatic deterioration. Both reproductive and ecological context may necessitate tradeoffs that influence this outcome. We examined whether measures of lifetime reproductive effort were related to levels of oxidative stress biomarkers in peri- and post-menopausal women and whether associations were moderated by rural or urban residence.

METHODS

We surveyed 263 healthy women (age 62.1 ± 10.0 SD) from rural (N = 161) and urban Poland (N = 102), collecting sociodemographic data and urine samples to analyze biomarkers of oxidative stress (8-oxo-2'-deoxyguanosine, 8-OHdG) and antioxidative defense (copper-zinc superoxide dismutase, Cu-Zn SOD). Linear regression models, adjusted for residence, were used to test for associations between reproductive effort and 8-OHdG and Cu-Zn SOD.

RESULTS

Univariate models demonstrated significant associations between gravidity and the biomarkers of oxidative stress (8-OHdG: R² = 0.042, P ≤ .001; Cu-Zn SOD: R² = 0.123, P ≤ .001). Multivariate models incorporating potential confounding variables, as well as cross-product interaction terms, indicated that gravidity was associated with 8-OHdG (P < .01, R² _adj = 0.067) and Cu-Zn SOD (P = .01, R² _adj = 0.159). Residence (ie, urban vs rural) did not significantly moderate the associations between the biomarkers and reproductive effort.

CONCLUSIONS

Higher lifetime reproductive effort contributes to increases in oxidative stress and antioxidative defenses. Our results provide evidence of potential mechanisms underlying the physiological tradeoffs influencing senescence for women with high reproductive effort. We illustrate the value of applying an evolutionary perspective to elucidate variation in human health and senescence.

Aging, Life History, and Human Evolution

Aging occurs in all sexually reproducing organisms. That is, physical degradation over time occurs from conception until death. While the life span of a species is often viewed as a benchmark of aging, the pace and intensity of physical degradation over time varies owing to environmental influences, genetics, allocation of energetic investment, and phylogenetic history. Significant variation in aging within mammals, primates, and great apes, including humans, is therefore common across species. The evolution of aging in the hominin lineage is poorly known; however, clues can be derived from the fossil record. Ongoing advances continue to shed light on the interactions between life-history variables such as reproductive effort and aging. This review presents our current understanding of the evolution of aging in humans, drawing on population variation, comparative research, trade-offs, and sex differences, as well as tissue-specific patterns of physical degradation. Implications for contemporary health challenges and the future of human evolutionary anthropology research are also discussed.

Sons accelerate maternal aging in a wild mammal

Aging, or senescence, is a progressive deterioration of physiological function with age. It leads to age-related declines in reproduction (reproductive senescence) and survival (actuarial senescence) in most organisms. However, senescence patterns can be highly variable across species, populations, and individuals, and the reasons for such variations remain poorly understood. Evolutionary theories predict that increases in reproductive effort in early life should be associated with accelerated senescence, but empirical tests have yielded mixed results. Although in sexually size-dimorphic species offspring of the larger sex (typically males) commonly require more parental resources, these sex differences are not currently incorporated into evolutionary theories of aging. Here, we show that female reproductive senescence varies with both the number and sex ratio of offspring weaned during early life, using data from a long-term study of bighorn sheep. For a given number of offspring, females that weaned more sons than daughters when aged between 2 and 7 y experienced faster senescence in offspring survival in old age. By contrast, analyses of actuarial senescence showed no cost of early-life reproduction. Our results unite two important topics in evolutionary biology: life history and sex allocation. Offspring sex ratio may help explain among-individual variation in senescence rates in other species, including humans.

Maternal longevity and offspring sex in wild ungulates

In species with sexual size dimorphism, the offspring of the larger sex usually have greater energy requirements and may lead to greater fitness costs for parents. The effects of offspring sex on maternal longevity, however, have only been tested in humans. Human studies produced mixed results and considerable debate mainly owing to the difficulty of distinguishing the effects of sexual dimorphism from sociocultural factors. To advance this debate, we examined how the relative number of sons influenced maternal longevity in four species of free-living ungulates (Soay sheep Ovis aries; bighorn sheep, Ovis canadensis; red deer, Cervus elaphus; mountain goat, Oreamnos americanus), with high male-biased sexual size dimorphism but without complicating sociocultural variables. We found no evidence for a higher cumulative cost of sons than of daughters on maternal longevity. For a given number of offspring, most females with many sons in all four populations lived longer than females with few sons. The higher cost of sons over daughters on maternal lifespan reported by some human studies may be the exception rather than the rule in long-lived iteroparous species.

Impact of the disability trajectory on the mortality risk of older adults in China

Using data from the Chinese Longitudinal Health Longevity Survey of 2005, 2008 and 2011, the authors compared the difference in the disability trajectory (DT) of survivor, decedent and dropped-out survey respondents and examined gender differences in DT using a group-based trajectory model, gender differences in the impact of DT on mortality risk (MR) among older adults, and mediating effects of resources and health status during late life through survival analysis. This analysis shows that the DTs of the survivors, decedents and dropped-out respondents differ remarkably. The trajectories of the decedents generally begin higher and increase more rapidly. Three types of DT exist for both genders: Type 1, the "independent type"; Type 2, the "low start, rapidly increasing in late life type"; and Type 3, the "high start, rapid development type". Women are more likely to experience a DT of functional impairment. Men who experience the Type 3 trajectory suffer the highest MR, followed by those of the Type 1 and Type 2 trajectories. Women who experience the Type 3 trajectory suffer the highest MR, followed by those of the Type 2 and Type 1 trajectories. In addition, economic status, medical treatment, daily care by the family and chronic diseases mediate the impact of DT on MR for both genders, while the mediating effect of emotional support from children was only observed for women.

Offspring sex and parental health and mortality

Increased mortality has been observed in mothers and fathers with male offspring but little is known regarding specific diseases. In a register linkage we linked women born 1925–1954 having survived to age 50 (n = 661,031) to offspring and fathers (n = 691,124). Three approaches were used: 1) number of total boy and girl offspring, 2) sex of the first and second offspring and 3) proportion of boys to total number of offspring. A sub-cohort (n = 50,736 mothers, n = 44,794 fathers) from survey data was analysed for risk factors. Mothers had increased risk of total and cardiovascular mortality that was consistent across approaches: cardiovascular mortality of 1.07 (95% CI: 1.03–1.11) per boy (approach 2), 1.04 (1.01–1.07) if the first offspring was a boy, and 1.06 (1.01–1.10) if the first two offspring were boys (approach 3). We found that sex of offspring was not associated with total or cardiovascular mortality in fathers. For other diseases or risk factors no robust associations were seen in mothers or fathers. Increased cardiovascular risk in mothers having male offspring suggests a maternal disease specific mechanism. The lack of consistent associations on measured risk factors could suggest other biological pathways than those studied play a role in generating this additional cardiovascular risk.

Payback time? Influence of having children on mortality in old age

BACKGROUND

It is known that parents have lower mortality than childless individuals. Support from adult children to ageing parents may be of importance for parental health and longevity. The aim of this study was to estimate the association between having a child and the risk of death, and to examine whether the association increased at older ages when health starts to deteriorate and the need of support from a family member increases.

METHODS

In this nationwide study, all men and women (born between 1911 and 1925 and residing in Sweden), as well as their children, were identified in population registers and followed over time. Age-specific death risks were calculated for each calendar year for individuals having at least one child and for individuals without children. Adjusted risk differences and risk ratios were estimated.

RESULTS

Men and women having at least one child experienced lower death risks than childless men and women. At 60 years of age, the difference in life expectancy was 2 years for men and 1.5 years for women. The absolute differences in death risks increased with parents' age and were somewhat larger for men than for women. The association persisted when the potential confounding effect of having a partner was taken into account. The gender of the child did not matter for the association between parenthood and mortality.

CONCLUSIONS

Having children is associated with increased longevity, particularly in an absolute sense in old age. That the association increased with parents' age and was somewhat stronger for the non-married may suggest that social support is a possible explanation.

Older Parents Benefit More in Health Outcome From Daughters' Than Sons' Emotional Care in China

OBJECTIVE

To examine whether older parents in China would benefit more from daughters' care than from sons' emotional care.

METHOD

Analysis of the unique data sets of the Chinese Longitudinal Healthy Longevity Survey conducted in 2002, 2005, and 2008-2009 in 22 provinces.

RESULTS

As compared with having son(s), having daughter(s) is significantly more beneficial at older ages in China, with regard to maintaining higher cognitive capacity and reducing mortality risk. Such daughter advantages in providing emotional care to older parents are more profound among the oldest-old aged 80+ as compared with the young-old aged 65 to 79 and surprisingly more profound in rural areas as compared with urban areas, even though son preference is much more common among rural residents.

DISCUSSION

We describe how educational campaigns aimed at informing the public about the benefits of daughter(s) for older parents' health outcome could help promote gender equality and reduce traditional son preference, especially in rural China.

Fertility History, Children's Gender, and Post-Reproductive Survival in a Longevous Population

The question of whether mothers' fertility history influences their post-reproductive survival has been addressed frequently in the scientific literature. Using data from Villagrande Strisaili, Sardinia, where longevity is higher than anywhere else in Europe, we analyzed the relationship between the fertility pattern of mothers who survived past age 50 (n = 539) and their post-reproductive lifespan. We find that, after adjustment for potential confounders (mothers' birth cohort, survival of spouse), the mothers who on average delivered their children later displayed a reduced mortality risk (‒2.9 percent for each additional year), supporting previously reported findings. We also find that a male-skewed offspring ratio was associated with decreased mortality risk of mothers, with longer survival of mothers who delivered their sons above age 35 (p = 0.005), a result not found for daughters. So far, no biological explanation has been suggested for the positive effect of delivering sons later in life. We conjecture that in our dataset stronger nonbiological factors such as gender-specific sociocultural and economic factors may have masked the negative effect reported in other populations, for which a biological explanation was proposed.

The impact of children's sex composition on parents' mortality

BACKGROUND

This study explores the relationship between children's sex composition and parents' mortality in a contemporary western society. It improves on earlier research by using a larger and more representative dataset - constructed from registers and encompassing the entire Norwegian population.

METHODS

The analysis is based on discrete-time hazard models, estimated for the years 1980-2008 for women and men born after 1935.

RESULTS

When operationalising sex composition as the "number of boys", coefficients are insignificant in all specifications. However, when considering the three categories "only boys", "only girls" and "mixed sex", I find a small but significant disadvantage of having only girls, compared to having at least one child of each sex, for mothers of two or more children. Having only daughters is associated with a mortality disadvantage compared to having only sons for mothers of two children, but a mortality advantage among mothers with four children. Among women who gave birth to their first child as teenagers, those who have only sons have relatively high mortality. I also find an excess mortality both for mothers of only girls and mothers of only boys in the period 1980-1989.

CONCLUSION

These results lend some support to the notion that there is a larger benefit of the first son or daughter than the later children of the same sex, and especially in the earliest decade of the study period.

Widowhood, illegitimacy, marital reproduction and female longevity in a rural Spanish population

Using data from parish and civil registers in a rural community in northwest Spain (Los Nogales), family reconstitution provided 1502 complete reproductive histories, of which 584 corresponded to first marriages of women dying after their 50th birthday. A homogeneous sample consisting of women married in the period 1877-1899 (N=311) provided information concerning their reproductive performance, including ages at first and last maternity and number of children born alive and surviving, which was related to the mother's post-menopausal longevity, also considering premarital fertility and her marital status (widow/married). The results obtained indicate that mothers with a lower proportion of children dying before the first birthday and the age of 15 (mainly males) have a greater post-reproductive longevity. Moreover, women with a more protracted end to their reproductive period and greater fertility live for more years beyond their 50th birthday. These results do not prove a causality between maternal longevity and more successful reproduction; instead, they are indicative of a holistic condition of health. A wide spectrum of favorable biological and environmental factors will have positive consequences for a woman's life trajectory, affecting both her reproductive performance and her own likelihood of surviving.

Do sons reduce parental mortality?

BACKGROUND

Although sons are thought to impose greater physiological costs on mothers than daughters, sons may be advantageous for parental survival in some social contexts. The authors examined the relationship between the sex composition of offspring and parental survival in contemporary China and Taiwan. Because of the importance of sons for the provision of support to elderly parents in these populations, the authors hypothesised that sons would have a beneficial effect on parental survival relative to daughters.

METHODS

The authors used data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) and the Taiwan Longitudinal Study of Aging (TLSA). The CLHLS sample consisted of 4132 individuals aged 65 years and over in 2002. The TLSA sample comprised two cohorts: 3409 persons aged 60 years and over in 1989 and 2193 persons aged 50-66 years in 1996. These cohorts were followed up for 3, 18 and 11 years, respectively. The Cox proportional hazards model was used to estimate the relationship between the sex composition of offspring and parental mortality.

RESULTS

Based on seven measures of sex composition, no protective effect of sons was found in either China or Taiwan. For example, in the 1989 Taiwan sample, the hazard ratio (HR) for maternal mortality associated with having an eldest son was 0.979 (95% CI 0.863 to 1.111). In Taiwan, daughters may have been more beneficial than sons in reducing mortality in recent years.

CONCLUSION

The authors offer several explanations for these findings, including possible benefits associated with emotional and interpersonal forms of support provided by daughters and negative impacts of conflicts arising between parents and resident daughters-in-law.