Biological standards of living: age at menarche vs height

Is height related to fertility? An evaluation of women from low- and middle-income countries

OBJECTIVES

To present an empirical description of the association between height and lifetime fertility in women from low- and middle-income countries, allowing for flexible functional relationships.

METHODS

A pooled sample (N = 846 257) of women ages 35-49 in Demographic and Health Surveys (DHS) from 64 countries, with regional samples for Latin America, South Asia, and sub-Saharan Africa. Flexibly-estimated structured additive regression models estimate variations in the height-fertility relationship over the height distribution.

RESULTS

Across samples, height is shown to have nonlinear relationships with number of children ever born and age at first birth. Number of children increases with height until a maximum below average height, after which the number of children decreases. Age at first marriage decreases with height until a minimum below average height, and then increases. Except at the shortest heights, much of the variation in fertility is suggested to reflect socioeconomic differences across heights. At the shortest heights, variation is suggested to reflect later ages at first birth, except for women in sub-Saharan Africa.

CONCLUSION

A nonlinear relationship is indicated between height and fertility. Much of the relationship is suggested to reflect height-variations in socioeconomic status and age at first birth.

Medieval menarche: Changes in pubertal timing before and after the Black Death

OBJECTIVES

Bioarcheological evidence suggests stature increased in males but decreased in females after the Black Death (1348-1350 CE). Because tradeoffs between growth and reproduction can result in earlier ages at menarche and lower limb length, we assess menarcheal age between 1120 and 1540 CE to better understand the health of medieval adolescent females before and after the plague.

MATERIALS AND METHODS

Our sample comprises 74 adolescent females from St. Mary Spital, London (1120-1540 CE) within the age range during which menarche occurs (10-25 years). They were assessed as being pre- or post-menarcheal and divided into three groups: Early Pre-Black Death (n = 13), Late Pre-Black Death (n = 38), and Post-Black Death (n = 23). Changes in the ages of pre- and post-menarcheal females were assessed using Mann-Whitney tests.

RESULTS

The average age of post-menarcheal females increased from the Early- to Late Pre-Black Death periods and declined after the Black Death.

CONCLUSIONS

Short stature can reflect unfavorable growth environments, while younger menarcheal age indicates improved living conditions. The paradoxical pattern of female, but not male, stature reduction after the Black Death might reflect the association of early menarche with lower limb length and signal that adolescent females experienced improved health conditions after the epidemic. Our focus on pre- and post-menarche within a limited age span provides a novel approach for inferring average ages of menarche over time. Pathways to skeletal development and reproductive investment are part of an integrated system, providing a bridge between life history research in bioarchaeology and human biology.

The biological standard of living in Indonesia during the 20th century: Evidence from the age at menarche

This article analyses long-term changes in the mean age at menarche (MAM) as a biological indicator of changes in the standard of living in Indonesia. It finds that MAM was about 15.5 for birth cohorts in the late-19th century, decreasing to 14.5 by the 1930s, at which level it stagnated until the gradual decrease resumed since the early 1960s to around 12.5 in the mid-2000s. The article considers that long-term improvements in nutrition, educational attainment and health care explain these trends. An international comparison of long-term changes finds that MAM in Indonesia was much lower than in Korea and China until respectively 1970 and 1990, but comparable to Japan until 1950 and to Malaysia until 1930. The article presents reasons why these differences are unlikely to be related to dissimilarities in climate and ethnicity, and concludes that they are indicative of relative standards of living.

Having more siblings delays menarche in Indonesia

OBJECTIVES

Tanner (1968, Scientific American, 218(1), 21-27) concluded that having more siblings delayed menarche, but many subsequent studies have reported diverging results. We thus aimed to investigate whether the initial conclusion remains valid by controlling for sibship size and birth order together, analyzing a large number of observations, drawing on a nationally representative sample, adjusting for childhood socioeconomic status, and considering a developing country. We additionally aimed to assess the importance of sibling sex for age at menarche.

METHODS

We analyzed 10 212 ever-married women aged 20+ in the last wave of the Indonesian Family Life Survey. We regressed age at menarche on sibship size, birth spacing, and childhood socioeconomic status. We subsequently divided sibship size into the numbers of brothers and sisters.

RESULTS

Having more siblings was related to later menarche, and the relationship was strengthened when the birth order was controlled for. In addition, those born earlier experienced menarche later. Sibling sex was irrelevant to age at menarche, boosting the importance of sibship size itself.

CONCLUSIONS

Our results support the earlier conclusion that having more siblings delays menarche.

The Null Relation between Father Absence and Earlier Menarche

Researchers have claimed that the absence of a biological father accelerates the daughter's menarche. This claim was assessed by employing a large and nationally representative sample of Indonesian women. We analyzed 11,138 ever-married women aged 15+ in the Indonesian Family Life Survey 2015. We regressed age at menarche on the interaction of father absence (vs. presence) and mother absence (vs. presence) at age 12 with or without childhood covariates. For robustness checks, we performed a power analysis, re-ran the same specification for various subgroups, and varied the independent variable of interest. All results produced a null relation between father absence and age at menarche. The power analysis suggests that a false negative was unlikely. Our review of the literature indicates that the claim of the relation between father absence and earlier menarche was based on weak statistical foundations. Other studies with higher-quality datasets tended to find no relation, and our results replicated this tendency. Therefore, the influence of father absence does not appear to be universal.

The Association between Height and Hypertension in Indonesia

There is growing interest in the influence of early-life conditions on the development of disease. Among diseases in adulthood, hypertension is particularly important for the developing world because considerably more people there are and will be afflicted with the disease than in the developed world and hypertensives there are often unaware of their disease status. We employed height as a proxy for the influence of early-life conditions and estimated the relation between height and hypertension status in Indonesia. We analysed 9,597 men and 10,143 women, aged 25-70. We employed a linear probability model to relate height to hypertension status by sex and age. When we controlled for an array of covariates, a 10cm increase in height was related to an approximately 7% point reduction in the likelihood of being hypertensive for both men and women. This is about a quarter of the prevalence of hypertension in Indonesia. This relation was linear and stronger among older individuals. In addition, the pre- and post-pubertal environments (measured by leg and trunk lengths, respectively) contributed similarly to hypertension. Further evidence suggests that women are more likely to be hypertensive at older ages because they are on average shorter than men.

The trend in the relationship of advanced maternal age to preterm birth and low birthweight

PURPOSE

As women in developed countries tend to delay childbearing, it becomes more important to understand the relationship of advanced maternal age to birth outcomes. We aimed to estimate the trend in the relationship of advanced maternal age to preterm birth and low birthweight.

MATERIALS AND METHODS

We analysed 4,264,417 ethnically homogeneous, singleton firstborns, born in hospitals to married couples in South Korea in 1997-2014. We regressed an indicator for preterm birth or low birthweight on advanced maternal age, the baby's sex, advanced paternal age, and a set of socioeconomic status (SES) variables by year. We then collected the coefficient on advanced maternal age and charted its trend. We repeated the same procedure for 4,153,313 second- and third births.

RESULTS

When we controlled for only the baby's sex, the relationship between advanced maternal age and preterm birth dramatically weakened in the 2000s and slightly more thereafter: being an older mother was related to a 3.5% point increase in preterm birth in the late 1990s, but this figure decreased to less than 2% points by the early 2010s. Controlling for advanced paternal age slightly decreased the relationship and controlling for SES hardly affected the relationship. We obtained almost the same results for low birthweight. Second- and third-borns exhibited a declining, much weaker influence of advanced maternal age on the birth outcomes.

CONCLUSIONS

In relative terms, mothers of advanced age were more likely to deliver preterm and low birthweight babies than younger mothers. In absolute terms, however, the risk was small in the 1990s and much smaller in the early 2010s.

Parents are rapidly getting older in South Korea

While scholars and policymakers have investigated the causes and consequences of low fertility, they have neglected a related issue: advanced parental age. This is an important issue because advanced parental age adversely affects babies in the short and long run. South Korea recently topped the list of low-fertility countries, and so this study examined the trends in parental age in this country. We analysed all births between 1997 and 2014, the census for 2000 and 2010, and aggregate marriage data to report the trends in age at first marriage, interval from marriage to first birth, and parental age at first birth and at all births. At every stage, age increased rapidly for both parents. As a result, of babies born to fathers aged 20-54, 20.2% were born to fathers aged 35-54 in 2000 with the proportion increasing to 38.7% in 2010 - almost double in a single decade. The corresponding figures for mothers increased from 6.7% to 17.2% - more than double. Potential parents and policymakers can use this information to time births more appropriately, thereby reducing risks to babies and mothers.

The fatter are happier in Indonesia

PURPOSE

Although obesity and happiness are known to be negatively related in the developed world, little attention has been paid to this relationship in the developing world. We thus investigated the relationship in Indonesia and attempted to explain the underlying rationale.

METHODS

We considered about 12,000 respondents aged 15+ for each gender obtained from the Indonesian Family Life Survey 2007 by relating a measure of happiness to weight-related measures in ordered probit models.

RESULTS

The relationship between obesity and happiness was positive in Indonesia, and this relationship was robust. Our evidence suggests that the contrasting results for the two worlds result from affordability of obesity. That is, while even low socioeconomic status (SES) individuals in the developed world can afford to be obese, only high SES individuals in the developing world can do.

CONCLUSIONS

Our findings imply that obesity prevention in the developing world requires different measures than those used in the developed world.