Interaction Between Fertility and Longevity in a Long-Living Population : Villagrande (1830 – 2012)
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Interaction between fertility and longevity in a long-living population : Villagrande (1830 – 2012) Michel POULAIN1,2, Anne HERM1,2, Dany CHAMBRE and Gianni PES3 1 Estonian Institute for Population Studies, Tallinn University, Estonia 2 IACCHOS, Université catholique de Louvain, Louvain-la-Neuve, Belgium. 3 Department of Biomedical Sciences – Università degli Studi di Sassari - Italy Please do not quote this contribution and use its results before publication 1. Question addressed The interactions between fertility and duration of life are multiple and complex and have been discussed long but findings are not fully consistent. Based on historical genealogical data over 200 years Freeman (1935) found no evidence of association between number of children and the length of post-reproduction life of mother while there was slight association between age at marriage and duration of life. By reviewing the results of a large number of studies on post-reproductive longevity Helle et al. (2005) showed that over more than 30 investigated studies, the most reported positive relationship exists between late reproduction and longevity of mothers. At opposite, the age at first childbirth has in most studies no significant relation to survival of mothers above age 50 as well as the total number of children. Nevertheless, in a historical French-Canadian cohort of the 17th-18th century experiencing natural fertility, Müller et al (2002) found that higher number of children was linked with increased post-reproduction survival while Westendorp et al. (1998) have shown the opposite with British aristocratic families. Dobblhammer et al. (2000) demonstrated that mothers with larger number of children have lower relative mortality risks in contemporary populations in England and Austria. Individual data are largely preferable for analyzing the association between reproductive behaviour and longevity but very often the small size of the populations involved introduces limitations for the statistical signification of the findings. Individual data used often represent historical pre-transition populations (Helle et al, 2005, Smith et al. 2009, Muller, 2002). A recent study by Dribe (2012) on Swedish historical population (1790-1880) demonstrated a positive effect of number of children ever born on mortality of mothers, but not of fathers. He showed also that the mortality risk is higher for women who had their last child relatively earlier. Some studies used representative longitudinal data or combined aggregated data with individual data on vital events for more recent (post- transition) populations (Hank et al. 2010, Tabatabaie et al., 2011, Astolfi et al 2007). Compared to studies on pre-transition populations their findings showed that links between late maternity and the chances for survival in older age of mothers seem to be less obvious. Few researches consider the relation between the reproductive history and exceptional longevity. According Tabatabaie et al., (2011) centenarians in Ashkenazi Jewish community have had both their first and last childbirths at later age and had fewer children than individuals who did not survive up to such an old age. Caselli et al. (2012) found by analysing Sardinian centenarians that women who reach 100 years seems to have on average fewer children, and apparently at an older age, particularly for their last children Some historical data involve the follow-up of population during a large period that covers the pre-transitional, transitional and post-transitional periods. Such data allows analyzing the interaction between fertility and mortality during the fertility transition and more specifically to investigate the relation between the decline of infant mortality and the decrease of fertility (Van Poppel 2012). Among all possible interactions between fertility and longevity we choose the following question that is of particular interest for the Sardinian population: Question addressed. How the reproductive history of mothers is associated with their survival above 50 years of age? More specifically we would like to test at individual level if a later age at last child is associated with better survival for mothers, an association found at aggregated level of municipalities in Sardinia by Astolphi et al. (2007, 2009). The aim of this contribution is to address this question in a population characterised by exceptional longevity. 2. The context and the choice of the population investigated The data collected on the population and families of the Sardinian village of Villagrande Strisaili is among the most suitable for study of possible interaction between fertility and longevity for several reasons. 1. Sardinian late fertility transition and high level of marital fertility has been reported by numerous researchers (Livi Bacci 1977, Bernardi 2007). Still in 1950’s the province of Nuoro in the mountainous part of Sardinia showed the highest values for the Coale Index on marital fertility Ig among all Italian provinces during the fertility transition (figure 1). 2. Sardinia as whole but more specifically some in-land regions of the island, mostly in the Nuoro province, were still recently characterised also by late maternity (Astolfi et al. 2007, 2009). 3. Sardinia and more specifically the Nuoro province are also experiencing an extreme situation as far as the proportion of oldest olds and longevity are concerned. At the 1981 census, the Nuoro province presented the highest proportion of oldest olds (P85+/P60+), (Cantalini et al. 1990) but also the higher male life expectancy (Salaris 2008). An area named Longevity Blue Zone and composed by 14 municipalities located in the Ogliastra and the Nuoro provinces has been characterised by an exceptionally high male longevity (Poulain et al. 2004). 4. The idea of a possible relation between late maternity and higher longevity has been launched in Sardinia by Astolfi et al. (2007). Based on aggregated data on Sardinian municipalities, they demonstrated that areas with persistent late maternity are also characterized by longer life span, suggesting that the extension of both reproductive and post-reproductive period might be influenced by common determinants. Considering ‘late maternity’ through the proportion of babies born to mothers aged 35 years and older, they identified different spatial pattern in Sardinia where late maternity accompanies relatively low neonatal mortality. Also Tentoni et al (2011) suggested that the late maternity could be associated with a longer life span and correlated with the genetic structure of the local population. The similarity of the spatial patterns on maternal reproductive traits and longevity suggests this association at aggregated level. Sardinia was said to be a candidate for studies on the association of the life longevity with reproductive longevity (Astolfi et al. 2009) and the Longevity Blue Zone in the Nuoro province represent the most interesting place for a more in-depth analysis of the relation between late fertility and longevity. 5. More recently Caselli et al (2012) have investigated the relation between reproductive behaviour and extreme longevity based on data on Sardinian centenarians and various control groups. The preliminary results demonstrate that women who live longer seems to have on average fewer children, and apparently at an older age, particularly for their last children. More concretely they found that having a child at 40 years or older has a protective effect on mother’s survival, while the total number of children as well as the age at first childbirth seem to have no significant effect. 6. Pozzi (2008) analysed data at individual level using civil records of birth and death for the population of Alghero, a city on the sea-side, for the period 1866-1920, and two villages located in the Longevity Blue Zone, Talana and Urzulei, from 1866 till 1935. The lowest infant mortality in Sardinia already identified by Coletti (1908) and Gatti (2002) was confirmed and the situation was more pronounced in Urzulei compared to Alghero (Table 1). At the opposite, the child mortality from 2 to 5 is found higher in Sardinia (Gatti 2002, Salaris 2008). Pozzi expressed that unfortunately the period covering years following WWI are not explored at micro level. Finally, for the setting for our investigation, the village of Villagrande Strisailli was chosen as the village of the Longevity Blue Zone showing the highest extreme longevity index, e.g. the larger proportion of newborns reaching age 100 in the whole Sardinia (Poulain et al. 2004). 3. Setting, data and methods The village of Villagrande is located at 700 meters above sea level in the province of Ogliastra, but the altitude of its territory ranges from sea level to Punta La Marmora at 1,834 meters. On 1 January 2010, 3,441 inhabitants lived in Villagrande (ISTAT) with agro- pastoral activities and traditional life style still prevalent. Despite the fact that until the 1960s this region was among the poorest within the island, recent economic developments brought the population of this area close to the average welfare standard of the Italian population. Demographic genealogical data on the whole population of the village has been collected. The start and end points of the database as marked by earliest birth included and last deaths ranges from year 1826 up to 2012. The families have been reconstructed for couples that registered their civil marriage in Villagrande starting 1851 up to 1955. Data are based on parish records up to 1865 and on civil records starting from 1866. The civil records were satisfactory crosschecked by information from parish records for the first decade of civil registration to ensure he exhaustive coverage of newborns. A total of 1067 family nucleus composed by a couple having at least one child were reconstructed including 5788 children. 1029 different women are involved in the 1067 families, meaning that 38 women married twice and had children from more than one husband. Among these women, we identified 702 women that are mothers in completed families in a sense that both spouses marry only once and both survived up to the end of the fertility period of the mother.