Is there an adverse effect of sons on maternal longevity?

Abstract

Recent years have witnessed the emergence of a literature examining the effects of giving birth to sons on postmenopausal longevity in pre-industrial mothers. The original paper in this lineage used a sample (nZ375) of Sami mothers from northern Finland and found that, relative to daughters, giving birth to sons substantially reduced maternal longevity. We examine this hypothesis using a similar and a much larger sample (nZ930) of pre-industrial Sami women from northern Sweden, who in terms of their demographic, sociocultural and biological conditions, closely resemble the original study population. In contrast to the previously reported results for the Sami, we find no evidence of a negative effect of sons on maternal longevity. Thus, we provide the most compelling evidence to date that the leading result in the literature must be approached with scepticism.

On the number of sons born and shorter lifespan in historical Sami mothers

“…This finding supports the hypothesis that energetic resources invested in reproduction by the mothers may compromise those resources available for longevity (Kirkwood & Rose 1991). Using similar but a larger dataset of Sami mothers from Sweden, a neighbouring country of Finland, Cesarini et al (2009) found no evidence for the association between sons born and the mothers' post-menopausal lifespan. The authors made two main conclusions: (i) our results were likely to be false-positive because of smaller sample size and (ii) that current evidence for the association between offspring sex and maternal longevity is rare and restricted to these Finnish Sami only.…”

“…Based on their larger sample size and non-significant results, Cesarini et al (2009) seem to suggest that our findings were false-positive. Our original publication was based on all Sami women resident in three Finnish Sami populations between 1640 and 1870, but we were unable to include all these women in our analysis because of missing records on their age at death.…”

“…One of the main points emphasized in our original contribution but untested by Cesarini et al (2009) was that children may not have an adverse association on their mother's lifespan only, but also have positive influence on maternal survival, as found among the Finnish Sami where the number of daughters raised to adulthood was positively associated with maternal post-menopausal lifespan (Helle et al 2002). This association was suggested to be owing to the family system of Sami, where mainly daughters helped their mother in everyday household tasks (Helle et al 2002).…”

“…In some societies, males are the gender co-habiting with the ageing parents and thus primarily responsible for the well-being of the elderly, resulting in the more sons surviving, the better is the late-life survival of their parents (Omar Rahman 1999). Since Cesarini et al (2009) do not provide any analysis to this respect, they are incapable of contrasting the potential biological and socio-cultural correlates of maternal longevity. Consequently, they fall short of replicating our previous findings on the Sami people.…”

“…First, our original analysis was based on 375 postmenopausal Finnish Sami mothers (Helle et al 2002), whereas the analysis of Cesarini et al (2009) included, at maximum, 930 Swedish Sami mothers (ranging from 304 to 930, depending on how confident they were on the ethnicity of the mothers). Based on their larger sample size and non-significant results, Cesarini et al (2009) seem to suggest that our findings were false-positive.…”