Hello to all mothers and fathers out there! Congratulations on your families and I hope that your children are all going to grow up to be movers and shakers in our world! You are nurturing our future as a species with your children, however have you ever wondered whether having a child has had an effect on your health? Lets take things a step further, have you ever wondered whether your child was a boy or a girl had an influence on your health? Seems like a nonsense question right? There can't possibly be any sort of link between these things! Or is there?

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Today we discuss research recently published in the journal Nature: Scientific reports titled "Offspring sex and parental health and mortality". Here the authors were looking at just that, the sex of a child, and the potential for adverse long term health outcomes for either parent.

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Number of Children And Mothers Mortality

Remember when we are talking about mortality, we are talking about our likelihood of death from any cause. One area of study where people were looking at the effect on peoples lifespans has to do with whether or not they chose to have children, and what effects the number of children raised, have on their long term health (and likelihood of death).

There have been a surprising number of studies looking into this idea and the data that has been generated thus far may actually be surprising to you. For instance one publication found that, throughout history, having more children was associated with lower mortality. However in analysis of modern women it found that was no longer the case, it was observed that women who had either no children or had more than four children had higher mortality (aka they were more likely to die). Unexpected right?

This article feels a bit depressing, so perhaps I will fill it with some cute babies to lighten the mood

The above referenced article isn't the only source of data pertaining to number of children and potential relationship to parental mortality either! There have been a few indicating that having more children may result in a shorter life for a parent in modern times. [3]. However these studies pertain to having a bunch of kids, having kids in general is still thought to increase lifespan (especially in that 1-3 child range). [4] (yet another example of moderation in life being important... shows up everywhere it seems).

Does Gender Of The Child Matter?

Prior research on the subject postulated that ... yeah it might, as odd as that may seem from a common sense standpoint! Researchers have postulated that boys, being more difficult to raise then girls, may end up causing extra stress on their mothers and lead to decreased lifespans for those mothers. [5]. This sort of idea has been supported by other publications, where it has also been reported that male children reduce longevity in mothers. [6] While others pour cold water all over it and don't observe any correlation between male children and longevity of mothers. [7]

There are a variety of both physical, and socioeconomic factors relating to this discrepancy, life is not black and white. The article we are going to discuss today was written to look a bit more into the potential associations of the sex of your child and whether or not it effects the mortality rates of either mothers or fathers or both.

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So How About Some Results From The Study We Are Actually Discussing?

So here we are looking at some plots depicting the "hazard ratio" for death from a cardiovascular event (like a heart attack or something of that nature ) with respect to the number of either male or female offspring had for both mothers and fathers. The first thing that I think we need to clarify is what "hazard ratio" refers to. Basically this is the rate at which someone is likely to experience a "hazard" (in this case cardiovascular trouble). If we are examining two groups of people and one group has twice the rate of heart attacks when compared to the other, then they would have a hazard ratio of 2 in that comparison.

In Figure 1 we see that the correlation between number of children has a U shape, where having two children results in the lowest hazard ratio regardless of whether those children were boys or girls. This trend is observable for both mothers and fathers, but is way more pronounced for mothers. What we can also see from this plot is that the increased likelihood of cardiac events with more children is much MORE pronounced for women who have had four or more male children. Odd right?

Other Results

• Having a boy as the first child was associated with higher risk of death (by 2%) in general in women but not in men, for men there was no association at all. Having a girl as the first child resulted in no change in mortality risk.
• The increase in mortality from having male children was mostly due to an increase in the chance for a cardiovascular related issue.
• For other diseases (non cardiovascular) a correlation was not observed

Why Might This Happen?

Why are these negative health outcomes so prevalent for mothers but not fathers? Its a good question. One such possibility could be due to the hormonal changes that women experience during pregnancy. These changes are not the same for a male and female child. The authors explain that for mothers higher levels of oestrogen and testosterone are associated with having male offspring. However having female children results in higher levels of progesterone and gonadotropins. [8].

It is entirely possible that the exposure to these differing hormone levels may effect the health of mothers down the road. This would also partially explain why the overall effect on the health of fathers (from number of children, shown in figure 1) is not as significantly affected as it is for mothers.

A Random Observation

The sample sizes used in this study are HUGE, they took into account data from over 600,000 women and 600,000 men. So over one million total data sets. That is a lot of information to parse through and analyze. It also produces a higher degree of credibility to the associations they pulled out, as they truly have to be present across a very significant number of people for it to not be swamped out by the sheer size of the population.

You made it to the end, so you've earned one more adorable baby picture

Closing Thoughts And Answering The Title Question

It is strange to me that there is this association between the gender of the children we have, and the potential for mortality of a mother. Yes the sex of a child affects a mothers future health, male children raise the chance of cardiovascular events (heart attacks etc. ). The idea that hormones during pregnancy may be involved is an interesting thought, but the whole concept is a bit unsettling to me. What do you think about all of this?

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Sources

1. https://www.nature.com/articles/s41598-017-05161-y
2. http://www.tandfonline.com/doi/abs/10.1080/00324720500436011
3. http://www.sciencedirect.com/science/article/pii/S1568163707000207
4. https://www.ncbi.nlm.nih.gov/pubmed/16510865
5. https://www.ncbi.nlm.nih.gov/pubmed/20299140
6. https://www.ncbi.nlm.nih.gov/pubmed/12004121
7. https://www.ncbi.nlm.nih.gov/pubmed/21551178
8. https://www.ncbi.nlm.nih.gov/pubmed/8776463

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