Question of the Week

Why do women live longer than men?

Sat, 16th Jun 2012

Part of the shows Why Do I See Stars when I Stand? and Why do women live longer than men?

Question

Steven Wasmer asked:

Hello Dr's!

 

We've all heard that women on average live longer than man. My question is, ignoring any outside influences like smoking, risk taking, eating habits etc, is there any fundamental difference between the longevity of the male vs. female body?

 

Steve

Answer

We put this question to Dr. Claudia Langenberg from Cambridge University...

Claudia -   The short answer is that the definitive reason is unknown.  Menís death rate exceed womenís at all ages even early in life.  And the more likely and complex answer is therefore, that a combination of biological as well as behavioural and social differences contribute to the sex difference in life expectancy.  One factor that is likely to play a major role is the advantage that women have from being protected from so-called male diseases such as cardiovascular disease, which they had lower risk of and are getting later in life, even considering their on average healthier lifestyle.  Sex differences in longevity exists in almost all wild animal species.  And because the lifespan of a species is correlated with the duration of time that the offspring depend on their parents, some have argued that evolution favours maternal longevity.  This does, of course, not mean that keeping your children at home will make you live any longer.

Old lady from Zacatecas, MexicoHannah -   So, women may be protected from male diseases in order to help raise the next generation.  But what could be the biological mechanism behind this?  We zoom into cells with Dr. Emma Barrett from the University of East Anglia.

Emma -   The lifespan of our cells is at least partly determined by things called telomeres.  Like the plastic bits at the end of a shoelace, telomeres cap our strands of genetic material and protect the ends from fraying.  These telomeres get cut down in size each time a cell divides.  When the telomeres become too short, the cell can no longer replicate properly.  So instead of allowing the cell to misfunction and replicate in an out-of-control way, as weíre seeing in cancer, the short telomeres signal for the cell to commit suicide.

Although telomere lengths of babies are the same in both sexes, adult menís telomeres are on average shorter than womenís.  This sexual inequality in telomere loss appears to be because of the different hormones racing around male and female bodies.  Oestrogen is found in higher concentrations in women and seems to provide a degree of protection for telomeres.  Oestrogen reduces the effect that life stresses can have on shortening telomeres and may even promote telomere growth.  So womenís cells are better able to carry on replicating for longer than men because of their exposure to oestrogen.

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About 10% of the human genes are carried on the X Chromosome.
Women have 2 copies (1 from each parent), while men have only 1 copy (from their mother).
All chromosomes carry mutations, but a woman will have a second copy of the X Chromosome, which can mask defects on the the other one.
In the female, each cell randomly inactivates one of the X chromosomes, but the presence of two copies in the body is enough to reduce the chances of women suffering from "male diseases" like haemophilia. It probably also protects against a range of less-obvious conditions that could slightly shorten lifespan in males.
evan_au, Fri, 22nd Jun 2012

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