At 10:22 13/02/01 +0000, Dr. Mary Shaw wrote:
>Jim - some numbers for you. Rounded to whole numbers (below), for
>England and Wales, the life expectancy advantage of women over men has
>been noticeable since the 1840s. Average Life expectancy is now almost
>twice as long, and the gender gap twice the size.
Thanks for the figures - which are what I understood to be the case (for
most 'Western' countries). In fact, my understanding was (and I'm not sure
where it came from), was that a similar gender difference in 'average life
expectancy (at least in UK) had probably existed for centuries, perhaps
longer. As others have pointed out, this is not necessarily the case in
every country.
In terms of 'average life expectancy', one thing that often seems to get
overlooked is that mean values (as usually quoted) can be rather
misleading, since a fair proportion of the change in the mean has resulted
from a change in distribution of lifespans. In particular, dramatic
reductions in infant/child mortality and mortality associated with
pregnancy/childbirth have had a lot to do with the reduction in 'mean life
expectancy' in those last 160 years, but have probably shifted the median
far less. When I was delving into my ancestry, pawing over large numbers
of ancient 'death records' etc., it was striking that in the distant past,
although there were a lot of young deaths, there were also a lot of people
achieving 'very good ages'.
I therefore assume that if one looked at the average life expectancy of
people of age, say, 35 or 40 (or, to some extent, even 15), one would see
much less of a change over the past century or two.
Returning to the point that Jim raised about screening, as you have said,
the gender-difference in life expectancy long pre-dates any formal health
screening (or the ability to do anything about results of screening), so
clearly cannot be an appreciable part of the explanation. Furthermore,
there is the sad, but true, fact that the benefits (in terms of survival)
of the major screening programmes (e.g. breast and cervical cancer) have
been pretty marginal. They obviously result in some increase in average
period of 'survival from diagnosis' (since diagnoses are occurring
earlier), but the average effect on 'age at death' is, to say the least,
disappointing. It seems that, for many women, early detection of breast
cancer does not appreciably delay their death, but does extend the period
during which they 'suffer' from the knowledge that they have the disease -
so, with presently available treatments, there is certainly scope for
debate about the value of screeniong.
As for why 'men have not got prostaic cancer screening' (at least, in the
UK) one of the main reasons is that we haven't got much of a clue as to
what to do about 'positive screening results', nor whether it would have an
appreciable impact on survival, or quality of survival.
Moving back even further in the discussion, to the question of what causes
the gender differences in 'average life expectancy' (from birth), a little
bit of that is, again, probably a 'statistical quirk', since the increased
neonatal/ infant mortality in males, and (I believe) the increased level of
traumatic/ violent deaths in young males, will 'pull down the mean' - so,
again, I suspect that the median might show less of a gender difference.
In biological terms, one imagines that a major factor is the fact that
women are largely protected ('by their hormones'), up to the time of the
menopause, from the arterial disease (leading to heart attacks and strokes
etc.) that are major killers in men from middle-age onwards; women have a
distinctly 'late/slow start' in that disease process. Beyond that, one can
but speculate. It is tempting to just 'blame genes' - not the least
because I think (but am not certain) that similar gender differences in
'life expectancy' are also seen in many other animal species.
Kind Regards,
John
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