Læknablaðið - 01.06.1973, Blaðsíða 48

122
LÆKNABLAÐIÖ
We have thus in the environment added
substances or substances naturally occurr-
ing which can be sho'.vn to be associated
in excess with human disease or with ab-
ncrmalities in experimental animals. How
are we to decide what significance is to be
attached to animal findings?
There are more obvious environmentai
contaminants, like cigarette smoke, which
we know has adverse efíects on human
health in many different ways. Exposure
to blue asbestos, crocidolite, can produce
a highly specific form of malignant dis-
ease, mesothelioma, and we can exclude
it substantially from future use in con-
struction work. It is possible to show, as
Acheson has done, that there is some fac-
tor in certain processes in the boot and
shoe industry and in the furniture trade
which causes an unusual form of naso-
pharyngeal cancer many years after first
expcsure. The use of naphthylamine in
rubber processing has caused bladder
cancer in a substantial number of exposed
workers.
This sort of factor in the environment
sets an entirely new series of problems in
preventive medicine. The epidemiological
investigation in man is very difficult and
extrapolation from results in animais is
an uncertain method. In man carcinogenic
factors have usually been identified only
because of the very large size of the ef-
fect, as with cigarette smoking or a highly
specific and unusual form of malignant
disease as with chimney-sweeps cancer or
the cancers due to exposure to mineral
oil or the naso-pharyngeal cancers just
quoted. An experimental approach to such
investigations in man is out of the question
and so far as carcinogenesis is concerned,
in animals one has to use very large doses
because very long periods of observation
are not possible.
The time has come to ask ourselves
whether we are right in behaving as if
cancers due to environmental causes were
the exception. Dr Higginson of the Inter-
national Agency for Research on Cancer
has postulated that 80% of malignant dis-
ease is due to environmental factors. If
we could distinguish what those factors
are, it is highly unlikely that all of us
could avoid all of them, but we might be
able to reduce exposure to some or all
of them in varying degrees. There might
be efforts to reduce the effects of some
cf the exposures which are inevitable.
Known contributory factors in the de-
velopment of chronic respiratory or cardio-
vascular disease may be even more im-
portant. Sudden death from cardiovascular
disease has been shown to be more com-
mon in soft water areas than in hard
water areas and it is the same condition
that is commoner in cigarette smokers than
non-smokers. Chronic bronchitis is of
course substantially associated with cigar-
ette smoking but also with atmospheric
pollution. These degenerative conditions
are major factors in the process of aging.
One of the most exciting aspects of pre-
ventive medicine at the present time is
the number of clues pointing toward pos-
sible factors in the incidence of malignant
and degenerative conditions. They may
only be vague clues, but they suggest that
there may be definable and measurable
factors, some of which might then be cap-
able of modification. All this may caíl
for highly sophisticated systems of in-
vestigation, but the scope of epidemio-
logical studies on such subjects may be
extremely wide and dependent upon a
large number of contributors of small
pieces of information. At least automatic
data processing now given us the oppor-
tunity of bringing an infinite memory into
this, where previously the personal ex-
perience of any individual had to be short.
I have only given some examples of the
area that lies before us for investigation
and these could be multiplied on a scale
that would take far more time than I have
today.
I turn now to the area which has been
described as secondary prevention, the
early identification of disease or disability.
There are obvious examples of this in the
identification of congenital abnormalities.
Some of these are remediable if treated
at once as for instance imperforate anus
or tracheo-oesophageal fistula. Some are
obvious like spina bifida, but need careful
selection if treatment is not to be dis-
appointing. Some, like congenital dis-