Occupation and cancer - European Trade Union Institute (ETUI)

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reproductive organs in women. The risk of breast
cancer decreases with increasing parity, in particular
if the first birth is below the age of 20 [186]. The risk
of endometrial cancer decreases with increasing
parity, in particular if the age of the last birth is
above 35 years [100]. The risk of ovarian cancer
[187] is also decreased with increasing parity without
connection to ages at deliveries [188].
In general, women in higher socio-economic
classes have lower fertility rates. In Norway, for
example, the average age at first birth in occupations
that require high education, such as dentists,
physicians, and teachers, is about 5 years higher
than in occupations with short education (Table 87).
The average number of children was highest among
farmers, gardeners, and fishermen, while otherwise
the variation was not very large. The percentage
of nulliparous women was highest among seamen
and journalists and also the parous women in these
categories had few children on average.
There are similar data in Finland from 1985,
including women in ages 40 49 [6], showing similar
fertility patterns as the Norwegians. For instance
the proportion of nulliparous journalists in Finland
was 23% (Norway 27%) and average number of
children among the parous was 2.0 (Norway 1.5).
For farmers, the proportion of nullipara was 7%,
and the average number of children was 3.0 in both
countries.
In Iceland, record linkage was done between the
Census and the population-based Cohort Study of
the Cancer Detection Clinic, where information on
reproductive factors has been collected since 1964
[189]. This was done as a preparatory phase of the
future analyses of the NOCCA project, where parity
data are required as cofactors in multivariate analysis
on occupational risk factors of hormone-related
cancer sites. The average age at first birth among
Icelandic women born in 1935 1950 was 21.8 years,
i.e., about two years younger than in Norway, but
the differences between the occupations with the
oldest age at first birth (physicians, 26.2 years) and
the youngest age at first birth (B21 years, e.g.,
among shop workers, gardeners, fishermen, shoe
and leather workers, printers, food workers and
launderers) was similar as in Norway. The average
number of children was 2.5 among physicians, but
between 3.1 and 3.7 for the other occupations
mentioned above.
In a sample of Danish married women aged 15 49
years and interviewed in 1970, 23% of women with
7 9 years of education reported birth of the first
child before age 20, whereas this was the case for
only 2% of women with 12 or more years of
education [190]. The fertility differences were relatively
small among Swedish women born in 1940
Occupation and cancer in Nordic countries 779
1949, with women with only basic education having
on average 2.1 children and women with university
education having on average 1.9 children [191].
Occupations with high age at first birth systematically
had elevated SIRs for breast cancer in the
current study. In occupations where women had a
high number of children, the risk of breast cancer was
low. For cancer of the corpus uteri and for ovarian
cancer, the occupational variation in risk was small
and not clearly associated with the fertility pattern.
Socially discriminating cancers
The variation in relative risk across occupational
categories varied considerably between cancer
types. The cancer sites thus formed a hierarchy
from cancer sites with large variations to cancer
sites with small variations (Figure 51). For men,
mesothelioma topped the list with a 20-fold risk
variation between the lowest risk group of farmers
with an SIR of 0.24 (95% CI 0.21 0.28) and the
high risk group of plumbers with an SIR of 4.74
(4.18 5.38). In contrast, only a 1.5-fold risk variation
was found for multiple myeloma, where the
SIR varied from 0.79 (0.46 1.26) for laboratory
assistants to 1.31 (0.95 1.78) for launderers.
The risk variation was large for cancer sites where
work-related exposures play a marked role. This
was the case for mesothelioma, where the asbestos
exposed plumbers came out with the highest risk for;
lip cancer; where the sunlight exposed fishermen had
the highest risk; and for cancer of the nose, where
the wood dust exposed woodworkers topped the list.
In addition, large risk variations were found for
alcohol and tobacco related cancers. Risk variations
were 5-15-fold for cancers of the pharynx, oral
cavity, liver, tongue, larynx, oesophagus and lung.
Waiters topped the list on all of these seven cancer
sites, and farmers were at the bottom for six of them.
The SIRs for these occupational categories differ for
most cancer sites (Figure 52). Waiters had higher
incidence in most cancer sites than farmers, suggesting
that cancer-causing factors tend to cluster in
same population categories. The only exception
where farmers had a significantly higher incidence
was lip cancer among men. The risk variation
between the female waiters and farmers was smaller
than between male ones.
The cancer sites with less risk variation were
primarily those less attributable to specific established
aetiological factors related to occupational
exposures or social status. The variation among
men was about twofold for cancers of the testis,
pancreas, kidney, thyroid, colon and prostate and
non-Hodgkin lymphoma, and only about 1.5-fold
for cancers of the rectum, soft tissue, and brain, as