Just in case we needed another reason to push for a nationwide
day care program, epidemiologists in the UK have provided
one: regular attendance at day care in the first year
of life prevents acute lymphoblastic leukemia (ALL), and
possibly other cancers as well.
The leukemias are the most common
of childhood cancers, and between 1985 and 1992, accounted
for just over one-quarter of all malignancies in Canadian
youth. About 320 children and teens are diagnosed with
leukemia annually in Canada, with more boys being affected
than girls. Approximately three-quarters of childhood
leukemias are ALL, which arises in immature lymphocytes.
Advances in cancer therapies, mostly in the treatment
of ALL, have led to a dramatic drop of more than half
in childhood mortality since the 1970s.
VIRAL
CAUSE
Evidence points to higher risk in kids who are immunocompromised.
Clusters of ALL cases and the observation of a peak
in incidence between age two and three years has led
to the hypotheses that ALL is related either to improper
development of the immune system or is a response to
an infectious agent.
The intriguing suggestion that
infectious agents are responsible for childhood leukemia
dates from the 1940s, but it was really a 1988 paper
in The Lancet that provided the evidence, albeit
circumstantial. That study showed that an influx of
newcomers to an isolated area led to a spike in the
incidence of ALL among younger individuals, particularly
those under the age of five. In such an isolated situation,
"herd immunity . . . would tend to be lower than average,"
lead author Dr Leo Kinlen from Oxford University explains
in the article. He also suggests that "leukemia [was]
a rare response . . . to a postulated widespread virus
infection." Following this argument, kids in day care
may be protected from ALL as they're exposed to more
infectious agents, which build up their immunity to
a wider range of pathogens.
SOCIAL
CREATURES
In this new study published online April 22 in the British
Medical Journal, Clare Gilham and her co-authors
at Cancer Research UK's Epidemiology and Genetics Unit
tested the supposition that "reduced exposure to common
infections in the first year of life increases the risk
of developing ALL." They used attendance at day care
and social activity as proxy measures of infection exposure
in infancy, reasoning that increased socialization would
also increase contact with pathogens.
The kids enrolled in the investigation
formed part of the UK childhood cancer study (UKCCS).
About 3,000 children with cancer, almost half of them
with ALL, were compared with a control group of over
6,000 kids, aged two to 14. The authors found that "increasing
levels of social activity were associated with consistent
reductions in risk of ALL; a dose-response trend was
seen." A similar trend was seen for non-ALL malignancies.
BMJ published online Apr 22,
2005
|
