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Tobacco
Biggest Single Cause of Cancer
LONDON
(Reuters) - Many of the world's six million cancer deaths each
year could be prevented if people stopped smoking and lost weight,
a leading British scientist said on Wednesday.
Tobacco is
the biggest single cause of cancer and accounts for more than
half of all cancer deaths in smokers. In non-smokers, 10% of cancer
deaths in America and 7% in Europe are linked to being overweight.
``In terms
of public health, the most important aspect is smoking. If you
give up smoking, even late in life, it will have a big effect
on mortality,'' Professor Julian Peto told a news conference.
The epidemiologist
at Britain's Institute of Cancer Research and the London School
of Hygiene and Tropical Medicine conducted an overview of the
major causes of cancer discovered during the past 50 years. His
research is reported in the science journal Nature.
Because tobacco
is such a major risk factor, Peto divided people into smokers
and non-smokers to determine what causes the major types of the
disease.
``About 60%
of all cancer deaths in smokers are caused by smoking, and smoking
causes as many deaths from other diseases as it does from cancer.
It is absurd for smokers in the West to worry about anything except
stopping smoking,'' he said.
LUNG CANCER
Peto estimates
up to three-quarters of cancers in smokers can be avoided if people
quit, and the sooner the better.
Smoking is
the leading cause of lung cancer and also contributes to stomach,
liver, cervical, pancreatic, bladder and kidney cancers.
The cancer
picture is not as clear in non-smokers, but Peto said he was surprised
that being overweight had such an impact. Scientists aren't sure
of the mechanism through which excessive weight increases the
risk of the disease or if it can be reduced if people lose weight.
``There is
now a consensus that cancer is commoner in those who are overweight.
The evidence on weight is strongest for post-menopausal breast
cancer and cancer of the endometrium (lining of the womb), gall
bladder and kidney,'' Peto said in the Nature paper.
Infections
and a weakened immune system are other known risk factors for
cancer, along with excessive alcohol, sunlight and pollution.
Helicobacter
pylori, a bacteria linked to ulcers and stomach cancer, and the
human papilloma virus found in most cervical cancers are among
infections that contribute to about 15% of cancers.
Doctors also
suspect childhood leukaemia is triggered by an infection, but
scientists have not pinpointed the cause.
``Viruses
are particularly important in the developing world. Hepatitis
B virus, which can be prevented by vaccination, causes almost
as many cancers as smoking does in China,'' said Peto.
Genetic susceptibility
is also a risk factor in many types of cancer, but Peto added
that most of the genes involved remain to be discovered.
Reference
Source 89
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