|
Study Reports Smoking As Risk Factor For MS
Medical Update Memo
November 21, 2003
SUMMARY
Researchers in Norway have found that the risk of developing
MS is higher among smokers than in people who never smoked.
The investigators administered questionnaires that covered
current and previous smoking habits, including the age at
which smoking started, as well as if an individual had MS
and if so, when MS symptoms first started. The risk of developing
MS was nearly twice as high in people who were current or
former smokers compared to people who had never smoked. The
average duration from start of smoking to MS symptom onset
was 15.2 years. This is the second large, population-based
study to find an association between smoking and risk of
developing MS. A smaller, Montreal-based study also found
smoking was a risk factor for MS. Further study is necessary
to confirm this association and to explain the underlying
mechanisms for a possible link between smoking and developing
MS.
DETAILS
Researchers in Norway have reported that in a study of more
than 20,000 Norwegians, the risk of developing MS was higher
among smokers than people who never smoked. The study by
Trond Riise, PhD (University of Bergen, Norway) and colleagues
from Bergen University College and Harvard University was
reported in the October 28, 2003 issue of Neurology.
MS is believed to occur in persons who have
a genetically determined predisposition for the disease. But
evidence suggests that even those who are genetically susceptible
may need to encounter some other factor or factors in their
environment – infectious, environmental or dietary, for
example – in order for MS to develop. One environmental
factor that has been investigated is smoking.
Smokers have higher rates of lung cancer,
heart disease, emphysema and other respiratory problems, and
infants born to smoking mothers tend to have lower birth weight
than infants born to nonsmokers.
Several studies have examined the association
between smoking and the risk of developing MS, with mixed results.
Some smaller, hospital-based studies were negative, but a recent
large US population-based study of nurses found a statistically
significant association between smoking and risk of developing
MS. In Montreal, a small study examined a number of factors
that might be involved in the development of MS. People with
MS were 1.6 times more likely to have smoked prior to their
diagnosis than non-MS controls. The risk seemed to rise with
an increase in the amount smoked.
In Norway, the investigators administered
questionnaires and a clinical examination to 22,312 people
living in Hordaland, Norway. Questions covered current and
previous smoking habits, including the age at which smoking
started, as well as if an individual had MS and if so, when
MS symptoms first started. The development of other diseases
with which smoking has also been connected (heart attack, angina,
asthma) was also ascertained.
A total of 87 people reported having MS.
The risk of developing MS was nearly twice as high in people
who were current or former smokers compared to people who had
never smoked. The average duration from start of smoking to
reported onset of symptoms was 15.2 years. Separate from MS,
the risk among smokers for heart attack, angina, and asthma
was also increased – which, the authors say, supports
the validity of the association with MS.
This is the second large, population-based
study to find an association between smoking and risk of developing
MS. Further study is necessary to confirm this association
and to explain the underlying mechanisms for a possible link
between smoking and development of MS. However, there is increasing
evidence for a link between smoking and MS. Although there
is no evidence from this study that past or current smoking
can make MS worse in a person who has the disease, smoking
is known to produce shortness of breath, susceptibility to
lung infections, and heartbeat irregularities in many people.
These might transform a mild or moderate neurologic limitation
into a severe disability.
[Adapted from Research/Clinical Update,
National Multiple Sclerosis Society (USA)]
National Research Department
National Communications & Social Action Department
Click
here to view or print this bulletin in its
original format.
Disclaimer
The Multiple Sclerosis Society of Canada is an independent,
voluntary health agency and does not approve, endorse or
recommend any specific product or therapy but provides information
to assist individuals in making their own decisions.
|
