A recent review conducted by researchers at the University
of Lausanne, Switzerland, concluded that people who currently smoke face an
increase risk of developing type 2 diabetes compared to non-smokers.
Type 2 diabetes is often associated with excess body weight,
poor diet and sedentary lifestyle and is the increasingly common disease in
many countries, including Switzerland.
Carole Willi, M.D., of the University of Lausanne,
Switzerland, and colleagues reviewed 25 previous studies, published from 1992
to 2006, about the association between active smoking and the incidence of
diabetes or other glucose metabolism irregularities. The studies involved more
than 1.2 million people aged 16 and older.
Researchers found that 45,844 developed type 2 diabetes
during the studies, which lasted for 5 to 30 years.
"We knew a few studies had already assessed this link,
but we didn't expect to find so many -- we found 25 studies and all except one
showed that smokers faced an increased risk of diabetes," Carole Willi
said.
The analyses of the existing data indicated that active smokers
have a 44 percent increased risk of developing type-2 diabetes compared with
non-smokers.
Heavy smokers, meaning people smoking more than 20
cigarettes per day have 61 percent increased risk compared with lighter smokers
from which only 29 percent face increased risk. The review also found that
quitting smoking reduced the danger, with former smokers seeing a 23 percent
higher risk that non-smokers, far lower than the risk of current smokers.
Willi added that the studies cannot prove smoking was a cause
of diabetes, but she said they did meet several recommended criteria to suggest
this.
"First, there is an appropriate temporal relationship:
the cigarette smoking preceded diabetes incidence in all studies. Second, the
findings are consistent with a dose-response relationship, with stronger
associations for heavy smokers relative to lighter smokers and for active
smokers relative to former smokers? Third, there is theoretical biological
plausibility for causality, in that smoking may lead to insulin resistance or
inadequate compensatory insulin secretion responses according to several but
not all studies. Conversely, there are also possible non-causal explanations
for this association. Smoking is often associated with other unhealthy
behaviors that favor weight gain and/or diabetes, such as lack of physical
activity, poor fruit and vegetable intake, and high alcohol intake," the
researcher wrote.
The review of the studies doesn’t show whether exercise,
social class or education affected the results so the researchers recommended
further studies which should focus on those issues.
The review appeared in the December 12 issue of The Journal
of the American Medical Association
