Smoking Could Increase Risk of Thyroid Disease
March 21, 2000 (Los Angeles) -- Need yet another reason to quit smoking? A
new study from Denmark shows a strong link between cigarette smoking and
thyroid disease. The authors say their analysis of 132 pairs of twins in which
one member developed thyroid disease and the other did not provides
"irrefutable" evidence of an association between smoking and thyroid
"This represents a new way of looking at the possible relationship
between smoking and thyroid disease," says endocrinologist Robert D.
Utiger, MD, who reviewed the study for WebMD. "The twin approach is a novel
Study author Thomas Heiberg Brix, MD, and colleagues at Odense University
and Odense University Hospital in Denmark studied 132 pairs of identical and
fraternal twins born from 1953 to 1972. The researchers found what they call
"a significant association" between smoking and thyroid disease. The
amount of tobacco consumption also was significant: In the 51 pairs of twins in
which both members smoked, tobacco use had been heavier in the twin who
developed thyroid disease.
Smoking was found to be associated with both overactivity and underactivity
of the gland. Symptoms of an overactive thyroid, which doctors call
hyperthyroidism, include heart palpitations, insomnia, fatigue, hair loss, and
a feeling of being hot most of the time. Symptoms of an underactive thyroid, or
hypothyroidism, include fatigue, weakness, muscle cramps, constipation, and
feeling cold most of the time.
In this study, smoking was most strongly associated with forms of thyroid
disease in which the patient's immune system attacks the gland as if it were an
invading organism. Utiger believes this might occur because smoking facilitates
the production of defense mechanisms against one's own body. Graves' disease,
one of the conditions that results from this phenomenon, is characterized not
just by an overactive thyroid but also by swelling and inflammation of the
muscles and tissues around and behind the eye, which cause the eyes to bulge,
Utiger says. Patients with this condition may see double because their eye
movements are no longer coordinated, and their eyes may tear excessively.
Earlier studies have demonstrated a relationship between smoking and all
kinds of thyroid disease, says Utiger, a clinical professor of medicine at
Harvard Medical School. "It is one of the mysteries of the topic, how
smoking can be associated with all of these conditions," he tells WebMD.
"In my opinion, there is no plausible explanation for why smoking is
associated with an overactive thyroid on the one hand and an underactive
thyroid on the other hand. It could be that smoking simply damages the thyroid
in general, and that damage expresses itself in different ways in different
individuals." Some evidence suggests that patients with eye problems
improve more quickly when they stop smoking.
Cigarette smoke affects so many different organs because it contains "a
whole carload of chemicals," Utiger says. "Nicotine, cyanide,
hydrocarbons -- there are a whole host of poisons, with effects on a variety of
tissues, rather than just one unifying poison." He believes the most
important message of this study is that "these data provide further
evidence that smoking is associated with several different kinds of thyroid
- A new study shows a strong association between cigarette smoking and
different types of thyroid disease.
- The cumulative effects of cigarette smoking were important, as those who
smoked more were more likely to develop thyroid disease.
- Researchers do not know how smoking can cause either overactivity or
underactivity of the thyroid gland.