Low thyroid without symptoms increases heart risk

By Megan Rauscher

NEW YORK (Reuters Health) – The results of a study of older
adults suggest that people who have an under active thyroid, or
hypothyroidism, but with no symptoms, have an increased the
risk of congestive heart failure, but not other cardiovascular
disease or death.

Asymptomatic hypothyroidism is characterized by an
increased level of thyroid stimulating hormone (TSH), but a
normal level of thyroxine (T4). The prevalence of this
condition increases with age, Dr. Nicolas Rodondi from the
University of Lausanne, Switzerland and colleagues explain in
the November 28th Archives of Internal Medicine.

Asymptomatic hypothyroidism has been associated with higher
levels of some cardiac risk factors but data on cardiovascular
outcomes and death are limited, they also note.

Rodondi’s team therefore examined the risks of heart
failure, coronary heart disease, stroke, peripheral artery
disease and death compared with TSH levels in a 4-year study of
2,730 men and women between 70 and 79 years old.

Hypothyroidism was detected in 338 (12.4 percent) of study
participants.

Compared with adults with normal thyroid function,
congestive heart failure was about twice as common in patients
with moderate or severe asymptomatic hypothyroidism.

The researchers defined moderate asymptomatic
hypothyroidism as a TSH level of 7.0 to 9.9 mIU/L and severe
asymptomatic hypothyroidism as a TSH of 10 mIU/L or greater.
Compared with study participants with normal thyroid function,
older adults with TSH levels of 7.0 mIU/L or higher had a two-
to three-fold increased risk of congestive heart failure. The
rate of new or recurrent heart failure was also increased in
this group.

Heart failure was not increased among those with TSH levels
between 4.5 and 6.9 mIU/L, which indicated mild asymptomatic
hypothyroidism.

The condition was also not associated with an increased
risk of coronary heart disease, stroke, peripheral arterial
disease, or cardiovascular and total mortality.

In comments to Reuters Health, Rodondi noted that the
results need to be confirmed by other large studies and in
younger patient populations. It also remains to be seen if
symptomatic hypothyroidism causes or worsens heart failure that
is pre-existing.

It’s still controversial, Rodondi added, whether screening
and treatment of asymptomatic hypothyroidism is advisable
because the current evidence is limited by the small number of
large studies that have been conducted.

In a related editorial, Dr. Lawrence M. Crapo of Santa
Clara Valley Medical Center in San Jose, California, says that
this study supports the idea that treating severe cases of
asymptomatic hypothyroidism with levothyroxine in patients
younger than 80 years may be helpful, but this need to be
confirmed in a therapeutic trial.

SOURCE: Archives of Internal Medicine, November 28, 2005.