1996
Why NIOSH Did the Heart Disease Study
We were concerned that two chemicals used at the Arsenal,
dinitrotoluene (DNT) and nitroglycerin (NG), caused heart
disease. We knew that NG swells blood vessels. When the workers'
NG levels dropped while away from work, their blood vessels
may have tightened. This may have caused some workers to have
chest pains or heart attacks.
Thus, the heart disease part of the study looked at heart attack
deaths in employees who "actively" worked with NG.
We define "actively" exposed to NG as having worked
with NG within the last 30 days.
Other studies have reported that workers who used NG or DNT for
many years also had an increased risk of heart attacks. Hence,
we also looked at heart attack risk in employees who have
worked with DNT or NG for many years.
How NIOSH Did the Heart Disease Study
We examined the records of all workers who had worked more than
5 months at the Arsenal. We classified people who
worked either in the double-or triple-base lines that used
NG as having worked with NG.
Employees who worked on the single-base line, which used DNT, were classified
as having worked with DNT.
We studied three groups of workers:
- 5,529 men who worked with NG,
- 4,989 men who worked with DNT, and
- 5,136 men who worked with neither NG nor DNT.
2,512 men who worked with both NG and DNT were included in both
groups 1 and 2. If we did not know whether you used DNT or
NG, we excluded you from the heart study.
Records
This study was done without contacting the individual worker because
it was based on records. It included living and deceased workers.
Government records were used to find out which workers had died. Death
certificates reported the cause of death.
NIOSH used public records to find out the death ratefor certain
diseases in the general public.
We calculated the number of deaths from each disease that
we would expect to find in the workers, based on the death
rates for these diseases in the entire U.S. population.
If the number of deaths from a disease in exposed workers is
higher than the expected number, then NG or DNT exposures
may be the reason.
We also compared death rates among different groups of workers.
Results
We compared employees exposed to NG to workers without any exposure
to NG or DNT.
- Before 1970, workers who were actively exposed to NG had about
twice the normal risk of a sudden heart attack.
- After 1970, this risk was reduced to normal.
- The risk of heart attacks was 3 1/3 times higher in workers
under 45 years of age who actively worked with NG.
There were 8 deaths among workers younger than 45 from heart attacks.
Only one of these deaths occurred after 1970.
Three factors may have combined to lower these risks after 1970.
- Workers with signs of heart disease or high blood pressure on medical
tests were not allowed to work with NG.
- Exposures to NG have been lowered.
- Medical treatment for heart attacks has improved in recent
years. Thus, more patients with heart attacks may have survived.
We compared workers exposed to NG or DNT to all unexposed workers.
Other studies suggested that we might see an increase in heart attacks
in employees exposed to NG and DNT for more than 5 years.
- However, we did not see an increased risk of heart attacks in these
workers.
- The workers who had worked less than a year with NG and
DNT had the highest risk of heart disease.
The likely reason for these findings is that the Arsenal
tested workers exposed to NG and DNT frequently for heart
disease. If you worked with NG, they examined you every six
months. If you worked with DNT, you were examined once a year.
They transferred workers who had signs of heart disease or high
blood pressure to jobs without NG or DNT exposure. Those who
worked for more than 5 years with DNT or NG had to pass many
heart disease tests.
Hence, those who had worked for more than 5 years were likely to
be healthier than those with less exposure.
Thus, it is not surprising that we did not see an increased risk
of heart disease in workers with long-term exposure to DNT
and NG.
If the DNT- or NG-exposed workers had not been tested so often,
we may have seen an increase in heart disease in these long-term
workers.
Other Findings of the Heart Disease Study
NIOSH also found an increased risk of accidents, violence, and mental
illness mostly due to alcoholism.
These increased risks occurred in all three groups studied and,
thus, were not related to exposure to NG or DNT.
In unexposed workers, we also found an increased risk of chronic
lung diseases usually related to smoking or to coal mining.
We found 34 deaths but expected only 21. We do not know the
cause of this increase.
We do not believe that workers who still work with NG have an
increased risk of fatal heart attacks.
However, if you work with NG and have chest pains, call your doctor,
911 or Emergency Medical Services immediately.
The fact sheet Steps to Protect Your Health has further information
on the symptoms of a heart attack.
If you have any questions or want copies of the technical reports,
please call the NIOSH toll free number at 1-800-356-4674.