Mortality among Catholic nuns certified as radiologic technologists

Abstract

Background: Several studies have shown that Catholic nuns have a different mortality experience than women of similar age in the general population. We had a unique opportunity to evaluate mortality patterns of nuns identified in an occupational study of nearly 145,000 radiologic technologists (73% female).

Methods: A total of 1,103 women were classified as nuns based on their titles of "Sister" or "SR". Their mortality experience was compared to other female radiologic technologists and to U.S. white females.

Results: Five hundred eighty-three nuns (53%) were deceased as of January 1, 1995. Compared to other technologists, nuns were at significantly increased risk of dying from all causes (Standardized mortality ratio (SMR)=1.1; 95% Confidence interval (CI)=1.0-1.2, stomach cancer (SMR=2.7; 95% CI=1.2-5.4), diabetes (SMR=2.2; 95% CI=1.0-4.1), ischemic heart disease (SMR=1.2; 95% CI=1.1-1.4), all digestive diseases (SMR=2.0; 95% CI=1.3-3.0), and gastric and duodenal ulcers (SMR=8.3; 95% CI=2.3-21.3). In contrast, we observed a significant deficit in lung cancer (SMR=0.5; 95% CI=0.2-0.9), no deaths from cervical cancer, and a breast cancer risk 10% lower than expected (SMR=0.9; 95% CI=0.6-1.3). When compared to U.S. females, nuns experienced significantly reduced mortality from all causes (SMR=0.8; 95% CI=0.7-0.9), cervical cancer (SMR=0.0; 95% CI=0.0-0.7), all endocrine, metabolic and nutritional diseases (SMR=0.5; 95% CI=0.3-0.9), all circulatory diseases (SMR=0.7; 95% CI=0.7-0.8) including ischemic heart disease and cerebrovascular disease, and all respiratory diseases (SMR=0.5; 95% CI=0.3-0.8), and a nearly significant deficit of diabetes (SMR=0.6; 95% CI=0.3-1.0). In contrast, nuns had an almost 3-fold greater risk of tuberculosis (SMR=2.9; 95% CI=1.4-5.3) and a 20% excess of breast cancer (SMR=1. 2; 95% CI=0.8-1.7). The breast cancer excess was concentrated among nuns first certified before 1940 (SMR=2.0; CI=1.3-3.0), when radiation doses were possibly the highest, but the risk did not increase with increasing length of certification.

Conclusions: Compared with the general population, the mortality experience of nuns was favorable and reflected the "healthy worker effect" commonly seen in occupational studies. Patterns observed for breast and cervical cancer possibly indicate differences in reproductive and sexual activities associated with belonging to a religious order. The possibility of a radiation-related excess for breast cancer among nuns certified before 1940 cannot be completely discounted, although there was no dose-response relationship with a surrogate measure of exposure (number of years certified). When their mortality experience was compared with other radiologic technologists, the influence of lifestyle factors was not apparent. Am. J. Ind. Med. 37:339-348, 2000. Published 2000 Wiley-Liss, Inc. dagger