Three Associations that Offer Some Consolation

The discovery of associations between two conditions – say smoking and lung cancer - doesn’t prove anything.  For that you need a well-controlled prospective study, not just a snap-shot view.  However, it’s often enough to generate what’s called a “hypothesis for testing”, i.e. the reason for the prospective study.  Unfortunately, such a prospective study is often very difficult to design and carry out – think of the smoking/cancer problem.  This means that associations are often assumed to represent a cause (smoking) and an effect (cancer). With time, and more results, such a cause-and-effect relationship is generally accepted, and regarded as more-or-less proven.

Most medical associations involve two conditions, or a behavior and a condition, to provide a “risk factor” (the cause) for a disease.  Once in a while, there’s a report of an association where there’s an apparent protective effect of one condition on another.  Here are three recent examples.

First, there was a report that hot flashes were associated with a reduced risk of postmenopausal breast cancer.  Hot flashes (and other symptoms of menopause) are linked to reduced levels of estrogen; and estrogen in known to be linked to the occurrence of breast cancer. 

Second, the more allergies people have, the lower their risk of developing glioma, a malignant brain cancer.  Data came from 410 glioma patients and 612 cancer-free patients at Duke University and North Shore University Hospitals; the study is reported in CancerEpidemiology, Biomarkers & Prevention .  Survey results showed that all types of allergies appear to be protective against both types of glioma – high- and low-grade – with reduced risk for those with more types of allergies.  Antihistamine use was without influence on this. 

Finally, it seems that obese women are less likely to develop glaucoma.  This is based on a rather surprising finding in an analysis of Rotterdam Study data coming from the Netherlands, and published in the Archives of Ophthalmology online.  The population-based study included subjects 55 and over living in the suburbs of Rotterdam, who were free of open-angle glaucoma at the start of the study.  Over the next 10 years108 participants (2.7%) developed the condition. This group was significantly older, more often male, and more often nearsighted (myopia) than those without glaucoma.  In the women, there was a significant association between increased body mass index (BMI) and raised intraocular pressure (pressure within the eye).  However, each one-unit increase in BMI was associated with a 7% decrease in the likelihood of developing open-angle glaucoma.  There were no such relationships in men, and other lifestyle-related factors (socioeconomic status, smoking, and alcohol) were not associated with glaucoma in either sex. 

These three associations may offer some consolation to the victims of one of the conditions involved.  More beneficial, in general, is the hope that they will reveal a mechanism that can help explain the causation, and hence a route to prevention, for the more serious condition of the two.  In the first case, a possible mechanism is given; this is not yet available for the second and third cases.