Abstract & Commentary
Synopsis: Married couples often share the same chronic diseases.
Source: Hippisley-Cox J, et al. BMJ. 2002;325:636-640.
Expanding upon their earlier study that demonstrated that spouses of hypertensive patients are more likely to be hypertensive themselves, these British researchers studied couples to determine whether other illnesses exhibited the same association. In particular, they chose to study depression, diabetes mellitus (DM), hypertension (HTN), ischemic heart disease (IHD), stroke (CVA), hyperlipidemia, peptic ulcer disease (PUD), and asthma or chronic obstructive pulmonary disease (COPD). They selected these conditions because they are common and important and because there are plausible explanations for why 2 people living in close and, presumably, intimate proximity might develop the same illness. For instance, Helicobacter pylori causes the majority of PUD, and family members of patients who are positive for H pylori tend to be colonized themselves.
Conducting a cross-sectional study over 10 general practices that are part of a collaborative research network, they identified 29,014 people aged 30-74 years. These practices use computerized records from which Hippisley-Cox and colleagues were able to extract diagnoses and prescription medications. The working definition of "married" was "2 individuals . . . living together at the same address; of different sex; and with the same surname, titles of Mr. and Mrs., and a difference in age of less than 15 years." The exclusion criterion was no other adults aged 30-74 years living in the same household. This yielded 8386 couples. After adjusting for age, body mass index, and smoking status, spouses of patients with asthma (odds ratio [OR], 1.69; 95% confidence interval [CI], 1.43-1.98), depression (OR, 2.08; CI, 1.71-2.54), HTN (OR, 1.32; CI, 1.04-1.67), hyperlipidemia (OR, 1.44; CI, 1.19-1.75), and PUD (OR, 2.01; CI, 1.49-2.73) were at significantly higher risk for the same diseases. DM (OR, 1.41; CI, 0.87-2.26), IHD (OR, 1.28; CI, 0.78-2.11), and CVA (OR, 1.21; CI, 0.71-2.07) had nonsignificantly higher odds ratios for those diseases.
Comment by Allan J. Wilke, MD
I love this study because it lends itself so well to unfounded and out-of-the-box speculation. For example, it wasn’t that long ago that we believed that PUD was caused by over-secretion of gastric acid. We now know, as conclusively as medical science will allow, that in most cases PUD is an infectious disease or related to nonsteroidal anti-inflammatory drug use. Additionally, there is mounting evidence that points to infectious agents as the cause of Type 1 DM and IHD. Beyond the adage, "If you walk out of the examining room feeling depressed, then your patient probably is too," what if depression were infectious, too?
There are multiple explanations for the associations in this study. Diet plays a role in DM, HTN, and hyperlipidemia, and it is not unreasonable to assume that couples may share the same diet. Shared environment (ie, allergens and atmospheric pollution) could explain the asthma association. It is possible that the "first-diagnosed" half of the couple influenced the subsequent diagnosis of the other. For example, a husband with diabetes might recognize the symptoms of DM in his better half. A wife with HTN could insist that her hubby be screened. And let’s not forget what Hippisley-Cox et al term "assortive mating"—that is, you might select a mate based on a life-style risk factor. Couples who smoke may be together because they enjoy this shared activity. That sort of non-randomization could explain the COPD.
Cross-sectional studies are the Rodney Dangerfields of evidence-based medicine—they just don’t get any respect. I think part of it has to do with the basic pragmaticism that underlies EBM. Cross-sectional studies are subject to selection bias ("who’s in, who’s out"). They produce associations, and you can’t apply associations to individual patient care ("Mrs. Johnson, I think you should file for divorce before you catch a bad case of depression!") without sacrificing some intellectual honesty. There is also a "which came first, the chicken or the egg" quandary: does alcohol cause depression, or do people treat their depression with alcohol? Are there any practical applications for this study? I think the results argue for screening the spouses of patients with asthma, depression, HTN, hyperlipidemia, and PUD for the same.
Dr. Wilke, Assistant Professor of Family Medicine, Medical College of Ohio, Toledo, OH, is Associate Editor of Internal Medicine Alert.
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