Across my past three posts, I have been trying, with little success, to find evidence for the claim made in the Wall Street Journal that “sharing a bed is good for your health.” In this final post on the topic, I’ll take one last dive into original sources to see if I can find any good evidence for those elusive health benefits of sharing a bed.

Part 1 is here.

Part 2 is here.

Part 3 is here.

The study I most wanted to read this time was described in the Journal this way:

 “In one of Dr. Troxel’s studies, published in 2009, women in long-term stable relationships fell asleep more quickly and woke up less during the night than single women or women who lost or gained a partner during the six to eight years of the study.”

I searched the PsycInfo database of journal articles, looking for anything authored by Wendy Troxel in 2009 that mentioned sleep anywhere. I found just one article. The participants were only married women. There were no single women and nothing was mentioned about gaining or losing a partner in the past six to eight years. So the study could not possibly be the basis for the claim quoted above, but I’ll tell you about it anyway.

The 1,938 married women included in the sample were drawn from a national study of mid-life women. The participants included Americans of various ethnicities, including African-Americans, Hispanics, Chinese, and Japanese as well as Caucasians.

The idea tested by the study was a straightforward one: Happily married women would report better quality sleep than less happily married women.

The women rated the quality of their current marital relationship on one 7-point rating scale. They also rated their typical sleep quality and answered questions about various sleep disturbances, such as having trouble falling asleep or staying asleep.

This was, then, a simple correlational study: Do women who rate their marital relationships as happier report better sleep than women who rate their marital relationships as less happy? It was not an experiment with random assignment. If the authors were to find a relationship, there would be no definitive way of knowing whether marital happiness caused better sleep, whether better sleep caused happier marriages, or whether some other variable accounted for both.

So was there a link between saying that you are happily married and saying that you sleep well? The answer was a clear “yes” only for the non-Hispanic White women. The results for the African-Americans trended in the same direction. That was it. As the authors noted, “there was no evidence or even a trend toward an association between marital happiness and sleep disturbances in the Hispanic or Chinese women.”

Remember, the Journal’s claim was that there are health benefits to sleeping together. There was no measure of health in this study, and no comparison of sleeping together or not.

Notice the emphasis in the Wall Street Journal articles, as well as in this particular study, on marital relationships. Maybe it seems obvious that the relationships in question would have to be marital ones (or at least sexual ones), since the question is about sleeping separately vs. apart. However, not all of the studies compared sleeping separately vs. alone.

In the marital happiness study, for example, why look only at the quality of the marital relationship? Maybe sleep quality is also affected by the quality of your relationship with your best friend or your closest relative or whomever you consider to be one of the most important people in your life.

The authors believe they have that possibility covered. Participants were asked whether emotional and instrumental support was available to them. Their answers did not correlate with their reports about the quality of their sleep. To me, those questions do not seem equivalent to asking directly about the quality of your relationship with particular other persons.

I think the authors conceded that relationships other than the marital one might matter, too, when they speculated about why their prediction was not supported among the Hispanic or Asian women. The findings, they said,

“are consistent with prior research that suggests relatively greater emphasis on broader kinship ties, in Hispanic and Asian populations, compared to the traditionally Western emphasis on the marital relationship per se.”

There were a few other studies mentioned in the Wall Street Journal articles, and I looked at those, too. I found no evidence for the causal claim that sharing a bed results in better health.

Having written four posts tearing apart the claim about the health benefits of sharing a bed, now I want to acknowledge that sharing a bed may in fact have health benefits for some people. I haven’t found a rigorous study that documents that causal claim, but I would not be surprised if someday, some such evidence were produced, for some people.

Now let me explain what I’m still not convinced of. Some single people who are not in a romantic relationship say that they prefer not to share a bed. Some married people say the same thing. I don’t believe that the majority of those people are deluded. I don’t think that if you nudged them to share a bed, they would end up happier and healthier.

It is an empirical question. Once it is answered with compelling scientific data, then I wouldn’t mind reading about the answer in the national press.