It’s not hard to imagine that when our distant ancestors began to band together for protection from predators, they probably slept better too (at least those who were on the inside of the tangle of sleeping bodies). A new study finds that all these years later, the link between sleep, society and survival remains fundamental: When we feel connected, we sleep better -- and very likely are better.

The study, published Tuesday in the journal Sleep, finds a direct link between our feelings of social connectedness and the unbroken quality of our sleep. In so doing, the authors offer new evidence to suggest that sleep may be the missing link in the well-documented relationship between loneliness and poor health (or, if you will, between social connectedness and good health).

A pioneering 2002 study was the first to draw a direct line between loneliness and sleep quality. But while that study tracked the relationship in the loneliest and least lonely segments of a population of college students, the latest study does so in a far more homogeneous group of subjects: members of the Hutterite religious communities of South Dakota. (Two of the 2002 study’s authors, the University of Chicago’s Louise C. Hawkley and John T. Cacioppo, participated as authors in the study published this week.)

The differences between the Hutterites and the 64 undergraduates studied in the 2002 effort could not be more stark. The college students were young and mostly lived apart from the families in which they grew up. Many smoked tobacco and consumed alcohol and were immersed in the rituals so common to young adults of trying out new identities and relationships. The Hutterites, members of a 500-year-old religious sect, live in tightly bound farming communities of about 150 people, where they routinely work, eat, socialize and worship together. Like many college students, the Hutterites drink a lot of coffee. But their strict religious tradition forbids alcohol and tobacco use. And their average age was about 40.

Still, even with Hutterites, loneliness happens. Asked to rate, on a scale of 0 to 2, how often they felt they lacked companionship, felt left out and felt isolated from others, even some Hutterite participants proved to feel imperfectly connected: Though the group’s average loneliness index of .69 was relatively low compared with other, larger populations measured, there were among the group some who reported feelings of loneliness despite being married and living among extended family.

But for all the differences that separated college undergrads from Hutterites, the relationship between loneliness and sleep quality held steady: For every additional increment of loneliness a Hutterite participant reported at the outset of the study, his or her sleep -- as measured over the next seven nights by a motion-detecting wristwatch called an actigraph -- was found to be more fractured by awakenings.

Researchers found no link between levels of reported loneliness and other measures of sleep, including the length of time that elapsed between falling asleep and morning awakening, subjects’ personal assessment of their sleep quality and subjects’ reported daytime sleepiness. While those measures of sleep quality are either subjective or unrevealing of actual sleep quality, the actigraph readings are actually a pretty good measure of sleep quality.

The current study’s findings appear to fill an unexplored gap between two newly fertile fields of research: One of those has found a clear relationship between loneliness and health; the other has drawn a direct and often causal link between poor sleep quality -- and specifically sleep fragmentation, with its frequent awakenings and “microawakenings” -- and ill health effects. Lonely people have been found to die earlier, to heal from wounds more slowly and to have higher rates of inflammation, which is tied to a host of chronic diseases. And dozens of studies in recent years have drawn links between poor sleep quality and metabolic disturbance, obesity, depression, memory problems and sleep apnea, and cardiovascular disease.

The Hutterite study may be the first step in providing the missing link between those two fields of research.

“It is plausible, therefore, that sleep fragmentation may be a link between loneliness and downstream health outcomes,” the authors wrote. “Sleep could be a pathway through which perceived social isolation influences health,” they added.