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Foreign-born US residents, with the exception of those born in Africa, are more likely to get a healthy amount of sleep than residents born in the States, according to a new public-health analysis. Researchers from the New York University School of Medicine and the University of Illinois looked at 10 years of nationwide data and found a relationship between birthplace and sleep duration. The study was published in the International Journal of Environmental Research and Public Health.  

Previous research has revealed sleep disparities across racial and ethnic groups. But there's a lot to learn about the way race/ethnicity and immigrant status interact. How does being born inside or outside the US statistically affect sleep (statistically) for people who are, for instance, European, Korean or Mexican? The current study authors sought to dive deeper into the impact of birthplace on sleep duration. To do this, they used data from the National Health Interview Survey (NHIS), a yearly CDC survey conducted through face-to-face interviews. The NHIS covers a wide range of health issues, including sleep duration, which is assessed through the question: "On average, how many hours of sleep do you get in a 24-h period?”

Participants who reported the healthiest sleep duration are part of immigrant groups that tend to live in "homogenous ethnic enclaves" after moving to the US.

The study took into account survey responses from 415,678 adults who participated in the NHIS between 2003 and 2013. About 16 percent of all participants were born outside the US, hailing from SE Asia, Asia, the Indian Subcontinent, the Middle East, Africa, Russia, Europe, South America and, collectively, Mexico, Central America and the Caribbean Islands. And, compared to those born in the US, they were more likely to be younger, be less educated and earn poverty-level incomes. They were also 19 percent more likely to get a healthy amount of sleep, defined as 7-8 hours a night — but the specific country of birth made a difference.

Participants born in Asia and on the Indian Subcontinent were most likely to report healthy sleep duration. Mexican-born participants were also slightly more likely (than US-born participants) to hit the sleep-duration sweetspot. Those born in Africa, however, did not report the same healthy sleep habits, and were significantly more likely to get too much or too little shuteye. Additionally, researchers found that living in the US for longer periods of time corresponded to less-healthy sleep across all foreign-born participants. 

The results of this study are somewhat consistent with trends reported in previous work. Michael Grandner, a psychologist at the University of Arizona who studies the relationship between sleep patterns and health, has found in his own large-scale analyses that, while low-income minorities overall tend to sleep poorly, low-income immigrants sleep pretty well. He calls it the "immigrant effect." And, across public health research generally, becoming an American tends to mean becoming less healthy. As Grandner told me last year:

We know that the more Americanized you get, the more unhealthy you become. It's something we see over and over. We start exporting culture around the world and all of the sudden, people start getting fat and having more diabetes and heart disease. There are benefits to the typical American culture, but one downside is that our culture is not very healthy.

The negative health impact of Americanization may help explain the results of this study: Participants who reported the healthiest sleep duration (those born in Mexico, India and Southeast Asia) are part of immigrant groups that tend to live in "homogenous ethnic enclaves" after moving to the US. This behavior may protect them against the poor health outcomes associated with American acculturation. Researchers, however, noted that they didn't specifically explore how the stress of acculturation affects sleep in foreign-born participants. But it's a worthwhile issue to take up in the future.

There's evidence that genetic ancestry influences circadian rhythms.

Study authors also considered how circadian differences, rooted in both biology and environment, might explain the results. There's evidence, they explained, that genetic ancestry influences circadian rhythms. In a few studies, for instance, people of African ancestry have exhibited shortened circadian cycles. This would manifest in earlier bed and wake times, as well as a decreased ability to adjust to seasonal periods of low light exposure and nighttime shift-work. "We argue that since Blacks on average tend to work longer days and are more likely to be nighttime shift-workers/forced night owls, they are therefore more likely to suffer from circadian misalignment which in turn affects their total sleep time," study authors wrote. 

Environmental circadian factors may also play a role in the healthy sleep duration reported by foreign-born participants from regions near the equator. As a result of exposure to high levels of sunlight, researchers explained, their circadian rhythms would be closely synched to daily dark-and-light cycles. This might make them resilient to the sleep-related effects of moving to the US.

But it's also worth mentioning the possibility of flawed data affecting the findings. A lot of sleep-health studies are based on self-report, meaning that participants rate how much and how well they sleep. In a formal research environments, Grandner suggested, foreign-born residents may feel pressure not to complain, and thus be less likely to rate their sleep as poor. The current study authors brought up the same issue, writing that "...foreign-born respondents may think it is more socially desirable to report more or less sleep duration and we were not able to adjust for these effects.