Why do foreign-born adults have less heart disease than US-born adults?

Foreign-born adults living in the United States had a lower prevalence of coronary heart disease (CHD) and stroke than US-born adults did, according to an analysis recently published in Journal of the American Heart Association.

Foreign-born adults’ lower risk for these conditions could potentially be explained by the “healthy immigrant effect,” suggested researchers led by Jing Fang, MD, MS, Centers for Disease Control and Prevention (CDC), Atlanta, GA.

According to US Census data, the proportion of adults in the United States who were born in another country has almost tripled in the past four decades, from about 5% of the population (9.6 million) in 1970 to nearly 13% (40 million) in 2010.

Prevalence by birthplace

Studies by other researchers have shown that birthplace is linked to cardiovascular disease risk factors such as obesity, diabetes mellitus, and hypertension.

For this study, Dr. Fang and colleagues compared the prevalence of CHD and stroke among US adults by birthplace. They used data from the 2006 to 2014 National Health Interview Survey, a nationally representative survey of more than 260,000 US residents. They determined that 16.4% of US adults were foreign born.

After adjusting for select demographic and health characteristics, the researchers also found that age-standardized prevalence of both CHD and stroke were higher among US-born than foreign-born adults.

In particular:

• 8.2% of US-born men compared with 5.5% of foreign-born men reported CHD, while the prevalence of CHD was 4.8% in US-born women compared with 4.1% in foreign-born women.
• 2.7% of both US-born men and women had stroke compared with 2.1% of foreign-born men and 1.9% of foreign-born women.
• Compared with US-born adults, adults born in Asia, Mexico, Central America, and the Caribbean had lower prevalence of CHD.
• Compared with US-born adults, prevalence of stroke was lowest among men born in South America or Africa and women born in Europe.

Healthy immigrant effect

Could it be that foreign-born residents have fewer cardiovascular conditions because they haven’t (yet) adopted the notorious American diet and the generally sedentary lifestyle? A first pass at the data seemed to indicate just that: Foreign-born adults who lived in the United States longer than 15 years had a higher reported history of CHD and stroke than those in the United States for less than 5 years.

However, after Dr. Fang and colleagues adjusted for sociodemographic and health characteristics, this relationship was no longer significant. Indeed, data show that most countries of Europe, Asia, and Africa actually have higher CHD or stroke mortality than the United States, the researchers noted.

But if that’s the case, why did the researchers’ analysis find that foreign-born adults from these regions had an overall lower risk of nonfatal CHD and stroke than US-born residents?

“This could potentially be explained by the ‘healthy immigrant effect,’ where those who decide to immigrate to another country are usually healthier than those left behind, attributable to either self-selection or physical/legal barriers to entering the receiving country,” Dr. Fang and coauthors wrote.

An additional explanation: The higher prevalence of CHD and stroke in US-born adults could be affected by other factors, such as increased diagnostic testing, treatment, and survival rates in this population.

Also, when the researchers further analyzed the data to account for the impact of race and ethnicity, they found that associations between birthplace and risk of CHD and stroke weren’t as strong. For instance, “the protective associations of birth in Mexico, Central America, the Caribbean, South America, or Asia did not persist when compared with US-born Hispanics or US-born Asians.”

However, several associations of lower risk did persist for foreign-born adults from certain regions. Dr. Fang and coauthors concluded that these findings may help target prevention efforts toward high-risk populations.

In a related editorial, Eduardo Sanchez, MD, MPH, Chief Medical Officer for Prevention, American Heart Association, wrote: “As our overall population grows and becomes more diverse, knowing which groups have higher risk of disease can help guide our efforts to give all Americans—regardless of their birthplace, race, ethnicity, or other descriptive characteristics—the same opportunity to improve their health and prevent disease.”