1918’s lessons point to prenatal flu exposure

USC (US)—Fetal exposure to the 1918 H1N1 strain of influenza A appears to increase the risk for cardiovascular disease later in life, a new study finds.

“Our point is that during pregnancy, even mild sickness from flu could affect development with longer consequences,” says senior author Caleb Finch, a professor at the University of Southern California.

Finch and a team of researchers looked at more than 100,000 individuals born during and around the time of the 1918 influenza pandemic in the United States. Their findings are published in the Journal of Developmental Origins of Health and Disease.

After first appearing in the spring and all but disappearing in the summer, the 1918 pandemic “resurged to an unprecedentedly virulent October-December peak,” the researchers write. The outbreak of H1N1 subtype influenza A killed 0.6 percent of the total population. Most people experienced mild “three-day fever” with full recovery.

“[The] 1918 flu was far more lethal than any since. Nonetheless, there is particular concern for the current swine flu which seems to target pregnant women,” notes Finch, the ARCO/William F. Kieschnick Professor in the Neurobiology of Aging. “Prospective moms should reduce risk of influenza by vaccination.”

The researchers found that men born in the first few months of 1919—the second or third trimester during the height of the epidemic—had a 23.1 percent greater chance of having heart disease after the age of 60 than the overall population.

For women, those born in the first few months of 1919 were not significantly more likely to have cardiovascular disease than their peers, pointing to possible gender differences in effects of flu exposure. But women born in the second quarter of 1919—the first trimester during the height of the epidemic—were 17 percent more likely to have heart disease than the general population in later life, according to the study.

In addition, the researchers examined height during World War II enrollment for 2.7 million men born between 1915 and 1922 and found that average height increased every successive year except for the period coinciding with fetal exposure to the flu pandemic.

Men who were exposed to the H1N1 flu in the womb were slightly shorter on average than those born just a year later or a year before, according to the study. The researchers controlled for known season-of-birth effects and maternal malnutrition.

“Prenatal exposure to even uncomplicated maternal influenza can have lasting consequences later in life,” says Eileen Crimmins, professor of gerontology and sociology at USC.

The research was supported by the National Institute on Aging, the Ellison Medical Foundation, and the Ruth Ziegler Fund. Researchers from the Federal Reserve Bank of Chicago, Columbia University, and the University of Chicago contributed to the study.

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