A collaborative study has shown that people exposed to an H1NI strain of influenza A were significantly more likely to develop cardiovascular disease later in life. The researchers assessed more than 100,000 individuals born during and around the time of the 1918 flu pandemic in the US.
"Our point is that during pregnancy, even mild sickness from flu could affect development with longer consequences," said senior author Caleb Finch, USC professor of gerontology and biological sciences.
The study's authors write that after first appearing in the spring, and all but disappearing in the summer, the 1918 flu pandemic "resurged to an unprecedentedly virulent October-December peak."
They point out that the outbreak of influenza A, H1N1 subtype killed two 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. Prospective moms should reduce risk of influenza by vaccination," said Finch, director of the Gerontology Research Institute at USC.
According to the researchers, men born in the first few months of 1919 - 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, they say, 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.
However, the researchers add, women born in the second quarter of 1919 - first trimester during the height of the epidemic - were 17 percent more likely to have heart disease than the general population in later life.
Examining height at World War II enrolment for 2.7 million men born between 1915 and 1922, the researchers found that average height increased every successive year, except for the period coinciding with in utero exposure to the flu pandemic.
The team say that 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.
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," said Eileen Crimmins, professor of gerontology and sociology at USC.
"The lingering influences from the 1918-1919 influenza pandemic extend the hypothesized roles of inflammation and infections in cardiovascular disease from our prior Science and PNAS articles to prenatal infection by influenza," Crimmins added.
The study has been published in the Journal of Developmental Origins of Health and Disease.