Potential conflict of interest: Nothing to report.
Register data suggest lower intelligence in men born the year after flu pandemic†
Article first published online: 18 MAR 2009
Copyright © 2009 American Neurological Association
Annals of Neurology
Volume 66, Issue 3, pages 284–289, September 2009
How to Cite
Eriksen, W., Sundet, J. M. and Tambs, K. (2009), Register data suggest lower intelligence in men born the year after flu pandemic. Ann Neurol., 66: 284–289. doi: 10.1002/ana.21702
- Issue published online: 1 OCT 2009
- Article first published online: 18 MAR 2009
- Accepted manuscript online: 18 MAR 2009 12:00AM EST
- Manuscript Accepted: 6 MAR 2009
- Manuscript Revised: 23 FEB 2009
- Manuscript Received: 13 NOV 2008
To test the hypothesis that prenatal exposure to the Hong Kong flu, an influenza pandemic that haunted Europe during winter 1969 to 1970, was associated with reduced intelligence in adulthood.
Data from the Medical Birth Register of Norway were linked with register data from the National Conscript Service. The sample comprised all registered boys born alive in single birth after 37 to 43 weeks' gestation during 1967 to 1973 (n = 205,634). Intelligence test scores, recorded at military conscription, were available for 182,913 individuals.
The mean intelligence score increased from one birth year to another, except for a downturn in 1970. The birth year 1970 was inversely associated with intelligence score (−0.03 standard deviation [SD]; p < 0.001) after adjustments for birth characteristics, parental characteristics, and the trend of increasing scores over the 7 birth years. Analyses with the sample stratified by birth month showed that the inverse association between the birth year 1970 and intelligence score was significant only among men born in July (−0.04 SD; p = 0.049), August (−0.05 SD; p = 0.013), September (−0.09 SD; p < 0.001), and October (−0.06 SD; p = 0.008). Thus, the intelligence scores of the men born 6 to 9 months after the epidemic were lower than the mean values for the men born in the same months a few years before or after.
Early prenatal exposure to the Hong Kong flu may have interfered with fetal cerebral development and caused reduced intelligence in adulthood. Ann Neurol 2009;66:284–289