Science is great at finding new rules for expectant mothers.  They already can’t have alcohol, caffeine, or cigarettes. They also need to stay away from their cat’s litterbox, stay off of planes and rollercoasters, stay off of antidepressants, drop their acne medication, and forgo even a well-considered vegan diet.

Now they have to avoid the Hong Kong flu, too.  The Annals of Neurobiology recently published a study that suggested that exposure to the Hong Kong virus during the first trimester of pregnancy may contribute to decreased adult intelligence.  

The Hong Kong flu is fairly easy to avoid now.  But it was everywhere in 1969 and 1970.  It reached its Norwegian apex in the spring of 1970, affecting up to 40% of the population.  

Until that time Norway had been enjoying a steady trend of increased adult intelligence. Children could expect their younger siblings to be, on average, a wee bit smarter.  But children born in September, October, and November of that year—in other words, children born 6-9 months after the epidemic’s major surge—lagged.  

Trouble is, it’s hard to put the relationship between intelligence and the Hong Kong flu into its proper perspective.  The authors hypothesize that all flu cases in the first trimester cause an epidemic of dumbing-down, not just the Hong Kong virus.  It won’t be easy to tell unless more flu-intelligence studies materialize.  

And the intelligence score dip in 1970 births doesn’t tell us much about the specific cause. Is the virus itself linked to intelligence levels? Or was there some other correlation— poor nutrition during illness, a medication, the weather during flu season? Or did something else happen at the same time as the Hong Kong flu?  For example, this study does not address the possibility that Norwegian moms-to-be were just really sad about the death of gold-medalist Thoralf Glad.

One disturbing circumstance remains.  The Norwegian baseline intelligence took a hit for those born in 1970, but it got back on track quickly.  After the years of the Hong Kong virus, Norwegian intelligence returned to its normal growth.  Clearly we still need to ready ourselves for the generation of Norwegian genius masterminds that are scheduled to take power around 2060.

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Willy Eriksen, Jon M Sundet, Kristian Tambs. "Register data suggest lower intelligence in men born the year after flu pandemic".  Annals of Neurology. (2009) 9999: 999A

Interesting related reading: The Flynn Effect explains all the smart Norwegians.  Apparently our grandparents were, on average, retarded.  Who knew?