“Constantly being sick as a baby/toddler or not” does seem like the sort of thing that could make a few IQ points worth of difference. Some things I found with Claude on a quick initial search:
This study found that a single infection resulting in hospitalization before the age of 19 was associated with an IQ 1.76 points lower at age 19, which shrunk to 1.13 points after adjusting for some confounders. They also found that the effects of these severe infections stacked, moreso if subsequent infections were of different types.
This one found that a single infection resulting in hospitalization before the age of 13 was associated with an IQ 1 point lower at age 18; 1.61 points lower if the infection was before the age of 1. The effects shrunk a lot after the age of 1: −0.7 points for ages 2-4, −0.26 points for ages 5-9, −0.12 points for ages 10-13. These effect sizes come from a model controlled for some confounders.
Another studyfound that having had any acute respiratory illness (ARI) before age 1 was associated with a 3 point lower Bayley score at age 1, but any ARI before age 2 was not significantly associated with score at age 2. (The Bayley is basically an IQ test for babies. If done at age 2 it probably correlates with adult IQ at something like r=0.3; even less if done at age 1.)
A study with a negative result: infections recorded between birth and age 5 were not significantly associated with IQ at age 11.
(Note: these could have been selected for positive results, either through publication bias or Claude searching.)
“Constantly being sick as a baby/toddler or not” does seem like the sort of thing that could make a few IQ points worth of difference. Some things I found with Claude on a quick initial search:
This study found that a single infection resulting in hospitalization before the age of 19 was associated with an IQ 1.76 points lower at age 19, which shrunk to 1.13 points after adjusting for some confounders. They also found that the effects of these severe infections stacked, moreso if subsequent infections were of different types.
This one found that a single infection resulting in hospitalization before the age of 13 was associated with an IQ 1 point lower at age 18; 1.61 points lower if the infection was before the age of 1. The effects shrunk a lot after the age of 1: −0.7 points for ages 2-4, −0.26 points for ages 5-9, −0.12 points for ages 10-13. These effect sizes come from a model controlled for some confounders.
Another study found that having had any acute respiratory illness (ARI) before age 1 was associated with a 3 point lower Bayley score at age 1, but any ARI before age 2 was not significantly associated with score at age 2. (The Bayley is basically an IQ test for babies. If done at age 2 it probably correlates with adult IQ at something like r=0.3; even less if done at age 1.)
A study with a negative result: infections recorded between birth and age 5 were not significantly associated with IQ at age 11.
(Note: these could have been selected for positive results, either through publication bias or Claude searching.)