It gets a bit trivial if you count deficiencies as improving IQ by "correcting" their dose. I would think any simple intervention doesn't really count as improving IQ so much as enabling some latent potential that was already present. We can also ingest less lead or get bashed on the head less, but once everyone's doing that perfectly, we'll still have people with lower IQ that can't be brought up to the level of those with the highest.