Why do they say it or why would it be true?
I can't quickly find a reputable source to back up this claim. Some argue that any such relationship is weak, at best. But I'll assume it's true, for now.
Zinc and copper compete for some of the same chemical receptors in the body and brain as LEAD. And lead is toxic. So could be that people who have been exposed to more lead were able to absorb less zinc and copper from their bodies. And lead exposure is known to affect intelligence (for the worse). So in some cases, answer could be that dumber people got exposed to more lead.
Also, zinc and copper are relatively easy vitamins to become deficient in, especially in poor quality childhood diets. So could be the "smarter" people have just been better nourished all round.
Lastly, the smart people may benefit from slight genetic advantages that enable them to better metabolise zinc and copper from their diets. Hence more is absorbed from food, more into the blood stream and brain, more into hair.
I can't quickly find a reputable source to back up this claim. Some argue that any such relationship is weak, at best. But I'll assume it's true, for now.
Zinc and copper compete for some of the same chemical receptors in the body and brain as LEAD. And lead is toxic. So could be that people who have been exposed to more lead were able to absorb less zinc and copper from their bodies. And lead exposure is known to affect intelligence (for the worse). So in some cases, answer could be that dumber people got exposed to more lead.
Also, zinc and copper are relatively easy vitamins to become deficient in, especially in poor quality childhood diets. So could be the "smarter" people have just been better nourished all round.
Lastly, the smart people may benefit from slight genetic advantages that enable them to better metabolise zinc and copper from their diets. Hence more is absorbed from food, more into the blood stream and brain, more into hair.
