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I think that it can affect some people more than others, and with some people it can be like a drug dependency.
I have a teenage neighbor who has ADHD, and he has an addiction to sugar, to such an extent that he steals money to get as much sweet sugary things as he can, and it is that bad that he has associated mood swings and becomes violent, and even the school has had to get involved to try and curb the 'addiction'.
I don't think that sugar affects everybody in this way, but I do believe that it does affect quite a number of people.