6 October 2009
Just in time for Halloween, a study from the British Journal of Psychiatry by Moore, Carter and van Goozen that uses data from the British Cohort Study to estimate the effect of daily candy intake on adult violent behavior.
They find that 10 year olds that ate candy daily were much more likely to be convicted of a violent crime at age 34 than those who did not eat candy daily. They cite this as evidence that childhood diet has an effect on adult behavior. One of their hypothesized mechanisms is that using candy as a reward for children (e.g. for behavior modification) inhibits the child's ability to delay gratification. And there is evidence that children that posses problems with delayed gratification tend to score lower on a host of measures, including the SATs (see also: the marshmallow studies).
The longitudinal data gives them leverage. For instance, the authors are able to control for parenting style at age 5 along with other variables, such as various scales of behavior problems or mental abilities at age 5 (some of these were discarded in the final analysis because of their variable selection rules). These ease my main concern that "problem children" might lead to a certain type of parenting and also indicate a propensity for violent adult behavior. Their controls help to eliminate this possibility (though, I will say that I am not familiar with this literature and they use fairly complicated scales to measure these concepts).
Strangely, at least to me, they do not seem to control for parental income or socio-economic class. I have a few ideas as to why this might matter. First, candy is relatively cheap compared to a good diet, thus poorer families might be forced to choose the cheaper option when feeding their children. Second, financial pressures lead to time pressures, which could force parents to take shortcuts--feeding their children junk food because it is quick or using it to induce behavior because it is easy. Thus, parental income may matter greatly for candy intake and it also may increase propensity to commit violent crimes. I am not certain this is true, but it seems plausible and unmentioned in the paper. Even if the finding is not causal, however, it is still interesting.