Are there any correlations of ibs to nervous system disorders like alzheimer's and parkinson's? what about correlations with ethnic background? if so, what is the hypothesis as to why these corrltns?

Alzheimer's : Older african-americans are 2x as likely to get ad, while hispanics have 1 1/12 x the risk of the general population. There are no known associations between ibs and ad.

I am not: Awarenot aware of any correlation to irritable bowel and dementia or parkinson's disease. It is often related to anxiety, which, in it's most severe forms can be related to dementia but irritible bowel and it's associated anxiety are pretty easy to control.

Vascular and social: Ethnic correlations with respect to dementia are probably related to differences among ethnicities in the prevalence of vascular risk factors such as hypertension (which is more common in african americans). Also, certain ethnicities have disadvantages related to socioeconomic status and access to care. Genetics also play a role and especially how genes interact with the environment.