There are at least 20 studies in the literature. The most recent
paper by O'Leary DH et al, NEJM 1999;340:14-22 was a prospective study
with a sample size of 5858 subjects and a  median follow-up of 6.2
years. It will be most helpful. If you need any other information on
this subject you can contact me.

Nicos Labropoulos
Assistant Professor of Surgery
Dept. of Surgery
Loyola Univ Med Ctr
2160 S. 1st Ave
Maywood, IL 60153
tel: 708 327-2898
fax: 708 327-2698