Beta carotene levels and mortality risk:
Intake of vegetables containing beta carotene was associated with a lower risk for all causes of death including cancer but no benefit was seen with taking beta-carotene supplements. Greenberg ER et al tested beta carotene levels in subjects prior to being randomized to take beta carotene supplements. Subjects with an intial beta carotene level of 0.34 to 0.52 umol/L had a 51% less risk of dying from cancer when compared to subjects with the lowest intial beta carotene levels of under 0.21 umol/L. Those subjects with an intitial beta carotene level of over 0.52 umol/L had a lower risk of death from all causes. There was no reduced risk of disease or mortality benefit in subjects who took beta carotene supplements in pill form. (7)