Use of vitamins, minerals, and nutritional supplements by participants in a chemoprevention trial.

BACKGROUND

The growing use of vitamins, minerals, and nutritional supplements has the potential to influence the design and interpretation of randomized controlled trials of chemopreventive agents. To the extent that these complementary agents are effective, they could limit the ability of trials to demonstrate an effect of the agents under study.

METHODS

During the course of a colorectal neoplasia chemoprevention trial using aspirin in a group of colorectal carcinoma survivors, the authors obtained information on the use of vitamins, minerals, and supplements at baseline and every 6 months. The information from 622 study participants was categorized and enumerated.

RESULTS

One or more supplements were used at some time by 341 (55%) subjects. Among those who took supplements, 66% took more than 1 and 13% took 5 or more. The mean number of supplements taken was 2.6 (1.7 standard deviation). Vitamins were the most commonly used (49%), followed by minerals (22%), botanicals (13%), and others (5%). Among the vitamins, the most frequently used were multivitamins (38% of subjects), vitamin C (18%), and vitamin E (22%). Calcium (16%) was the most frequent mineral. Among users, there were no differences in supplement use by age or gender.

CONCLUSIONS

Supplement use was common among colorectal carcinoma survivors enrolled in a prevention trial. Investigators should record the information on supplement use so that the possible impact of the supplements on trial endpoints can be evaluated. It may be necessary to increase the size of studies if many of the subjects take potentially effective supplements.