Antioxidants Can Decrease Chemo Toxicity
Supplementation may help cancer patients adhere to treatment.
Lead investigator Keith Block, MD, co-founder and medical/scientific director of the
He and co-investigator Robert Newman, PhD, professor of cancer medicine at MD Anderson Cancer Center in
Stressing the benefits of better compliance with chemotherapy, he pointed to a recent study of colon cancer patients showing that those who received a full five to seven months of chemotherapy had higher survival rates than those who only received one to four months of treatment, he pointed out. The mortality rates were twice as high among the 30% of patients who dropped out of the chemotherapy treatment early compared with the group that completed the course of treatment.
The investigators looked at 845 studies published between 1966 and December 2006 from six scientific databases. Of these, 30 trials involving 1,964 patients with a variety of cancer types met inclusion criteria. The vast majority of patients had advanced or relapsed disease.
The antioxidants evaluated were glutathione (nine studies), melatonin (six studies), vitamin A (one study), an antioxidant mixture (three studies), N-acetylcysteine (two studies), vitamin D (five studies), selenium (one study), L-carnitine (one study), Co-Q10 (one study) and ellagic acid (one study).
In 18 of the 30 studies, patients who received oral or IV antioxidant supplements experienced significantly lower toxicity than the control groups. Glutathione, melatonin, and vitamin D showed the most consistent and promising effects. Only the vitamin A study found significantly greater toxicity in the antioxidant group compared with controls, although this was not surprising because the toxicity of high-dose vitamin A is well documented.
Several studies found fewer chemotherapy dose reductions, fewer treatment interruptions, and less need to discontinue treatment prematurely among the antioxidant groups.
Of the 19 studies in the review that reported tumor response and/or survival rates, all but one of the antioxidant groups experienced the same or better re-sponse than the control group. No studies reported significantly worse survival in the antioxidant group.
“Each antioxidant had its own benefits,” Dr. Block said. “The glutathione studies demonstrated that the supplement groups were more likely to complete their prescribed number of chemotherapy cycles compared to the controls. The selenium studies showed more patients who were in the antioxidant arm were able to receive optimal chemotherapy dosing.”
Study findings were reported here at the American Society of Clinical Oncology annual meeting.