Broccoli, cabbage and a variant gene
A class of nutrients, isothiocyanates, found only in cruciferous vegetables - broccoli, cauliflower, cabbage, watercress, bok choy, among others - was protective against lung cancer in the study of a sample of 18,244 males, 45-64 years old, in Shanghai, China. The study also showed a unique gene-diet interaction. Subjects genetically deficient in an enzyme (GSTM1) that quickly eliminates isothiocyanates (ITCs) from the body got the most benefit from cruciferous vegetables, presumably because ITCs stayed around longer to confer their protective effect.
Among all subjects, those with detectable levels of isothiocyanates in the urine had a 40% decrease risk of lung cancer. Among those lacking the metabolism enzyme, a 64% decrease was noted.
Precursors of ITCs, a class of naturally occurring chemicals, are released when cruciferous vegetables are chewed and the anticarcinogenic isothiocyanates are formed.
The study appearing in the journal Lancet (Vol. 355) was a collaboration by scientists at the National Institute of Environmental Health Sciences, Research Triangle Park, N.C.; University of Southern California, Los Angeles; American Health Foundation, Valhalla, N.Y.; and Shanghai Cancer Institute, China. The study was funded through grants by NIEHS and the National Cancer Institute, agencies of the National Institutes of Health.
Both blood and urine samples were collected from study participants. The urine test for total ITC levels was developed by the researchers specifically for epidemiological research. Stephanie London, NIEHS, a co-lead-author, said, "We are aware of no prior data linking a biologic marker of ITC intake to the risk of any cancer." The authors noted that the benefits of ITCs may vary between individuals and across populations based on genetic variation in metabolism.
Subjects in the study were followed up through annual contacts with all surviving cohort members and a twice yearly review of cancer reports from the Shanghai Cancer registry and of death certificates.
"The main take home message is not that veggies are good," London said. " It is that we demonstrated a gene-diet interaction. The beneficial effect of ITCs was predominantly seen among subjects who are predicted to metabolize it more slowly based on their having deletion of a gene (GSTM1) that rapidly eliminates these compounds from the body. The implication for intervention studies is important. There is a lot of animal work on ITCs which includes work to figure out which of them you would want to use in an intervention and in what form. Our study adds significant human data to this effort."
NIEHS PR # 00-11
Journal
The Lancet