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."