Thiamine, which is usually given in excess to many cancer patients,
should be carefully regulated in people undergoing cancer therapy,
new research shows.
The findings reveal a long-overlooked link between thiamine and
tumor-cell growth. The results suggest that too much thiamine may
actually help tumors grow. They also suggest that rational use of
dietary thiamine may help slow tumor growth.
Thiamine supplementation is commonly recommended to cancer patients
to counteract vitamin B1 deficiencies that can occur with
leukemias, gastrointestinal tumors, and other faster-growing
malignancies. Thiamine deficiency is also a side effect of some types
of chemotherapy, making thiamine supplementation essential for many
Total thiamine levels in a patients diet can be 250% to 20,000%
of the normal daily recommended allowance, however. The government
recommends that men consume 1.4 mg and women 1.0 mg of thiamine per
day, amounts that are easily obtained from a typical American diet.
Medical texts recommend 3 mg of thiamine daily for cancer patients, a
dose that needs to be reevaluated in light of this new research.
Excess Thiamine May Contribute to Tumor Proliferation,
Physicians normally do not worry about excess thiamine because the
vitamin is water-soluble, and the body eliminates what it does not
need. This study indicates, however, that excess thiamine may
contribute to tumor-cell proliferation and to the development of
chemotherapy resistance by tumors.
"Cancer patients should be evaluated for their thiamine status,
and supplementation should be administered only to meet the
patients needs," said Laszlo Boros, a research scientist
in the Department of Surgery at Ohio State University. The study by
Boros and an interdisciplinary research team appears in a recent
issue of Anticancer Research.
The link between thiamine and cancer was first discovered by Laszlo
and the research team last year. That study (published in Cancer
Research) revealed that rapidly dividing cancer cells produce ribose,
which forms the backbone of DNA and RNA using a chemical pathway that
is more intensively used by cancer cells than by healthy cells.
Cancer cells appear to produce ribose using the transketolase (TK) pathway.
"The majority--over 70%--of ribose for DNA/RNA synthesis in
tumor cells that have been studied comes from the TK pathway,"
said Boros. "Nobody expected this pathway to be involved in this
process so intensively." The vitamin is a cofactor that is
necessary for the transketolase enzyme to work, said Boros.
"Its a thiamine-dependent reaction."
The discovery led the research team to search the medical literature
for other reports of a link between the TK pathway and cancer. They
found only one: a 1958 paper that first described the pathway in
"This early observation seems to have been overlooked,"
said Boros. "There is no follow-up data in the medical
literature describing this pathway in cancer cells and the role of
thiamine in the tumor-cell proliferation process."
A New Therapeutic Strategy?
Cancer cells favor the TK pathway because it produces ribose
molecules faster than the oxidative pathway--and ribose molecules are
in constant demand by rapidly dividing cancer cells for the
production of new DNAand RNA.
"When it comes to tumor-cell growth, virus infections, and other
conditions that require rapid DNA/RNA synthesis, cells will use the
transketolase pathway." The ideal solution is to provide
thiamine to the patient but deny it to the tumor.
"This could represent a new strategy to control tumor
growth," said W. Scott Melvin, assistant professor of surgery
and senior author of the study. "It might be done in the future
perhaps through a combination of thiamine restriction and the use of
drugs that inhibit the TK pathway." Such drugs are not yet
available for use in humans, however.
"Right now, were trying to lay down guidelines to prevent
oversupplying thiamine, without letting patients slip into thiamine
deficiency," said Boros, "and we want to emphasize the need
to develop TK inhibitors for the treatment of cancer."