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 kinds of chemotherapy. Severe thiamine deficiencies can lead to nervous system and memory impairment, and the build-up of lactic acid in the blood.
Thiamine supplementation is therefore often essential for cancer patients.
However, total thiamine levels in a patient's diet can be 250 to 20,000 percent of the normal daily recommended allowance. 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 re-evaluated in light of this new research. Physicians normally don't worry about excess thiamine because the vitamin is water-soluble, and the body eliminates what it doesn't need. This study indicates, however, that excess thiamine may contribute to tumor-cell proliferation and to the development of chemotherapy resistance by tumors.