Thiamin (thiamine), also known as vitamin B1, is essential in regulating appetite, sleep, and memory, along with other tasks. Like other members of the B vitamin family, thiamin seems to play a minor but notable role in prostate health. For example, a Chinese study compared the diets of 102 men who had prostate cancer with those of 102 healthy men and concluded that increased intakes of thiamin and vitamin C reduced the risk of developing prostate cancer. (Du 1997)
A thiamin deficiency has been seen in some cancer patients who have rapidly growing tumors. Although thiamin supplementation has been used to treat cancer patients who have a thiamin deficiency, taking too much of the vitamin may actually stimulate the growth of some malignant tumors, which suggests that taking thiamin supplements should be limited to people who have proven thiamin deficiency. (Boros 1998)
The RDA for thiamin for adults is 1.5 mg. Foods rich in thiamin include beans, lentils, wheat germ, brown rice, fortified cereals, and yeast. Deficiencies are uncommon but can occur among alcoholics.
Boros LG et al. Thiamine supplementation to cancer patients: a double edged sword. Anticancer Res 1998 Jan-Feb; 18(1B): 595-602
Du S et al. [Relationship between dietary nutrients intakes and human prostate cancer.] Wei Sheng Yan Jiu 1997; 26(2):122-25.