The patient was a 76-year-old man referred to our clinic with screening results suspicious for gastric cancer. His past medical history consisted of hypertension and benign prostatic hypertrophy. Physical examination and laboratory data were nonspecific except for asymptomatic macroamylasemia. Esophagogastroduodenoscopy showed a 20 mm type 0-IIc lesion in the gastric subcardia, preoperatively diagnosed as cT1, cN0, cM0, cP0, cStage IA. The patient underwent a planned total gastrectomy with D1 lymphadenectomy followed by Roux-en-Y reconstruction with no complications. The postoperative course was unremarkable, and the patient was discharged on postoperative day 10. Pathologic evaluation revealed an 8 mm moderately differentiated tubular adenocarcinoma on the anterior wall. Macroscopically, the tumor was flat and slightly depressed (type 0-IIc). Histologically, it showed an INFbeta growth pattern, and the tumor invaded the submucosa (pT1 SM). There was no evidence of lymph node (pN0) or liver (pH0) metastasis or venous (v0) or lymphatic (ly0) invasion. The proximal and distal resection margins were clear. Peritoneal cytology was also negative (pP0, CY0). The final stage was pT1N0M0, Stage IA according to the Japanese classification of gastric carcinoma staging system).
Except for occasional heartburn, a sense of abdominal distension, and elevated serum amylase levels, he had no obvious signs and symptoms during postoperative follow-up. He took nifedipine (Adalat CR , Bayer Healthcare, Osaka, Japan), theophylline (Theodur , Mitsubishi Tanabe Pharma, Tokyo, Japan), etizolam (Depas , Mitsubishi Tanabe Pharma), bifidobacterium (Lac-B Granular Powder , Kowa Company Ltd., Nagoya, Japan), magnesium hydrate (Yoshida Pharmaceutical, Tokyo, Japan) and eviprostat (Eviprostat , Nippon Shinyaku, Kyoto, Japan). His basal serum vitamin B12 level was followed monthly and initially maintained within the normal range by intramuscular injections of mecobalamin (Methycobal , Eisai, Tokyo, Japan). Nine months after surgery, his serum vitamin B12 levels suddenly increased to 33,000 pg/ml, which is approximately 36-fold higher than the normal range (233-914 pg/ml). This level of hypercobalaminemia persisted for approximately one year without mecobalamin injections. The patient's diet did not contain any obvious excess sources of vitamin B12. Fortunately, he did not show any obvious symptoms or laboratory abnormalities (Table 1). He later reported that he had started drinking half a bottle of an energy drink as a supplement during this time. After he discontinued the energy drink, his serum vitamin B12 levels quickly declined to within the normal range (Figure 1). The ingredients on the energy drink label included caffeine, fructose, beta-carotene, vitamins B2, B6 and C, octacosanol, garlic, licorice, ginseng, bracket fungus, Polygonatum falcatum and chlorella extract; there was no mention of vitamin B12. Concentration analysis revealed an undetectable amount of vitamin B12 in the energy drink.