Carcinoid cancer patients often have elevated levels of serotonin or its precursor 5-hydroxytryptophan. Normally, serotonin synthesis accounts for a small fraction of tryptophan catabolism, which should be directed along a pathway that allows partial conversion to niacin; hence, increased diversion of tryptophan toward serotonin could cause variable degrees of niacin deficiency in carcinoid patients. Therefore, the prevalence of niacin deficiency among carcinoid patients was investigated by clinical assessment of pellagra and biochemical assessment of whole blood niacin number, a ratio derived from two biologically active forms of niacin (NAD/NADP × 100).
Clinical and biochemical niacin status were assessed in a cohort of newly diagnosed carcinoid patients with carcinoid syndrome (CCS, n = 36), carcinoid patients without carcinoid syndrome (CWCS, n = 32) and noncarcinoid controls (n = 24) recruited at two primary care clinics. Other aspects of serotonin metabolism were measured by analyses of plasma serotonin and tryptophan and urinary excretion of 5-hydroxyindoleacetic acid.
Biochemical niacin deficiency (niacin number < 130) was significantly more common in CCS patients (10 out of 36) compared to controls (p < 0.05, Fisher's exact test), while CWCS patients displayed an incidence that was not significantly elevated (4 out of 32). Only one CCS patient, who was also identified biochemically as niacin deficient, was clinically diagnosed with pellagra.
Biochemical niacin deficiency is more prevalent among newly diagnosed CCS patients than in controls. Manifestation of pellagra is a less sensitive indicator, and dependence on this endpoint could lead to a lack of appropriate nutritional support for this group of patients.
1Laboratory for Skin Cancer Research, CHUL Research Center (CHUQ), Faculty of Medicine, Laval University, Sainte-Foy, Quebec, Canada
2Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
3Tom Baker Cancer Center and Foothills Medical Center, University of Calgary, Calgary, Alberta, Canada
4Carcinoid Cancer Foundation, Inc., White Plains, New York
5Division of Gastroenterology, Mount Sinai School of Medicine, New York, New York
Reprint requests and correspondence: Girish M. Shah, Ph.D., Laboratory for Skin Cancer Research, CHUL Research Center (CHUQ), 2705, Laurier Boulevard, Room S-16, Sainte-Foy, Quebec, Canada.
Received February 7, 2005; accepted June 13, 2005.