Handbook of Vitamin C Research

136Chin-San LiuA study conducted in Japan reported that lymphocyte vitamin C level was significantlylower in type 2 diabetic patients, although a similar reduction in vitamin C levels was notobserved in plasma [130]. Plasma vitamin C concentration reflects the transient utilization ofdigestive foods such as fruit, supplements, and vegetables. It has been reported thatlymphocytes maintain a vitamin C concentration as large as 80- to 100-fold across the plasmamembrane and that they have cell-membrane transporting mechanisms between vitamin Cand glucose.. Lymphocytes participate in many immune responses, and high levels ofantioxidant activity have been reported in these cells [131]. In diabetes, therefore, themeasurement of lymphocyte vitamin C might be a more reliable antioxidant biomarker thanplasma vitamin C level. Similar results have been found in type 1 diabetes [132]. Plasmaascorbic acid status depends on the interactions of dietary vitamin C intake, plasma insulin,and glucose concentrations. Insulin can promote the uptake of vitamin C, but hyperglycemiawill inhibit renal vitamin C re-absorption. In type 1 DM, an adequate dietary vitamin C intakeis often associated with an unexpectedly low ascorbic acid status in lymphocytes. Vitamin Cmay play a role as an aldose reductase inhibitor. In addition, water-soluble antioxidants, suchas ascorbic acid, in body fluids are potentially very important as adjuncts to tighten glycemiccontrol in the management of diabetes.In the European Prospective Investigation of Cancer–Norfolk study, Harding et al.administered a semi-quantitative food frequency questionnaire to a population of 21,831healthy individuals aged 40 to 75 years [133]. Plasma vitamin C concentration wasdetermined and habitual intake of fruit and vegetables was assessed. At the end of the 12-yearfollow-up study, diabetes was incidentally diagnosed in 3.4% (n=735) of that population.Their results revealed an inverse correlation between plasma vitamin C levels and the risk ofdeveloping diabetes. They proposed that the mechanisms might be related to the high fibercontent in fruit and vegetables, which may reduce obesity, or possibly to the antioxidativecapacity of vitamin C, which may protect against the development of diabetes.Scurvy and Oral HealthScurvy occurs because of reduced intake or malabsorption of vitamin C. At-risk groupsinclude the poor (because of reduced access to groceries), food faddists, widowers, andindividuals with purported allergies to multiple fruit and vegetable products. Other at-riskgroups include persons with gastrointestinal disease (e.g. colitis), anatomical abnormalities,or poor dentition. Cancer patients on chemotherapy who have increased nausea and diarrheaare also at risk, as are patients on hemodialysis. Psychiatric disorders (e.g. depression,schizophrenia, or anorexia) have also been recognized as putting patients at risk for reducedintake of vitamin C. Alcoholic persons represent one of the largest groups at risk for scurvybecause they may have poorly balanced diets and because alcohol decreases the absorption ofvitamin C [134]. Patients with scurvy exhibit various systemic manifestations. Severeconstitutional symptoms (e.g. weakness, fatigue, or myalgia) may be secondary to anemia,which develops in 75% of patients because of blood loss, concomitant folate deficiency, oraltered iron absorption [7, 135]. Anemia is most commonly normochromic normocytic [7].Myalgia occurs because of the reduced production of carnitine [135]. Scurvy causes changes