Disorders of carbohydrate and lipid metabolism in veterans with paraplegia or quadriplegia: A model of premature aging

Abstract

One hundred veterans with paralysis due to spinal cord injury (SCI), equally divided between those with paraplegia and quadriplegia, and 50 able-bodied veteran controls underwent a 75-g oral glucose tolerance test (OGTT). In subjects with SCI, 22% were diabetic by criteria established by the World Health Organization (WHO), whereas only 6% of the control group were diabetic. Eighty-two percent of the controls had normal (NL) oral glucose tolerance, compared with 38% of those with quadriplegia and 50% of those with paraplegia. Subjects with diabetes mellitus (DM) were older in both the SCI and control groups, but those with SCI developed carbohydrate disorders at younger ages than did the control group. SCI subjects had significantly higher mean glucose and insulin values at several points during the OGTT when compared with controls, suggesting an accentuated state of insulin resistance in those with SCI. Mean fasting plasma glucose (FPG) values for both SCI and control groups were significantly higher in subjects with DM compared with those with NL glucose tolerance. When the FPG value was compared between SCI or control subjects with abnormalities in glucose tolerance, the subgroups with SCI and NL or impaired glucose tolerance (IGT) had significantly lower FPG levels than the respective control subgroups, suggestive of decreased hepatic glucose output in SCI. The mean insulin response to an oral glucose challenge was significantly higher for SCI (90 to 180 minutes) or control (90 and 120 minutes) subjects with IGT compared with their respective subgroups with NL glucose tolerance; in the subgroups with DM, the insulin response was significantly greater in subjects with SCI (120 and 180 minutes) and controls (120 minutes) compared with those with NL glucose tolerance. Determinations of insulin sensitivity (S i), percent lean (%L), percent fat (%F), and cardiopulmonary fitness (V̇ O 2 max) were performed. Values of S i by the minimal model method were linearly correlated with those of V̇ O 2 max determined from a progressive incremental upper-body exercise stress test. Values of S i were not significantly correlated with those of %L or %F by dual-energy X-ray absorptiometry (DEXA). Thus, in untrained subjects with SCI, the strongest determinant of S i was cardiopulmonary fitness, rather than body adiposity as in able-bodied individuals. Serum lipid levels in subjects with SCI showed a decreased high-density lipoprotein (HDL) cholesterol level (38 ± 1 mg/dL), a direct correlation between peak plasma insulin and serum triglyceride (TG), and a strong inverse correlation between serum TG and HDL cholesterol. In conclusion, SCI predisposes to carbohydrate and lipid abnormalities, largely as a consequence of extreme inactivity, and this constellation of metabolic findings appears to occur prematurely.