VITAMIN-D DEFICIENCY IN VETERANS WITH CHRONIC SPINAL-CORD INJURY

Chronic spinal cord injury (SCI) is associated with osteopenia, increa sing the prevalence of long-bone fractures. Although disuse may be the primary cause of osteopenia, identification of any additional mechani sms of bone loss may lead to potential therapeutic interventions. We i nvestigated the relationships of serum calcium (Ca), phosphorus (PO4), albumin, alkaline phosphatase (Alk P), and parathyroid hormone (PTH) with serum 25-hydroxyvitamin D [1,25(OH)D] in 100 subjects with chroni c SCI and 50 control subjects. In a subgroup of 50 subjects with SCI a nd 50 control subjects, we correlated these parameters with serum 1,25 -dihydroxyvitamin D [1,25(OH)(2)D]. Mean ages for the group with SCI a nd the controls were the same. In subjects with SCI, the duration of i njury was 20 +/- 1 years (mean +/- SD). Thirty-two of 100 subjects wit h SCI, as compared with eight of 50 controls, had serum 25(OH)D levels less than the normal range (chi(2) = 4.36, P <.05). In subjects with SCI, a negative correlation was demonstrated between serum 25(OH)D and PTH (r =.29, P <.005). Mean serum 1,25(OH)(2)D levels were significan tly elevated in subjects with SCI as compared with controls (61 +/- 21 v 46 +/- 18 pg/mL, P <.0005). Twenty of 50 subjects with SCI had seru m 1,25(OH)(2)D levels greater than 62 pg/mL, as compared with 10 of 50 controls (chi(2) = 4.76, P <.05). A positive correlation was found be tween serum PTH and 1,25(OH)(2)D in subjects with SCI and controls (r =.41, P <.005 and r =.30, P <.05, respectively). Twelve subjects with SCI had serum PTH levels greater than the normal range. In this high-s erum PTH subgroup, serum 25(OH)D concentration was significantly lower (P <.05) and serum 1,25(OH)(2)D and Alk P concentrations were signifi cantly higher (P <.005 and P <.05, respectively) as compared with the subgroup with serum PTH values within the normal range. In subjects wi th SCI, 17 had a serum Ca concentration less than 8.5 mg/dL. In person s with SCI, depressed levels of serum 25(OH)D, as well as other factor s, may result in forces inclined to reduce the serum calcium concentra tion. A state of mild secondary hyperparathyroidism may result, thus i ncreasing the conversion of serum 25(OH)D to 1,25(OH)(2)D. These data suggest that in chronic SCI subjects, as in the general population, se cretion of PTH and the increase of circulating 1,25(OH)(2)D are subjec t to control by negative-feedback mechanisms. Higher levels of serum P TH would be expected to accelerate bone resorption of a skeleton alrea dy regionally osteoporotic as a consequence of the bone mineral loss d ue to acute immobilization. Copyright (C) 1995 hy W.B. Saunders Compan y