Serum insulin-like growth factor I levels in adult diabetic patients: the effect of age.

Despite reports of reduced serum insulin-like growth factor (IGF) levels in experimentally diabetic animals, human diabetic patients have been reported to have decreased, normal, or even elevated levels. This study was a cross-sectional examination of the effect of age on immunoreactive IGF-I levels in adult patients with insulin-dependent or noninsulin-dependent diabetes mellitus (IDDM and NIDDM) attending a diabetes out-patient clinic. The patients and normal subjects studied were divided into the age ranges 21-30, 31-40, 41-50, 51-60, and over 60 yr. For all ages combined, the mean IGF-I level (+/- SD) was 0.84 +/- 0.26 U/ml (202 +/- 62 ng/ml) in 133 normal subjects, significantly reduced to 0.41 +/- 0.17 U/ml in 121 IDDM patients, and 0.49 +/- 0.19 U/ml in 46 NIDDM patients (both P less than 0.001). In both groups there was a marked decline in IGF-I with increasing age (P less than 0.01). Except for NIDDM patients aged 21-30 yr (only two patients), IGF-I levels in both IDDM and NIDDM patients were significantly lower in every age range than those in age-matched normal subjects, but did not differ between the two diabetic groups. Glycosylated hemoglobin levels correlated inversely with IGF-I levels only in younger patients with IDDM (r = -0.486; P less than 0.05 for patients aged 21-40 yr). We conclude that factors common to IDDM and NIDDM, perhaps related to relative nutritional deficiency at the cellular level, cause a reduction in serum IGF-I levels, and that this reduction occurs independently of age-related changes in IGF-I.