Serum Insulin-Like Growth Factor I Levels in Adult Diabetic Patients: The Effect ofAge

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Abstract
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 n i 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 < 0.001). I n both groups there was a marked decline in IGF-I with increasing age (P < 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 i n age-matched normal subjects, but did notdiffer between the two diabetic groups. Glycosylated hemoglobin levels correlated inversely with IGF-I levels only in younger patients with IDDM (r = −0.486; P < 0.05 for patients aged 21−40 yr). We conclude that factors common to IDDM and NIDDM, perhaps related torelative nutritional deficiency at the cellular level, cause a reduction in serum IGF-I levels, and thatthis reduction occurs independently of age-related changes in IGF-I. (J ClinEndocri-nol Metab63: 651, i986)