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Thymic involution and function may be an important regulator of health in later life. Poor early growth is known to be a factor affecting thymic function early in life, and it is hypothesized to affect thymic function in later life as well. Previous research has shown that vertebral neural canal (VNC) size is a good measure of early growth, and small VNCs in adults have been associated with decreased health and life-span. To date, however, direct association between VNC size, thymic involution, and function have not been made. VNCs were measured using computed tomography in 16 healthy men, aged 45 to 70, from the Normative Aging Study. In addition, serum TSN-cq, a measure of thymic involution and master regulator of a variety of immune functions, cortisol, blood sugar, weight, height, and sitting height were measured. Stepwise multiple regression showed that for the fasting serum samples, the only predictors of TSN-a, were sitting height (R2 = —0.37, p < 0.05) and VNCs (R2 = 0.16, p = 0.056), accounting for 53% of the variance (p < 0.05). After 100 gram glucose challenge test only the VNCs approached significance (R2 = 0.22, p = 0.055). These preliminary data support the hypothesis that early growth disruption may affect thymic involution and function in adulthood.