Serum insulin-like growth factor I in healthy older men in relation to physical activity

The serum level of insulin-like growth factor-I (IGF-I) is lower in old men than in young men. It has been theorized that this change may result in part from the lower level of physical activity in the elderly. The objective of the present study was to test this theory.

Cross-sectional study.

Community-dwelling healthy men.

Twenty-nine young men aged 21-29 and 120 older men aged 58-98. A wide range of habitual physical activity was assured in the older men by recruiting them both in senior centers and in fitness centers.

Serum IGF-I level was measured by radioimmunoassay. Physical activity was estimated as the sum of moderate, hard, and very hard activities in leisure and occupation during the previous week as determined by the interviewer-administered Seven Day Physical Activity Recall questionnaire.

IGF-I was significantly higher (363.7 +/- 16 ng/mL, avg +/- SEM) in the young men than in the senior center older men (219.6 +/- 5 ng/mL) or in the fitness center older men (168.3 +/- 11 ng/mL) (P < 0.01). The level of IGF-I in the senior center older men was higher than that in the fitness center older men (P = 0.05). The physical activity of the fitness center older men (128.5 +/- 15 Kcal/kg/wk, avg +/- SE) was statistically similar to that of the young men (101.3 +/- 19 Kcal/kg/wk). The physical activity levels of both of these groups were significantly higher than that of the senior center older men (33.6 +/- 3 Kcal/kg/wk) (P < 0.010). Within none of the three groups was there a significant correlation between IGF-I and physical activity. When the two groups of older men were combined, there was, in fact, an inverse correlation of IGF-I and physical activity (P = 0.001).

The data do not support the hypothesis that lack of physical activity is responsible for the decline in serum IGF-I with advancing age.