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The Relation between Bone Mineral Density, Insulin-Like Growth Factor I, Lipoprotein (a), Body Composition, and Muscle Strength in Adolescent Males

Sports Medicine Unit (K.T., P.N., R.L.), Department of Orthopaedics, Department of Geriatrics (P.N.), and Department of Clinical Chemistry (G.H.D.), Umeå University, S-901 87 Ume, and National Institute of Working Life (K.T.), S-907 13 Umeå, Sweden

Address all correspondence and requests for reprints to: Kim Thorsen, M.D., Ph.D., Sports Medicine Unit, Department of Orthopaedics, Umeå University, S-901 87 Umeå, Sweden. E-mail: kim.thorsen{at}idrott.umu.se

Osteoporosis is the most common metabolic bone disease. A low peak bone mass is regarded a risk factor for osteoporosis. Heredity, physical activity, and nutrition are regarded important measures for the observed variance in peak bone mass. Lp(a) lipoprotein is a well-known risk factor for atherosclerosis. Serum insulin-like growth factor I (IGF-I) has been found to be increased in males with early cardiovascular disease. In this study, we evaluated the association between bone mass, body constitution, muscle strength, Lp(a), and IGF-I in 47 Caucasian male adolescents (mean age, 16.9 yr). Bone mineral density (BMD) and body composition were measured by dual x-ray absorptiometry, muscle strength of thigh using an isokinetic dynamometer, IGF-I by RIA, and Lp(a) by enzyme-linked immunosorbent assay. IGF-I was only associated with Lp(a) (r = 0.38, P < 0.01). Lp(a) was related to total body (r = 0.40, P < 0.01), skull (r = 0.45, P < 0.01), and femoral neck BMD (r = 0.44, P < 0.01). Lp(a) was also related to fat mass (r = 0.34, P < 0.05) and muscle strength (r = 0.30–0.42, P < 0.05). After multiple regression and principal component (PC) analysis, the so-called PC body size (weight, fat mass, lean body mass, and muscle strength) was the most significant predictor of BMD (ß = 0.28–0.51, P < 0.05–0.01), followed by the so-called PC physical activity (ß = 0.28–0.38, P < 0.05–0.01, weight-bearing locations). However, the PC analysis confirmed that Lp(a) was an independent predictor of total body, skull, and femoral neck BMD (ß = 0.33–0.36, P < 0.01).

The present investigation confirms that BMD, body size, and muscle strength are closely related and that the level of physical activity is a major determinant of BMD. However, the positive relation of Lp(a), a major risk factor for cardiovascular disease, to BMD has not previously been described. The importance of this observation has to be further investigated.

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