Objective: Delayed sexual maturation and low body weight is common in cystic fibrosis (CF). Concomitant data on sex hormones and concomitant body composition are lacking in men with CF. Design: Cross-sectional study. Subjects and methods: Serum levels of testosterone, 17b-oestradiol (E 2 ), 25-hydroxyvitamin D (25(OH)D), sex hormone-binding globulin (SHBG) and LH were measured by RIA and total and regional lean body mass (LBM), fat body mass (FBM), bone mineral content and bone mineral density (BMD) were assessed by dual-energy X-ray absorptiometry, in men with CF (n ¼ 40; age 24:7^5:4 years) and age-matched healthy controls ðn ¼ 28; age 25:7^3:7Þ: Only men without acute disease exacerbation or systemic glucocorticoid treatment were included. Results: Mean levels of hormonal serum parameters differed significantly between healthy controls ðtestosterone ¼ 20:2^5:5 nmol=l; E 2 ¼ 95:0^20:2 pmol=l; 25ðOHÞD ¼ 62:8^28:3 nmol=lÞ and patients ðtestosterone ¼ 15:9^4:1 nmol=l; E 2 ¼ 60:7^19:4 pmol=l; 25ðOHÞD ¼ 39:5^17:8 nmol=l; P , 0:001Þ while no difference was found for SHBG or LH. Eleven (for E 2 , 19 of 40, for 25(OH)D, 20 of 40) out of 40 patients had serum testosterone levels 2 S.D. below the mean of normal. Men with CF showed a relative shift from FBM to LBM and a different body fat distribution compared with healthy controls ðP , 0:01Þ: Testosterone was not correlated with weight, total or regional LBM or FBM, but significantly with BMD ðr ¼ 0:32; P , 0:05Þ independently from body height and 25(OH)D levels. E 2 was correlated with regional and total FBM ðr ¼ 0:48; P , 0:05Þ: In a multiple regression analysis of the joint effect of testosterone and body components on E 2 , a testosteroneindependent effect was found for FBM. Conclusions: CF patients with stable disease have moderately reduced serum testosterone levels. This might already imply detrimental effects on bone. The change in LBM of patients appears to have no direct association with sex hormone levels while low FBM might cause reduced net conversion of serum testosterone to E 2 with possible effects on FBM distribution.

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