Exercise-trained young men have higher calcium absorption rates and plasmacalcitriol levels compared with age-matched sedentary controls

The effect of physical activity on human calcium (Ca) metabolism is still n ot completely understood. Thus, we investigated fractional Ca absorption us ing a stable strontium test (Fc(240)), calciotropic hormones, and renal Ca excretion in 31 young men with a high activity level (GH) and in 26 age-mat ched sedentary control subjects (GL). Weekly hours spent on physical activi ty, obtained with a questionnaire were 15.0 +/- 6.6 (GH) and 1.0 +/- 1.4 (G L), respectively, Serum testosterone levels were significantly lower in GH compared with GL (P < 0.005). Dietary Ca intake (4-day food record) was twi ce as high in GH compared with GL men (P < 0.001). GH had significantly hig her serum calcitriol levels and Fc(240) values than GL (P < 0.001 and P < 0 .01, respectively). In a stepwise multiple regression analysis including se rum levels of 25-hydroxy-vitamin D, calcitriol, testosterone, and dietary C a intake, only calcitriol was significantly correlated with Fc(240) (P 0.01 7). Twenty-four hour renal Ca excretion was only slightly higher in GH comp ared with GL (P < 0.05). However, additional Ca losses might have occurred through the extensive sweating of GH, as indicated by a difference of 1.7 l iter between fluid intake and renal fluid excretion (P < 0.001). In summary , we observed a higher fractional Ca absorption rate in physically active y oung men compared with sedentary controls which is probably mediated by cal citriol. The low testosterone serum levels of the athletes were obviously n ot a limiting factor in Ca absorption efficiency. An additional Ca retentio n might, however, only be obtained if absorbed Ca exceeded total obligatory Ca losses.