Evidence for an acute rise of intestinal calcium absorption in response to aerobic exercise.

Background: The acute effects of physical activity on intestinal calcium (Ca) uptake and on bone metabolism are not known.

Aim Of The Study: To investigate the consequences of an acute aerobic exercise bout on fractional Ca absorption and on biomarkers of bone turnover.

Methods: With the use of a cross over design, eighteen male athletes, aged 25.2 (SE 0.6) years, either had to perform a 60 min run (70 % of maximal speed) or had to rest for 60 min. Intestinal Ca absorption (Fc(240)) was assessed by the use of a stable strontium test. Moreover, calciotropic hormones and serum C-Telopeptide (CTx), a biomarker of bone collagen degradation, and serum C-terminal propeptide of type I collagen (PICP), a marker of bone collagen formation, were measured prior (t(-60)) and 3 hours after (t(240)) exercise or rest.

Results: Fc(240) values were significantly enhanced in response to exercise compared to rest (16.2 +/- 0.7 % vs. 14.6 +/- 0.8 %; P < 0.05). PICP values were significantly lower in response to exercise compared to rest: -9.8 % (P < 0.05). Exercise did not influence serum levels of intact parathyroid hormone and calcitriol. Serum CTx levels decreased markedly between t(-60) and t(240) during both intervention periods (both P values < 0.001), the results being in line with the circadian rhythm of serum CTx.

Conclusions: A moderate exercise bout can induce an acute rise in fractional Ca absorption. Moreover, even in endurance-trained young men a moderate exercise bout acutely decreases bone collagen formation, while the physiologic fluctuations of the bone resorption marker CTx remain unaffected.