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

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

To investigate the consequences of an acute aerobic exercise bout on fractional Ca absorption and on biomarkers of bone turnover.

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.

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.

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.