The effect of physical activity on human calcium (Ca) metabolism is still not completely understood. Thus, we investigated fractional Ca absorption using 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-matched sedentary control subjects (GL). Weekly hours spent on physical activity, obtained with a questionnaire were 15.0 +/- 6.6 (GH) and 1.0 +/- 1.4 (GL), respectively. Serum testosterone levels were significantly lower in GH compared with GL (P < 0.005). Dietary Ca intake (4-day food record) was twice as high in GH compared with GL men (P < 0.001). GH had significantly higher serum calcitriol levels and Fc(240) values than GL (P < 0.001 and P < 0.01, respectively). In a stepwise multiple regression analysis including serum levels of 25-hydroxyvitamin D, calcitriol, testosterone, and dietary Ca intake, only calcitriol was significantly correlated with Fc(240) (P = 0. 017). Twenty-four hour renal Ca excretion was only slightly higher in GH compared 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 liter between fluid intake and renal fluid excretion (P < 0.001). In summary, we observed a higher fractional Ca absorption rate in physically active young men compared with sedentary controls which is probably mediated by calcitriol. The low testosterone serum levels of the athletes were obviously not a limiting factor in Ca absorption efficiency. An additional Ca retention might, however, only be obtained if absorbed Ca exceeded total obligatory Ca losses.

The objective of this study was to assess the effect of physical activity on bone density at the distal radius in healthy perimenopausal (23) and postmenopausal (60) women. The 83 women, aged 40-62 years, were randomized into two groups. The women participated in an exercise program of 40 minutes of jogging and 20 minutes of gymnastics three times a week for 1 year (group 1, n = 46) or 6 months (group 2, n = 37), respectively. Subjects in group 2 served as controls during the first 6 months. They were introduced to exercise classes after the first 6 months of the study and wore wrist weights (0.8 kg on each arm) during the gymnastics session. None of the women were on hormone replacement therapy (HRT). Results show a decrease in bone mineral density (BMD) during the first 6 months of the study in group 1 (2%, p < 0.01) and group 2, although this was not significant for the latter group (1.2%, n.s., p = 0.045). There was no significant change in osteocalcin serum concentration, fasting urinary calcium excretion, and calcium serum concentration during the first half of the study. After an additional 6 months, it was possible to stop BMD loss in both groups. Osteocalcin serum concentration significantly increased, and calcium serum concentration significantly decreased in groups 1 and 2. Fasting urinary calcium excretion decreased in both groups, although this was significant only in group 2 during the 1-year study. In conclusion, it proved possible to prevent BMD loss at the distal radius by our exercise program in perimenopausal and postmenopausal women. The effects of exercise may be general as well as localized. According to our results, additional localized benefits from a specific strength-development exercise may be seen.

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.

We investigated the effect of wheat bran on biochemical indicators of Ca and bone metabolism in nineteen healthy women, aged 25·5 (se 0·9) years. Subjects received six wheat bran biscuits or six white flour biscuits per day for a period of 4 weeks (crossover). Wheat bran consumption increased fibre intake from 17·7 (se 1·3) to 29·6 (se 1·3) g/d (7 d food record) and enhanced P intake from 1225 (se 59) mg/d to 1663 (se 65) mg/d; P < 0·001. Mean daily Ca intake during wheat bran consumption (1110 (se 82) mg/d) significantly (P = 0·008) exceeded Ca ingestion during the white flour period (955 (se 67) mg/d). Wheat bran increased the number of defecations per week from 7·9 (se 0·8) to 12·2 (se 1·4) (P = 0·0018). Urinary Ca excretion over 24 h significantly (P = 0·021) decreased from 473 (se 53) μmol/mmol creatinine (control period) to 339 (se 37) μmol/mmol creatinine (wheat bran period). Serum 25-hydroxyvitamin D, 2 h fasting urinary Ca/creatinine excretions and 24 h urinary P excretion remained constant. No differences in serum levels of carboxy-terminal propeptide of type I procollagen (biomarker of bone formation) or in 2 h fasting urinary hydroxyproline/creatinine excretions (biomarker of bone resorption) were observed at the end of the two cycles of dietary supplementation. We conclude that a high fibre intake of approximately 30 g/d has no significant adverse effects on bone turnover in subjects with Ca intakes above 1000 mg/d and that the reduction in 24 h urinary Ca excretion is most probably the result of an adaptation process, induced by a decrease in net absorbed Ca.

Polymorphisms at the vitamin D receptor (VDR) gene have been reported to mediate important differences in bone mineral density (BMD) and bone metabolism. In this longitudinal study we examined the relationships between VDR genotypes and bone metabolism, changes in BMD and changes in ultrasound transmission velocity in a population of healthy unrelated German women. The study population comprised 50 physically active women (aged 43.3 to 62.8 years, 14 premenopausal, 36 postmenopausal) with a daily calcium intake of (mean +/- SD) 1045 +/- 338 mg, who had earlier participated in a longitudinal study on the association of physical activity and bone density and bone turnover. Each participant was genotyped for the BsmI polymorphism at the VDR gene locus. Markers of bone turnover (alkaline phosphatase, osteocalcin, procollagen type I C-terminal propeptide, collagen type I C-terminal telopeptide, tartrate-resistant acid phosphatase) were measured at baseline. BMD (determined by peripheral quantitative computed tomography at the distal radius) and ultrasound transmission velocity through bone (at calcaneus, patella and thumb) were analysed at baseline and 15 months later. The genotypic groups did not differ significantly (p > 0.05) in any of the parameters determined at baseline. Neither were there any differences between these groups in the changes of BMD or ultrasound transmission velocity during the study period. Thus, we conclude that in physically active German women with a relatively high calcium intake the impact of VDR genotypic polymorphisms on bone density, bone metabolism and changes in bone density may be of limited importance.