Combined mineral-supplemented diet and exercise increases bone mass and strength after eight weeks and maintains increases after eight weeks detraining in adult mice

Abstract

Exercise has long-lasting benefits to bone mass and structural strength even after cessation. Combining exercise with a calcium- and phosphorus-supplemented diet increases cortical bone mineral content (BMC), area, and yield force more than exercise alone in adult mice. These increases could also be maintained after stopping exercise if the modified diet is maintained. It was hypothesized that combining exercise with a mineral-supplemented diet would lead to greater cortical BMC, area, and yield force immediately after a lengthy exercise program and after an equally long period of non-exercise (detraining) in adult mice. Male, 16-week old C57Bl/6 mice were assigned to 9 weight-matched groups–a baseline group, exercise and non-exercise groups fed a control or mineral-supplemented diet for 8 weeks, exercise + detraining and non-exercise groups fed a control or mineral-supplemented diet for 16 weeks. Exercise + detraining consisted of 8 weeks of exercise followed by 8 weeks without exercise. The daily exercise program consisted of running on a treadmill at 12 m/min, 30 min/day. After 8 weeks, mice fed the supplemented diet had greater tibial cortical BMC and area, trabecular bone volume/tissue volume (BV/TV), bone mineral density (vBMD), yield force, and ultimate force than mice fed the control diet. Exercise increased cortical BMC and area only when coupled with the supplemented diet. After 16 weeks, both exercised and non-exercised mice fed the supplemented diet maintained greater tibial cortical BMC and area, trabecular BV/TV, vBMD, yield force, and ultimate force than mice fed the control diet. Combining exercise with a mineral-supplemented diet leads to greater bone mass and structural strength than exercise alone. These benefits remain after an equally long period of detraining. Long-term use of dietary mineral supplements may help increase and maintain bone mass with aging in adult mice.

Calcium and phosphorus supplemented diet increases bone volume after thirty days of high speed treadmill exercise in adult mice

“…2 , 3 and 4 ). The diet and exercise regimen in this study (4 weeks, 20 min exercise per day) resulted in similar effects on tibial bone mass and strength as previous studies that involved longer durations of exercise (8 weeks, 30 min exercise per day) 2 , 5 . Direct tibial loading in rodents has diminished effectiveness when applied for a large number of load cycles per day, but the number of loading cycles used here was an order of magnitude greater 26 .…”

“…Diet formulations were the same as we have used previously 2 , 5 . The control diet was an AIN-93G diet (TestDiet®, Richmond, IN) that was modified by adding dicalcium phosphate to contain 0.5% Ca and 0.5% P. In the supplemented diet, dicalcium phosphate and calcium carbonate were added to give the diet 5% Ca and 1% P. Dietary mineral amounts and Ca:P ratio were all designed to increase serum Ca by increasing passive absorption of Ca in the intestines 2 , 5 , 35 – 37 . For the control diet, the food had 3.90 kcal/g, and the calorie distribution was 65.0% carbohydrates, 16.3% fat, and 18.7% protein, while the supplemented diet had 3.39 kcal/g with the same calorie distribution.…”

“…Cortical and trabecular bone micro-CT measurements were obtained as we have detailed 5 . Whole tibiae were embedded in agarose, and scanned using a micro-CT specimen scanner (µCT100 Scanco Medical, Bassersdorf, Switzerland).…”

“…Weight-bearing exercise in humans and mice can increase bone mass, structural (whole bone)-level strength, and/or tissue quality, making bone better able to resist fracture 1 – 4 . Exercise can also have long-term benefits to bone health even after detraining 5 – 13 . In humans, bone mass peaks at ~ 25 years of age and declines thereafter.…”

Changes in Muscle Mass and Composition by Exercise and Hypoxia as Assessed by DEXA in Mice

“…However, for mice, and likely other small rodents, the manual designation lacks specificity, thus we manually designated tissue types. The whole mouse was designated as soft tissue, based on the assumption that four weeks was not a long enough time to elicit changes in bone density [ 21 , 22 ]. The remainder of the scan area including the tail was designated as the material air.…”