This randomised trial will investigate the effect of calcium supplementation on bone and calcium metabolism in women during acute load carriage exercise. This study will test the hypothesis that calcium supplementation before load carriage exercise will attenuate the decline in serum ionised calcium and increase in parathyroid hormone and bone resorption.
Endurance exercise decreases serum ionised calcium and increases parathyroid hormone and bone resorption. These disturbances to calcium homeostasis can be attenuated by calcium supplementation before exercise. Military field exercises are characterised by high exercising energy expenditures, restricted dietary intake, and prolonged periods of load carriage. These exercise and nutritional challenges can result in impaired bone turnover, a negative calcium balance, and an increased risk of stress fracture. It is unknown if military load carriage disturbs calcium homeostasis and whether calcium supplementation before exercise can attenuate this disturbance. This crossover randomised controlled trial will investigate the effect of acute calcium supplementation on bone and calcium metabolism in women during acute load carriage exercise. Each participant will complete two 2 h load carriage trials. The trials will be performed after either consuming 1000 mg of calcium one hour before or with no treatment. During each experimental trial blood and urine will be sampled for markers of bone and calcium metabolism. Primary Outcome: The absolute change in urine calcium balance (Ca44:Ca42) between pre- and post-load carriage will be compared between the non-supplemented (Control) and calcium supplemented trial (Supplement) using one-way ANCOVAs with pre-load carriage calcium balance (either as a ratio, or both the numerator and denominator) as the covariate, or a linear mixed model with the restricted maximum likelihood estimation to allow incorporation of incomplete data. Secondary Outcomes: Circulating measures of bone turnover and calcium metabolism during load carriage will be compared between Control and Supplement using linear mixed models with the restricted maximum likelihood estimation to allow incorporation of incomplete data.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
PREVENTION
Masking
NONE
Enrollment
40
Daily calcium food supplement.
Army Health and Performance Laboratory
Camberley, Surry, United Kingdom
RECRUITINGChange in calcium balance.
The ratio of the calcium isotopes Ca44:Ca42 in spot urine samples.
Time frame: Before and immediately after exercise.
Circulating calcium isotopes during load carriage.
The ratio of the calcium isotopes Ca44 and Ca42 (Ca44:Ca42) in blood.
Time frame: Before and immediately after exercise.
Bone turnover during load carriage.
Circulating concentration of procollagen type 1 N-terminal propeptide (P1NP), beta carboxy-terminal cross-linking telopeptide of type 1 collagen (βCTX), osteocalcin, and sclerostin.
Time frame: 0, 20, 40, 60, 80, 100, and 120 minutes during, and 15, 30, 60 and 90 minutes following, exercise.
Calcium metabolism during load carriage.
Circulating concentration of ionized calcium, phosphate, and intact parathyroid hormone.
Time frame: 0, 20, 40, 60, 80, 100, and 120 minutes during, and 15, 30, 60 and 90 minutes following, exercise.
Dermal calcium loss.
Concentrations of total calcium and the ratio of the calcium isotopes Ca44 and Ca42 (Ca44:Ca42) in sweat.
Time frame: During exercise.
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