Abstract
Nutritional factors affecting bone health throughout the lifecycle has received considerable attention in the literature but little is known about the influence of nutrition on stress fracture (SF) risk. Royal Marine (RM) recruits undergo a 32-week arduous military training programme, where the prevalence of SF has been -5% over recent years. The Institute of Naval Medicine was tasked by Surgeon General to investigate risk factors associated with stress fracture during RM training at the Commando Training Centre Royal Marines. The present thesis focuses on the nutritional aspects of this work, with the primary aim to identify the influence of past and present dietary intake and nutritional status on SF risk and bone health in RM recruits.A bespoke dietary assessment tool was developed to investigate nutritional intake relative to SF risk and training success in a cohort of RM recruits (n=545). No aspects of diet during training were associated with SF risk. However, recruits with a higher energy intake during training were more likely to successfully complete training (P<0. 05). Poor aerobic fitness, low body mass (less than 65 kg) and small thigh girth were independent risk factors for SF (n=27; P<0. 05). In a larger cohort of RM recruits (n=1090), childhood (0-12 y), adolescent (12-18 y) and pre-RM training diets were assessed with a food frequency questionnaire. Vitamin D and micronutrient status were assessed in serum blood samples. Childhood milk intake and adolescent fruit and vegetable intakes were associated with bone quality (assessed by Broadband Ultrasound Attenuation) (P<0. 05). Low milk intake during childhood, and high intake of fizzy drinks during adolescence, were associated with increased SF risk (n=75; P<0. 05). Importantly, serum 25(OH)D (as a marker of vitamin D status) <60 nmol. L-1 was associated with increased SF risk (P<0. 05). Stress fractured recruits (n=65) and matched controls (n=65) underwent Dual Energy X-ray Absorptiometry and peripheral Quantitative Computed Tomography scanning. Stress fractured recruits had lower bone density of the lumbar spine and hip, and narrower tibiae than their matched controls. These novel data suggest an important role for lifestyle factors in the pathogenesis of SF in a military population, with concomitant bone density/structure differences at key fracture sites. Further research (including a possible vitamin D supplementation intervention) is warranted.