Committee on Military Nutrition Research: Activity Report 1994-1999 (1999)

As part of the Defense Women's Health Research Program, the U.S. Army Medical Research and Materiel Command requested that the Subcommittee on Body Composition, Nutrition, and Health of Military Women (BCNH subcommittee) in addition to their evaluation of the effect of current military fitness and body composition standards on the nutrition and health of military women, also identify and provide recommendations regarding special nutritional considerations of active-duty military women. An area identified for further study in military women concerned the effect of calcium, as well as total energy intake, on the incidence of stress fractures in the short term, and osteoporosis in the long term and the nutrient implications of these conditions.

The incidence of stress fractures during U.S. military basic training is significantly higher in female recruits than in male recruits (IOM, 1992a; 1998a). This injury has a marked impact on the health of service personnel and imposes a significant financial burden on the military by delaying the training of new recruits. Strew fractures increase the length of training time, program costs, and time to military readiness. In addition, stress fractures, a short-term risk, may share their etiology with the long-term risk of osteoporosis.

In order to address these issues adequately in the short timetable of the proposal, the BCNH, a subcommittee of the Committee on Military Nutrition Research (CMNR), held a workshop December 7–9, 1997. The workshop included experts in the areas of endocrinology, calcium metabolism, bone mineral assessment, sports medicine, and military nutrition to evaluate the effects of diet, genetics, and physical activity on bone mineral and calcium status in young servicewomen. Specifically, the subcommittee (and thus, the speakers) were asked to consider the effects of dietary restriction at the levels observed in military women, combined with the physical demands of basic training, both on short-term bone mineral status (and the

immediate risk of stress fracture) and on the long-term risk of osteoporosis. In so doing, the subcommittee was asked to respond to the following five questions:

1. Why is the incidence of stress fractures in military basic training greater for women than for men?
2. What is the relationship of genetics and body composition to bone density and the incidence of stress fractures in women?
3. What are the effects of diet, physical activity, contraceptive use, and other lifestyle factors (smoking and alcohol) on the accrual of peak bone mineral content, incidence of stress fractures, and development of osteoporosis in military women?
4. How do caloric restriction and disordered eating patterns affect hormonal balance and the accrual and maintenance of peak bone mineral content?
5. How can the military best ensure that the dietary intakes of active-duty military women in training and throughout their military careers do not contribute to an increased incidence of stress fractures and osteoporosis?

In considering the questions posed by the military (and as a follow-on activity to the subcommittee's earlier report, Assessing Readiness in Military Women [IOM, 1998]), the subcommittee consulted with a liaison panel comprising military researchers and health care personnel. The BCNH subcommittee met in executive session following the workshop to begin drafting their brief report. The subcommittee met in executive session for an additional writing session and to discuss their conclusions and recommendations on January 27, 1998. Based on information gathered from discussion with the workshop speakers, the military liaison panel and a brief review of the literature on bone metabolism and risk factors for bone health, the subcommittee prepared this brief report, Reducing Stress Fractures in Physically Active Military Women . The report was submitted to the sponsor in June, 1998.

Low initial fitness of recruits appears to be the principal factor in the development of stress fractures during basic training. The basic training period may be insufficient time to achieve the aerobic fitness level required and the musculoskeletal adaptations necessary to avoid injury.

Muscle mass, strength, and resistance to fatigue with cyclic loading (bone stress created by rapid or excessive incremental skeletal muscle contraction and loading forces) play a critical role in the development of stress fracture. The etiology of stress fracture is multifactorial, and bone mineral density is only one contributing factor. Genetics and body mass, specifically muscle mass, are also important determinants of stress fracture.

Energy intake by military women should be adequate to maintain weight during training. Nutritional modification of diets of incoming recruits cannot effectively prevent stress fractures during the short term of basic training. The use of oral contraceptives is not contraindicated. Exogenous estrogen-progestagen hormones may positively affect peak bone mass reached in adulthood whereas any conditions that induce estrogen deficiency (e.g. training regimen, diet, weight loss) may adversely affect the skeleton. It is likely that maintenance of appropriate body weight is important in preventing the onset of secondary amenorrhea.

The subcommittee's key recommendations and recommendations for future research are summarized as follows:

Training and Physical Fitness Assessment

• Develop a more appropriate fitness standard for women through a structured program prior to basic training or through an integrated program with basic training. This program should be designed to increase the level of activity gradually.
• Focus the basic training program on alternating low impact loading and higher impact routines that lead to cardiopulmonary fitness to avoid training errors.
• Emphasize a program of continual physical fitness; this will assist in the maintenance of weight, fat-free mass, and bone mass in all servicemembers.
• Perform fitness and body composition assessments more frequently, and in a manner that will foster adherence to healthy weight and physical fitness practices.
• Use of bone mineral measurements for routine screening of recruits to determine stress fracture susceptibility is not recommended at this time.
• Develop a research effort to compile data from all military services on initial fitness level of recruits by age, gender, and race/ethnicity
• Develop a research effort to collect stress fracture incidence statistics by age, gender, race/ethnicity, and skeletal site, using a gender-independent, standardized definition and collect data during a comparable time frame from all military services during both the basic training and post-training periods.
• As recommended previously (AFEB, 1996), develop research to determine the types of activities that may predispose women to stress fractures, especially in the pelvic region and upper leg. Develop modifications of these activities in basic training to lower risk.

Nutrition and Related Factors

• Ensure that energy intakes by military women are consistent and adequate to maintain weight during intense physical fitness training.
• Aim aggressive education programs at helping military women identify and select appropriate foods and fortified food products to meet their nutrient requirements.
• Continue to gather dietary intake data and evidence concerning calcium intakes throughout a soldiers' career as training programs, food choices and food supply change over time.
• Develop research efforts to assist in identifying those factors, such as diet, lifestyle, and ethnicity, that may contribute to achieving peak bone mass, as well as components of military programs that may interfere with this process.
• Develop research to assess the effect of military women's dietary energy status on the secretion of hormones that affect bone health, particularly in situations of high stress. Little is known about the prevalence and underlying causes of menstrual cycle disturbances (oligomenorrhea, amenorrhea).
• Evidence indicates that oral contraceptives have no detrimental effects on bone mineral density, and may in fact have a positive effect. Develop a research program to determine the effects of implant and injectable contraceptives on bone mineral density and bone health.

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The committee's responses to the questions, conclusions, and recommendations from this report are included in Appendix J.