Key Words: bone h ealth. nutrition. military. training. calcium. vitamin D
Christine Booth PHD & Julia carins
ABSTRACT
The imp01tance of dietary calcium in the prevention of poor bone health and osteoporosis in later life is well recognised and two National Diet Surveys have highlighted the problem of many Australian women eating insufficient calcium. Surveys of ADF trainees revealed 10 % of Army recruits (mostly male) and 20% of female officers-in-training at risk of not meeting their calcium requirements – mostly due to not eating enough dairy foods. Although the eating habits of female
officers-in-training appear to have improved over the last 10 years. many of the women still fall short of meeting their calcium requirements. Further more. female recruits are more at risk of bone-related injury than males. This paper discusses the nutritional determinants of bone health of most relevance to the ADF. describes some current US and Australian military research and makes some recommendations for prevention of poor bone health among ADF personnel.
BACKGROUND
Changed physical training regimes, improved management of sporting activities and gender-related changes to other physical activities (for example marching), are having a positive effect on reducing injuries during training 1• However, two other important areas of preventive action remain to be addressed, namely improved neuromuscular co-ordination (through specific training exercise and psychosocial approaches)2 and improved bone health.
Bone health is becoming an increasingly important public health issue in Australia. Osteoporosis affects about 30 per cent of postmenopausal women, with more than half of these suffering bone fractures 3 It is also becoming more of a problem for men. The prevalence has been predicted to increase in the next generation and the effects of osteopenia (reduced bone mass) are already being seen more in younger people. Current research tells us the best protection against poor bone health is appropriate resistance exercise. a life-long calcium-rich diet and avoidance of smoking and excessive alcohol consumption. This paper discusses the nutritional determinants of bone health of most relevance to the ADF, describes some current US and Australian military research and makes some recommendations for prevention of poor bone health among ADF personnel.
NUTRITIONAL DETERMINANTS OF BONE HEALTH
Calcium is an essential nutrient and is the major cation of bone. Bone is a living tissue. which is continually being broken down and rebuilt. To enable this process. bone has a requirement for not only calcium. but also for an energy supply. and other nutrients including phosphorus. protein. ascorbic acid, copper, fluorine, iron. magnesium. manganese. vitamin D. vitamin K and zinc5.6. Adequate amounts of these nutrients are essential for bone health.
In adequate calcium consumption contributes to several disorders, osteoporosis being the most commonly studied disorder. An effective detetTent against osteoporosis related fractures appears to be the achievement of maximal skeletal mass or peak bone mass by early adulthood7, and it appears t hat a lifetime pattern of adequate calcium intake seems to produce the most benefit.
The skeleton serves as the primary reserve for calcium, and is indirectly affected by dietary calcium intake and the amount of calcium lost from the body as either urine or sweat. Estimates of calcium requirements have only recently included amounts needed to replace calcium losses through sweat. This has lead to an increase in calcium intake recommendations in recent revisions of the FAO/WH08 and US/Canadian recommendations 9 and the draft revisions to t he Australian/New Zealand recommendations 10
The current Australian RDI for calcium for adults are shown in Table 1 . This recommendation accounts for the large calcium reserve in the skeleton and the fact that negative calcium balance may have to continue for many years before bone failure occurs and also incorporates a margin of safety to meet obligatory losses in 90 per cent of the population 11
Table can be viewed in the full article download
To be able to meet the RDI. the National Health and Medical Research Council (NHMRC) gives advice on food groups and lifestyle patterns that will provide nutrients in adequate amounts. Calcium is found predominately in dairy foods. but smaller amounts can be found in bony fish. legumes. certain nuts. fortified soy beverages and breakfast cereals3. To obtain adequate calcium. the NHMRC recommends three serves per day of dairy foods3.
Australian and New Zealand recommendations for calcium requirements are currently being reviewed. Draft recommendations have followed the approach used by the US of setting a recommended dietary intake based on the Estimated Average Requirement (EAR ).
The proposed recommendations for adults are shown in Table 2.
Table can be viewed in the full article download
It is worth noting that the proposed recommendations are substantially higher than the current Australian RDI, therefore estimates of dietary insufficiency made in t he later sections of this rep011 would be even greater if. or when the new recommendations are adopted. Furthermore the new recommendations equate to the need to consume an extra serve of dairy product per day (ie 4 serves per day).
There are a number of nutritional issues other than calcium intake that impact on bone health. Some of these nutrients or food components enhance or impede calcium absorption. or increase calcium losses from the body. Others affect bone health by mechanisms not closely l inked to calcium intake.
One nutrient of great importance for bone health is vitamin D, a promoter of calcium absorption, it enhances absorption during times of need or reduced calcium intake. Vitamin D can be obtained through the diet. or via skin synthesis when exposed to sunlight 6
Adequate protein is essential for bone health as well as for many other aspects of metabolism. High protein intakes have been shown to increase urinary calcium excretion3• but there is controversy surrounding the notion that high protein diets can be detrimental to bone health. It is likely that a diet containing a moderate level of protein (1-1 .5 g per kilogram body weight) is optimal6
Sodium intake has been linked to urinary calcium excretion. and considering the societal trend of low calcium and high sodium intakes 6 there is a potential for high sodium intake to adversely affect bone health. However the evidence is not conclusive that high sodium intakes necessarily adversely affect bone health 12.
Phosphoms is an essential building block of bone. and is therefore required in adequate quantities to ensure healthy bones. However there is concern that too much phosphorus could be harmful to bone. The replacement of milk drinks with carbonated beverages may also contribute, due to lowered calcium and concomitant elevated phosphorus intakes 6
Vitamin K protects against age related bone loss via vitamin K dependent -carboxylation of certain bone proteins, including osteocalcin – the major non collagenous proteins incorporated in bone matrix during bone formation. The ratio of undercaboxylated ostecalcin ( a protein with a low biological activity ) to total osteocalcin is thought to be the most sensitive maker of vitamin K status’and both low dietary vitamin Kh and increases in undercarboxylated osteocalci n 15 have been linked to low BMD in women. Adequate vitamin K status limits urinary calcium excretion. and enhances vitamin D mineralisation and calcium deposition 16
High levels of caffeine in the diet are detrimental to bone health. Caffeine reduces calcium absorption and increases urinary losses. A study found that as coffee intake increased. milk consumption decreased 17, compounding the problem.
Consumption of large amounts of alcohol is also detrimental to bone health. Alcoholism is a risk for bone health due to poor nutrition. malabsorption of nutrients. the potential for liver disease. direct toxicity to osteoblasts and increased risk of falls6 The notion of potential health benefits from moderate alcohol intake is quite popular. and it appears that moderate alcohol intake could be beneficial to bone health 18
MILITARY RESEARCH INTO BONE HEALTH
The importance of dietary calcium in relation to stress fractures in military personnel is unclear. Studies have repo11ed that calcium intake 19 or supplementation 20 was not associated with the risk of developing stress fractures in military recruits. but dietary calcium intake in injured and control groups was relatively high in these studies.
Poor vitamin D nutrition might be an important bone health factor among certain groups of ADF personnel. including those personnel who live in the southern states of Australia and submariners. Total sunlight deprivation for 68 days was reported to result in a large decrease in serum vitamin D among submariners 21. Submariners and other ADF shift-workers may be at fUI1her risk of poor bone health due to altered circadian rhythm and resultant ‘glucocorticoid-induced osteoporosis’22 Also of interest is the role of vitamin D in the promotion of neuro muscular coordination. Poor vitamin D stat us is associated with impaired balance and mu scular strength22. This is important when considering the role of poor neuro-muscular coordination in the high incidence of falls. trips or slips among ADF personnel 2 .
Lower bone density was found to be a factor inpredisposing male 23 and female 24 members of the US Marine Corps to the development of fractures. Al so in the US, female recruits were found to have disproportionately higher numbers of stress fractures than male recruits undergoing similar train i ng regimes25• 26 27. The incidence of stress fractures among female recruits in the UA Army was 4.?%.Quantitative ultrasound (QUS) measurements of the heel was found to identify those women at highest risk of stress fracture. The relative risk (RR) for stress fracture among those women in the lowest quintile for the QUS measure. speed of sound. was 6.7. The subgroup most at risk was those women who smoked and didn’t exercise (RR =14.4)28
Lower bone mineral density has been found among athletes who lose calci um through profuse sweating without a compensatory increased intake of dietary calcium27 This could be an important consideration when considering the calcium requirements and bone health of ADF personnel operating in tropical environments.
The results of two military trials should be available later this year. The first, being conducted by the Creighton University Osteoporosis Centre. ai ms to determine if calcium and vitamin D intervention can reduce stress fracture incidence by at least 50% in female Naval recruits during basic training and to examine t he potential mechanisms for increasing bone adaptation to intense mechanical loading 29• Over three years they aim to enrol 5.200 participants and compare the stress fracture incidence between placebo-treated and calcium/vitamin D treated women. The second. the ADF bone health survey, is being conducted by DSTO Scottsdale under Task ARM 041145. It aims to determine the prevalence of key risk factors. including diet. exercise. bone tum-over, bone mineral density and anthropometry. and to relate these risk factors to injuries. The survey will be completed during 2006 and these data will be used as the basis for the design of strategies for the prevention of bone-related injuries within the ADF.
Dietary calcium intake of ADF trainees over 10 years Dietary intake data has been recorded for Army recruits in 199830 (first survey) and 200331 (second survey) and for female officers-in-training at ADFA in 199332 (first survey) and 200313 (second survey). The gender and age breakdown of the groups surveyed is presented in Table 3 and the mean dietary intakes of calcium and the estimate of risks are presented in Table 4.
TABLE 3.Gender and age breakdown for the dietary intake surveys over 10 years
Table can be viewed in the full article download
TABLE 4. Mean daily dietary calcium intakes for Army recruits and female officers-in-training over a ten-year period
Table can be viewed in the full article download
It appears that the (mostly) male Army recruits and female ofticers-in-training had mean daily calcium intakes similar to their civilian peers as recorded in the 1995 National Nutrition Survey: 1101 mg and 750 mg respectively 3 . In each survey the under consumption of dairy foods was the major contributing dietary factor to poor dietary calcium intake for those individuals at risk of consuming inadequate dietary calcium. For example, in the case of the most recent survey of female officers in-training. all those who consumed less than the recommended amount of calcium had consumed less than the recommended three serves of dairy foods per day.
Because three different dietary intake methods were used in the four surveys, a statistical comparison of these data is inappropriate. Similarly these data can not be directly compared with the Austral ian National Survey data. The apparent increase in calcium consumption by female-officers-in-training the equates to an extra half-serve of dairy food per day. While this may be encouraging. man y female officers-in-training still fall short of current Australian dietary recommendations. Both the national Dietary Surveys 1983 and 1995 and the results detailed here show that low calcium intakes are more likely associated with women than men. This may indicate that women either may be more likely to avoid dairy foods than men or that their food intake is so low that it affects calcium intake. or both 33. The conclusion drawn i n the 1 993 survey, that a pre-occupation with weight control among the female off icers-i n-training results in under consumption. is most likely still valid among the 2003 study cohort 33 .
CONCLUSIONS AND R EC OMMENDATIONS
Current research indicates the best protection against poor bone health is appropriate resistance exercise, a life-long calcium-rich diet and avoidance of smoking and excessive alcohol consumption. Female trainees appear to be at higher risk of poor bone health than their male peers. ADF personnel undergoing training, that involves high levels of physical activity, and may additionally be conducted in hot conditions, have an increased requirement for calcium. Submariners, personnel engaged in prolonged periods of ‘shift’ work, and personnel living for extended periods in cold southern or northern climates may have additional bone health risk factors related to poor vitamin D status and altered diurnal rhythm. Most importantly, young trainees with inappropriate dietary habits may be setting themselves up for a life time of inadequate calcium intake and a much higher risk of osteoporosis in later life. Under consumption of dairy products was the main reason for poor dietary intake of calcium by trainees. The following recommendations are designed to assist in the prevention of poor bone health among ADF personnel.
The need to consume adequate dietary calcium should be promoted as part of a nutrition education program. An holistic approach to nutrition education is needed. Such a program would not only include some formal lecture material for trainees and instructors. but also involve staff and management of the various food providers on Defence sites. In particular, trainees need specific instruction in making appropriate food choices to meet the nutritional demands of arduous activities. Health promotions aimed at reducing the prevalence of smoking and excessive alcohol consumption should also point out the negative impact on bone health and the resultant increased risk of injury. Education at the beginning of a trainee’s military career will help promote good dietary habits over their time in the ADF.
Sufficient and good range of dairy foods should be provided within the mess and should include low-fat varieties. Similarly, dairy products should be included in the ‘hot boxed’ meals provided to trainees outside the mess. Inclusion of low-fat milk drinks in vending machines and at commercial outlets on Defence sites should be encouraged. Trainees should be encouraged to eat three or four serves of low-fat dairy foods each day. Al though calcium is found predominantly in dairy foods, smaller amounts can be found in fish products where the whole bones are consumed, in legumes and certain nuts or in fortified soy beverages or breakfast cereals. It is recommended that tinned salmon also be provided within the mess and other food outlets on Defence sites.
Additional sources of calcium such as supplements should be considered for ADF personnel engaged instrenuous physical activity in hot cl i mates. particularly w here combat ration packs (CRP) are the major source of nutrition and where dairy products are not readily available. Bio availability from non-food sources (e.g. supplements) depends on the dosage and whether t hey are taken with a meal. Efficiency of absorption of calcium from supplements is greatest at doses of -500 mg. Calcium citrate. calcium carbonate and tri calcium phosphate are suitable supplements, which compare well with milk in terms of calcium bio availability w hen consumed with a meal 1 0 There needs to be an ongoing program of monitoring the dietary intake of ADF personnel, w ith a pm1icular focus on the nutrients most likely to have a negative affect on capability, such as the nutritional risk factors for bone health discussed in this report.
ACKNOWLEDGEMENTS
The authors would like to thank staff at DSTO Scottsdale, Canberra Area Medical Unit-Duntroon and the Australian Recruit Training Centre who cheerfully provided assistance with data collection and project administration.
DECLARATION
There was no conflict of interest with respect to the use of the survey data quoted in this review. The review was sponsored by the Defence Health Services Branch and funded by the Department of Defence in accordance with the Defence Science & Technology Organisations (DSTO) research tasking process. The sponsor gave no direction regarding the publication of this review. DSTO management authorised the release of this manuscript for publication.
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