Nutritional Determinants of Bone Health: Implications for the Australian Defence Force

In   Issue .

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.

 

 

Acknowledgements

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