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INTRODUCTION

  1. Top of page
  2. INTRODUCTION
  3. HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT
  4. ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT
  5. ROLE OF DIET IN SKELETAL DEVELOPMENT
  6. QUESTION OF CALCIUM-ACTIVITY INTERACTION
  7. RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT
  8. CONCLUSION
  9. REFERENCES

Can daily physical activities and regularly practiced healthy eating habits, including sufficient amounts of calcium, optimize skeletal growth? Based on the report of Hutterite women by Wosje et al.,(1) in this issue, the answer is a strong affirmative for females. The remarkable skeletal growth of adolescents, as reflected by gains in bone mineral density (BMD) adult-based Z scores, occurs predominantly after menarche, not before, in this religious group.

The gospel that practically all nutritionists hold is that daily consumption by children and adolescents of the appropriate numbers of servings of foods in the major food groups, according to the food pyramid, should yield healthy bones. The present report by Specker's research team(1) adds one additional step: for further skeletal development in late adolescence and early adulthood, regular physical activity appears absolutely essential. The increase in BMD Z scores of the adult Hutterite women with increasing age up to approximately 50 years is most impressive, and the scores testify to the important interactions between two lifestyle variables: (a) healthy eating that includes adequate amounts of calcium and other nutrients from dairy and other foods and (b) regular work-related physical tasks. The calcium-exercise interaction has been difficult to establish in prospective investigations,(2) but cross-sectional studies published almost a decade ago first suggested that this interaction may be important for skeletal growth.(3,4) The current report of cross-sectional data strongly suggests that bone gains result from such an interaction, even though an effect of calcium on BMD cannot be statistically shown.(1)

In terms of general populations of healthy girls (and probably boys as well) in affluent societies around the globe, both the recommended daily eating habits and the practice of regular school physical activities are decaying. These declines will likely contribute to less than optimal development of the skeleton and may place this generation of young females at increased risk of osteoporotic fractures later in their lives. On the other hand, the healthy lifestyle of the Hutterite women may have delayed hip fractures and reduced age-adjusted fracture rates compared with the average woman in the United States, but data to support this contention are not yet available.

HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT

  1. Top of page
  2. INTRODUCTION
  3. HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT
  4. ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT
  5. ROLE OF DIET IN SKELETAL DEVELOPMENT
  6. QUESTION OF CALCIUM-ACTIVITY INTERACTION
  7. RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT
  8. CONCLUSION
  9. REFERENCES

Surprisingly, little information has been published on hereditary contributions to skeletal development, despite the recent flurry of reports surrounding the vitamin D receptor allele. Probably as many as a dozen or so genes contribute to skeletal growth. Because of the historical limits on entry of different groups into this religious sect, the Hutterites may have a more homogeneous gene pool that favorably impacts skeletal development, but this is not yet clear. Black Americans are one population identified with unusually robust skeletal development, that is, with optimal skeletal growth and BMD measurements (BMD values are typically greater at any age beyond 11 years than their white counterparts).(5) Among whites, a rural population of Turkish women in Anatolia stands out as having the “best” bone values and the lowest rates of osteoporotic hip fractures among females.(6) An explanation for the high bone values of the Turkish women may include their fairly high level of daily physical activities, similar to that of the Hutterites.

Over a decade ago, it was suggested that hereditary contributions to bone mass may approximate 50%,(5) but later estimates provide a range between 60% and 80%.(7–9) Unfolding of the genetic control of bone growth and development is progressing, though at a slow pace. In any event, the contribution of environmental factors, that is, diet and exercise, to bone development, as indicated by BMD measurements, has been shown to account for only small percentages in any analysis.

ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT

  1. Top of page
  2. INTRODUCTION
  3. HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT
  4. ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT
  5. ROLE OF DIET IN SKELETAL DEVELOPMENT
  6. QUESTION OF CALCIUM-ACTIVITY INTERACTION
  7. RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT
  8. CONCLUSION
  9. REFERENCES

That physical activity, above all other environmental determinants of bone mass, plays a dominant role in skeletal development is supported by data from a variety of approaches. A sentinel report by Seeman's group in Australia(10) provides data for prepubertal girls that support their contention that physical activity in young girls, before the age of 11 years, may enhance bone development, a benefit that remains until the postmenopausal years.

An important finding among Dutch males and females between 13 and 28 years of age in a 15-year longitudinal study was that weight-bearing physical activity was, along with body weight, a significant positive predictor of bone mass and also, in the authors' conclusions, of peak bone mass.(11) Their analyses could not show that calcium intake contributed significantly to bone mass either in the adolescent period or after adolescence (early 20s and later 20s groups) of either gender. A possible explanation for not finding a calcium effect rests in the observation that all subjects had good intakes of calcium, that is, means for females were between 941 mg/day in the adolescent group to 1204 for women in the late 20s, and means for males ranged from 1100 in adolescents to 1435 for males in the late 20s. An estimated 80% of the calcium came from milk and other dairy products. The significance of these data lies in the major contribution of physical activities during adolescence to bone mass accrual, and the need to continue these activities during early adulthood for maintaining the adolescent gains.

Several other studies also have assessed the benefits of exercise on skeletal development during late childhood or adolescence and, in general, they support the contention that physical activities are robust determinants of BMC and of peak bone mass (J.J.B. Anderson et al., unpublished data, 1999).(12,13)

ROLE OF DIET IN SKELETAL DEVELOPMENT

  1. Top of page
  2. INTRODUCTION
  3. HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT
  4. ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT
  5. ROLE OF DIET IN SKELETAL DEVELOPMENT
  6. QUESTION OF CALCIUM-ACTIVITY INTERACTION
  7. RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT
  8. CONCLUSION
  9. REFERENCES

A good diet, in terms of western standards, includes high-quality protein food sources, that is, typically, from meats and dairy, plus selected servings from the other food groups. The Dutch, Scandinavian, and Swiss nations have the highest intakes of dairy foods, hence, protein, calcium, phosphorus, and several other micronutrients essential for bone growth and development, in addition to sufficient amounts of energy (calories). Protein and energy drive skeletal growth, if other nutrients are adequate (but not necessarily at recommended intake levels). Female adolescents in these countries also are, on average, taller than adolescents of comparable age in the United States. Bonjour's data on Swiss adolescents exemplifies this point.(14,15) By comparison, the late Hutterite adolescents are not so tall. Yet, when the Hutterite adolescents reach age 18 years, they have greater mean BMC and BMD measurements at the regions of interest than the European females. Mean BMD values of adult Hutterites are typically greater than those of all other adolescent populations, except blacks.

Calcium consumption by the Hutterite girls under 18 years was only approximately 900–1000 mg a day from both dairy and nondairy sources, and perhaps 800 mg of calcium or so were ingested daily by the females over age 18 years. These numbers are somewhat less than the Adequate Intake estimates of the Institute of Medicine (IOM).(16) Intakes of other nutrients, though not given in the Hutterite report,(1) are presumed to approximate current nutrient recommendations.

QUESTION OF CALCIUM-ACTIVITY INTERACTION

  1. Top of page
  2. INTRODUCTION
  3. HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT
  4. ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT
  5. ROLE OF DIET IN SKELETAL DEVELOPMENT
  6. QUESTION OF CALCIUM-ACTIVITY INTERACTION
  7. RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT
  8. CONCLUSION
  9. REFERENCES

An interaction between calcium intake and physical activity has been identified in a few studies; most investigations have not found one. The reasons for not finding such an interaction vary, but a common explanation is that most studies include too few subjects. Therefore, meta-analyses would be more likely to find an interaction between these two variables.

However, based on the Hutterite report(1) and other studies, it seems that calcium per se or calcium in conjunction with other nutrients at adequate intake levels is not the major determinant of skeletal measurements achieved by the end of female growth in height, that is, by ages 16–18 years. The physical activity determinant thus becomes quantitatively more significant than calcium, as shown in regression models of the Hutterite report.(1)

Although only limited information is provided on the overall nutritional profile of the Hutterite women, their nutritional intakes are presumed to meet the needs for practically all nutrients at recommended or near-recommended amounts. In addition, this religious sect avoids cigarette smoking and alcoholic beverages, and they probably use prescription and other drugs sparingly, if at all. The females typically have several pregnancies and lactations, which provide opportunities to renew bone tissue, and their bone tissues may be maintained, if not improved, by their daily physical activities. The risk factors for bone health according to the Hutterite lifestyle, in toto, tend to be all positive, and few or none are negative. The only adverse health characteristic cited in the report was being overweight (which actually favors bone maintenance).

RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT

  1. Top of page
  2. INTRODUCTION
  3. HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT
  4. ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT
  5. ROLE OF DIET IN SKELETAL DEVELOPMENT
  6. QUESTION OF CALCIUM-ACTIVITY INTERACTION
  7. RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT
  8. CONCLUSION
  9. REFERENCES

So, what generalizations about this report(1) can be translated into practical recommendations for improving the bone status of females, and increasingly so of males, in affluent societies? Four approaches seem warranted. First, we need to reinstate the rigor of physical education programs and make these programs work effectively both in our schools and outside in diverse community organizations. (Work activities involving some physical labor also would be beneficial, but more difficult to gain acceptance in these societies.) Increased activity also will help counter the high prevalence of overweight children and adolescents in the United States and other technologically advanced nations. Second, we should return to the basics of optimizing intakes of all the essential nutrients, including calcium, by our children and adolescents through healthy food choices on a daily basis. Third, parents should assume a greater role in assuring that their children practice good health habits—especially eating and exercising—and avoid nonhealthy practices, such as excessive television watching and playing of video games. Fourth, adults of all ages need to incorporate or maintain these same healthy behaviors in their daily lives.

CONCLUSION

  1. Top of page
  2. INTRODUCTION
  3. HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT
  4. ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT
  5. ROLE OF DIET IN SKELETAL DEVELOPMENT
  6. QUESTION OF CALCIUM-ACTIVITY INTERACTION
  7. RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT
  8. CONCLUSION
  9. REFERENCES

Observational population studies, prospective trials, and experimental designs using human subjects have provided evidence for the importance of physical activity in skeletal development, in conjunction with adequate dietary calcium. Consuming an adequate amount of calcium appears critical for optimal skeletal growth, but the precise values of the calcium requirements during the life cycle remain somewhat elusive. Therefore, the current calcium intake recommendations, although possibly high, are appropriate when we have less than ideal information on which to base them. However, what is not considered in the IOM recommendations is the potentially important role of physical activity and its potential interaction with calcium, as has been shown for the Hutterite women. This issue needs additional investigation and information before the next review of dietary calcium recommendations.

REFERENCES

  1. Top of page
  2. INTRODUCTION
  3. HEREDITARY CONTRIBUTIONS TO SKELETAL DEVELOPMENT
  4. ROLE OF PHYSICAL ACTIVITY IN SKELETAL DEVELOPMENT
  5. ROLE OF DIET IN SKELETAL DEVELOPMENT
  6. QUESTION OF CALCIUM-ACTIVITY INTERACTION
  7. RECOMMENDATIONS FOR OPTIMIZING SKELETAL DEVELOPMENT
  8. CONCLUSION
  9. REFERENCES
  • 1
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  • 2
    Specker BL 1996 Evidence for an interaction between calcium intake and physical activity on changes in bone mineral density J Bone Miner Res 11:15391544.
  • 3
    Halioua L, Anderson JJB 1989 Lifetime calcium intake and physical activity habits: Independent and combined effects on the radial bone of healthy premenopausal white women. Am J Clin Nutr 49:534541.
  • 4
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  • 5
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  • 6
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  • 7
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  • 8
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  • 9
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  • 10
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  • 11
    Welten DC, Kemper HCG, Post GB, van Mecheln W, Twisk J, Lips P, Teule GJ 1994 Weight-bearing activity during youth is a more important factor for peak bone mass than calcium intake. J Bone Miner Res 9:10891096.
  • 12
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  • 14
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  • 15
    Theintz G, Buchs B, Rizzoli R, Bonjour J-P 1992 Longitudinal monitoring of bone mass acculation in healthy adolescents: Evidence for a marked reduction after 16 years of age at levels of lumbar spine and femoral neck in female subjects. J Clin Endocrinol Metab 75:10601065.
  • 16
    Institute of Medicine 1997 Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. National Academy Press, Washington, DC, U.S.A.