This seminar was conducted in New Zealand and the summary prepared for circulation to Nutrition Australia members.

Measuring Up: A Symposium on Calcium’s Contribution to Bone Health

Inadequate calcium intakes are a significant problem worldwide and this can have a major impact on bone health.  The link between calcium intake, bone health and osteoporosis was the focus of a one-day symposium held in Auckland on 29 October 2001.

Speakers included Ms Donnell Alexander from NEW ZEALAND MILK, Professor Connie Weaver from Purdue University in Indiana in the USA, Dr Nigel Gilchrist from Princess Margaret Hospital in Christchurch, Professor Edith Lau from the Chinese University of Hong Kong and Dr Hilary Green from Massey University, Palmerston North.  The Chair of the symposium was Professor Ian Reid, Head of the Department of Medicine at the University of Auckland.

NEW ZEALAND MILK sponsored the symposium; a summary of the presentations is given below.

Key Nutritional Issues in Bone Health
Ms Donnell Alexander

Background information was presented on osteoporosis, followed by a broad overview of the key nutritional issues in bone health.

In the USA, the National Osteoporosis Foundation has estimated that one in two women and one in eight men over the age of 50, living in industrialised areas, will suffer a fracture as a result of osteoporosis.  Hip fractures in particular are associated with a high level of morbidity and mortality: 25% of hip fractures result in death within one year, 50% result in long-term hospital stays and only 25% fully recover. Osteoporosis results in a great economic, social and personal burden.  Global projections on hip fracture highlight some worrying trends (see Figure 1).

Figure 1: Global Projections for Hip Fracture (adapted from Cooper & Melton, 1996)

There are a number of risk factors for osteoporosis; some are modifiable, as shown in Table 1.

Table 1: Risk Factors for Osteoporosis

The key nutrients that have an impact on bone health are as follows:

·        Calcium is an essential nutrient for bone rigidity and strength; 99% of the calcium in the body is contained within the bones.

·        Phosphorous is important for bone structure.

·        Magnesium is important for bone strength.

·        Zinc is a co-factor in bone mineralisation.

·        Copper may have a role in bone composition and structure, but more research is needed in this area.

·        Iron is a co-factor in collagen synthesis.

·        Boron may play a role in bone health, but more research is needed in this area.

·        Vitamin D is very important for bones, helping to facilitate calcium metabolism.

·        Vitamin A is required by osteoblasts and osteoclasts.

·        Vitamin B6 is needed for bone strength in animals, but there are no studies in humans to date.

·        Vitamin C is needed for collagen cross-linking and may reduce the risk of osteoporosis in smokers owing to its antioxidant function.

·        Vitamin K is an integral part of osteocalcin and matrix-GLA protein.

·        Protein is a fundamental component of bone, needed for synthesis of collagen fibres.

Other factors that have an impact on bone health include:

·        caffeine, which can increase the loss of calcium from the body; however this is only thought to be important in those who are deficient in calcium

·        alcohol, which can increase the relative risk of fracture if intakes reach in excess of 25g per day on a regular basis.  Moderate intakes, however, may have a beneficial effect on bone mineral density

·        phyto oestrogens, which may have an effect on bone mineral density, but most studies to date have been on animals; more research is needed on humans.

In summary, osteoporosis is a serious health concern and diet is a critical modifiable risk factor.  Calcium and vitamin D are key nutrients which play a role in bone health; many other nutrients are, however, also important.  Dairy products are an excellent source of protein, calcium and vitamin D and also contain magnesium, zinc and vitamin A, all of which are important for bone health.  A balanced and varied diet, combined with regular moderate weight-bearing physical activity, should be promoted.

Calcium – How Much is Enough? An International Perspective

Professor Connie Weaver

Professor Weaver highlighted the fact that calcium is a vitally important nutrient for all ages:

• during the growing years to maximise peak bone mass
• during adult life to maintain bone mass
• during older adulthood to reduce bone loss.

Most studies have shown that in children there is an increase in bone mineral density when the diet is supplemented with calcium, either as supplements or as dairy foods.

Professor Weaver went on to discuss the different approaches to determining optimal calcium intakes.  Methods that can be used include:

1. Maximum Retention
2. Factorial Method
3. Current Population Intakes.

1. Maximum Retention

As calcium intakes increase, calcium retention increases.  This occurs up to a certain level, after which there is a plateau effect and any extra intakes are excreted.  The level at which a plateau occurs is the maximum retention level and is the level of optimal intake.  This is shown in Figure 2.

Camp Calcium

Professor Weaver went on to present data from her Camp Calcium studies.  The first study presented involved a 21-day intervention trial on girls aged 12 to 14 years.  The girls were studied twice at a lower and higher calcium intake in a crossover design during the same summer; calcium intakes ranged from 600mg to 2300mg per day.  Results showed the maximum retention of calcium occurred at a level of 1300mg per day and this became the recommended intake in the USA for this age group. 

Professor Weaver estimated that if adolescent girls increased their intake of calcium from 918mg to 1300mg per day, this could increase skeletal mass by up to 4% per year. 

It is thought that extra calcium in the diet leads to a reduction in bone resorption (bone loss) and that this is the protective mechanism involved.

Although the calcium requirement in the teenage girls studied was 1300mg per day, there are a number of factors that could alter requirements, including the bioavailability of the calcium in the diet, the amount of salt and protein consumed, the level of exercise, hormonal status, genetics and race.  The girls in the study were consuming a diet high in salt and protein; if the diet were lower in salt and protein calcium requirements may be less. 

A second study at Camp Calcium looked at the effects of race and salt intake on calcium retention.  This was a randomised crossover study of black and Caucasian girls given 800mg per day of calcium and either a high-salt (3.86g per day) or low-salt (1.3g per day) diet.  There were racial differences in the level of salt excreted on a high-salt diet, with black girls retaining more salt and calcium than white girls.  Both race and diet were found to have an effect on calcium retention. 

A further study, presented by Professor Weaver, looked at the effects of both exercise and oral contraceptive use on bone mineral density in women aged 18 to 30.  Oral contraceptive use had a negative impact on bone mineral content, especially in individuals who exercised.  This loss was offset if they consumed an adequate level of calcium. 

Further information is needed on maximal retention of calcium, in particular for:

• male youths
• adults at peak bone mass
• post-menopausal women
• non-white populations.

2. Factorial Method

The factorial approach to calculating calcium requirements looks at total requirements, and then factors in a percentage absorption figure.  British recommended dietary intakes for calcium are based on this approach.

By way of an example, for adolescent girls, the factorial approach can be used to calculate requirements as shown in Figure 3.

Figure 3: The Factorial Approach for Determining Calcium Requirements in Adolescent Girls

3. Current Population Intakes

Population intakes of calcium vary widely, and as osteoporosis becomes an increasing problem this data is less likely to be used to determine requirements for calcium.

Current recommended intakes for calcium are shown in Table 2.

Table 2: Current Calcium Recommendations in Different Countries

Low calcium intakes tend to be associated with hip fracture risk. Table 3 shows calcium intakes and the risk of hip fracture in those aged 50 to 65 and in those aged over 65.

Table 3: Hip Fracture Risk and Calcium Intakes

Professor Weaver went on to discuss the tendency of young girls to diet.  In fact a recent WHO survey (www.ruhbc.ed.ac./uk/hbsc) found that 10% of girls were dieting by the age of 11 years, and 25% were dieting by the age of 15 years.  Only half of the dieters were drinking milk at least once a day. 

In conclusion, further clinical research on calcium could increase our understanding of calcium requirements by gender, age and race.  Also, more research is needed into how calcium requirements are altered by diet, exercise and hormonal factors.  It is particularly important to encourage young people to consume adequate calcium to ensure optimal bone health throughout life.

The Importance of Milk for Growing Children and Adolescents: Clinical Research Results

Dr Nigel Gilchrist

Dr Gilchrist presented the results of a study of children aged 8 to 10 years, the aims of which were to:

• look at the effect of a calcium-enriched flavoured product on bone density, bone growth, bone size, height and weight
• determine the acceptability of the product in children of this age.

This was a randomised placebo-controlled trial where 154 children were given either a placebo containing 400mg calcium per day or a calcium-enriched product containing 1200mg per day.  Measurements were taken for height and weight at baseline and again at 6, 12 and 18 months, as well as 12 months after the cessation of the study.  Pubertal development was assessed with a self-administered questionnaire and a medical questionnaire was administered at baseline and at follow-up. 

Both the treatment group and the control group had a high baseline intake of calcium, around 1000mg per day, and baseline intakes remained constant throughout the study.  There were no differences in anthropometrical measurements in the treatment group and the control group. 

There were a significant number of dropouts at the start of the study, around 50%.  The main reason for this was a dislike of the taste of the milk. 

No difference was seen between the groups in measurements for bone growth and bone size.  This might have been because of the high baseline intakes.

Dr Gilchrist went on to present data from a second study, which looked at the effect of consuming dairy products over a two-year period in 15-year-old girls (Merrilees et al 2000).  The aims of the study were to:

• examine the effects and benefits of a high-calcium intake from dairy products on bone mineral density, body composition, lipids and biochemistry
• determine whether a high intake of dairy products is acceptable in this age group.

One hundred and five girls aged 15 to 16 years participated in the two-year randomised controlled study.  The girls were randomly allocated to either a control group (who continued to follow their normal diet) or a dairy supplemented group (who were provided with supplemental dairy products providing 1000mg calcium per day).  Ninety-one girls completed the two-year study and were followed up for a further year after the cessation of dairy supplementation. 

There were no differences in the anthropometrical measurements of the two groups and there was no significant change in lipid profiles throughout the study.  Baseline intake of calcium was 750mg per day; the supplemented group was consuming 1200mg per day, along with a higher intake of protein and phosphorous.  At the end of the one-year follow-up period, the girls who had been in the supplemented group had returned to their original dairy intakes.  There were no significant differences in exercise levels, in preference for or acceptability of dairy products, or in lipids and bone markers between baseline, the end of supplementation and one-year follow up. 

There was a significant increase in bone mineral density in the supplemented group at the end of the two-year supplementation period, in the trochanter (4.6%), lumbar spine (1.5%) and femoral neck (4.8%).  When the girls left the controlled environment and returned to baseline intakes of calcium, the beneficial effect was lost.

Dr Gilchrist concluded by saying that in young children there was no additional benefit in bone density and bone size with supplemental calcium, but there was a benefit in adolescent girls.  This may have been because there was a high baseline intake of calcium in the younger children; this was not the case in the adolescents.  There were no adverse effects of calcium supplementation on total body fat, body weight or cholesterol levels.  Further research is needed on calcium intakes and requirements in children.  It is particularly important to ensure adequate calcium intakes in adolescent girls.

The Effect of Milk Supplementation on the Rate of Bone Accretion in Chinese Children in Hong Kong

Professor Edith Lau

Calcium intakes in Asia are very low, on average about 500mg per day.  Activity levels are also low, especially in children who have heavy schoolwork loads.  These factors together increase the risk of osteoporosis later in life.

Professor Lau presented a randomised controlled trial that looked at the effect of milk supplementation on the rate of bone accretion in Chinese children aged 9 to 10 years in Hong Kong.  A total of 324 subjects were recruited: a control group with 122 subjects was given no intervention; one treatment group of 100 subjects was given 40g of high calcium milk (ANDEC) per day, providing 650mg calcium; and a second treatment group was given 80g of high-calcium milk (ANDEC) per day, providing 1300mg calcium.  Randomisation was based on school classes rather than individuals for ease of administration.  Measurements were taken every six months up to 30 months for bone mineral content, bone mineral density, height, weight, tanner staging, three-day food record and activity questionnaire.

At baseline there were no significant differences between the groups in terms of energy, protein, fat and calcium intakes.  Calcium intakes were 400mg to 500mg per day at baseline.  There was also no statistical difference in bone mineral density at baseline, so all the groups were comparable.

Compliance throughout the study was excellent.  Results were analysed using ANCOVA by repeated measures and were adjusted by tanner staging, baseline age, weight, height and bone mineral density.

Results showed that in boys, the supplemented groups had a higher bone mineral density at all sites when compared with the non-supplemented group.  The supplemented groups were also taller, but the difference in height was not significant. 

Amongst the girls, the supplemented groups also had a higher bone mineral density than the control group.  Although directions of the differences in the boys and girls were very similar, the difference between the girls was not statistically significant.  There were no height differences in the girls, although the supplemented groups did gain more weight. 

Overall, the results show more bone gain amongst those being supplemented with high-calcium milk.  The differences were statistically significant in the boys, but were not significant in the girls. 

Milk supplementation may enhance bone accretion in Chinese children, but longer-term results will give more information on the effect of calcium on changes in bone mineral density over time.  It is planned to extend this study for a further 12 months, so the results will be assessed again at 30 months. 

Biochemical Bone Markers: Clinical and Research Applications for Biochemical Markers of Bone Turnover

Dr Hilary Green

Dr Green presented information on the place of bone markers both in clinical practice and in research.  She stated that bone markers were not useful for the diagnosis of osteoporosis in individuals, but were useful for monitoring responses to pharmaceutical or nutritional interventions in groups of people.

Markers of bone formation include bone alkaline phosphatase, osteocalcin and procollagen terminal peptides.  Markers of bone resorption include pyridinoline, deoxypiridinoline, N-telopeptides and C-telopeptides.

Dr Green went on to present a research study she had conducted on a group of women who consumed two glasses of high-calcium milk over a four-week period, providing 1200mg calcium per day.  In this study, consumption of milk resulted in a significant reduction in bone resorption in as little as two weeks in a group of post-menopausal women.  There was no change in bone formation, even after four weeks.  A longer period of study may be necessary to see a change in bone formation.

In summary, biochemical bone markers are useful tools for:

• tracking individual responses to therapy
• assessing whether an intervention is likely to have a long-term effect on bone mineral density
• predicting fracture risk.

The Effects of Milk Supplementation on Bone Density in Post-Menopausal Women

Professor Edith Lau

Osteoporosis is likely to become a significant public health problem in Asia over the next few years.  It has been estimated that by 2050 3.2 million hip fractures will occur  per year in Asia, accounting for half the hip fractures in the world.  Over the past 30 years in Hong Kong there has been a significant increase in the number of hip fractures.  The reasons for this are unknown, but may be related to anthropometrical changes and changes in physical activity.

There are a number of factors that increase the risk of osteoporosis. Professor Lau presented data from the Asian Osteoporosis Study on relative risk (RR) for hip fracture.  This is shown in Table 4.

Table 4: RR for Risk Factors for Hip Fracture

Calcium intakes in Asia are relatively low; dairy products provide only 23% of the calcium in the diet, the rest is provided by vegetables and soy, grains, and fish with bones.

Professor Lau went on to present the results of a three-year randomised clinical controlled trial on post-menopausal women.  The study involved 200 women who were randomised into two groups.  The women in the intervention group had their diets supplemented with high-calcium milk (milk has extra nutrients apart from just calcium that are beneficial for bones, such as protein and vitamin D, so is preferable to calcium supplements).  The control group received no intervention and the study group received two sachets of high-calcium milk powder (ANLENE) each day providing 800mg of supplementary calcium.  Follow-up was every six months over a three-year period.  Subjects were six to seven years post-menopause, at baseline calcium intake was around 450mg to 500mg per day and the groups were comparable in terms of height and weight.  Compliance was very good, with an average of 93%.

Results showed that there was a loss of 0.25% bone mineral density at the spine in the milk group and a loss of 2% bone mineral density at the spine in the control group.  The difference was highly statistically significant at all sites.  Similar trends were seen at the hip, femoral neck and total body.  There was a significantly smaller difference in the late post-menopausal woman, compared with the early post-menopausal women.

Professor Lau concluded that milk consumption was a sustainable and acceptable intervention over a three-year period.  Consumption of milk was effective in reducing the rate of bone loss in post-menopausal Chinese women.  This study has important public health implications; if milk intake is increased in the population this may help to prevent the predicted epidemic of osteoporosis in Asia.

References

Cooper C and Melton LJ, Magnitude and impact of osteoporosis and fractures,
In R Marcus, D Ledman and J Kelsey (eds), Osteoporosis, San Diego, CA,
Academic Press. 1996.

Lau EMC, Woo J, Lam V and Hong A,  Milk supplementation of the diet of postmenopausal Chinese women on a low calcium intake retards bone loss, Journal of Bone and Mineral Research 2001; 16(9):1704-1709.

Merrilees MJ, Smart EJ, Gilchrist NL et al, Effects of dairy food supplements on bone mineral density in teenage girls, European Journal of Nutrition 2000; 39(6):256-262.

Speaker biographies

Professor Ian R Reid, BSc, MBChB, MD, FRACP, FRSNZ

Ian Reid is Professor and Head of the Department of Medicine at the University of Auckland, New Zealand.  He received his under-graduate medical degrees there and subsequently trained as an endocrinologist and completed an MD.  He held a post-doctoral fellowship at Washington University, St Louis, from 1985 to 1987 when he returned to the University of Auckland.

His group is closely involved in the development of bisphosphonates for use in osteoporosis; in documenting the effects of calcium supplementation on bone density; and in studies of the mechanisms and management of steroid osteoporosis, post-menopausal osteoporosis, Paget’s disease and primary hyperparathyroidism.

Professor Reid is Secretary/Treasurer of the International Bone and Mineral Society, and Secretary of the Asian Pacific Osteoporosis Foundation. He was formerly President of the Australia and New Zealand Bone and Mineral Society.  Professor Reid is a Fellow of the Royal Society of New Zealand.

Ms Donnell Alexander, MSc, Dip Diet, RD

Donnell Alexander is a Nutrition Research Manager in Bone Health for NEW ZEALAND MILK in Wellington, New Zealand.  A Registered Dietician, she holds an MSc in Human Nutrition and a Post-Graduate Diploma in Dietetics from the University of Otago in Dunedin, New Zealand.

Ms Alexander has worked as a nutritionist at NEW ZEALAND MILK for over three years, supporting its product development and marketing initiatives.  She has a particular interest in the nutritional requirements of older adults and young children and has contributed to the development of specialised milk products targeted at meeting their needs.

Her career includes extensive experience in the public health research sector in both New Zealand and the United Kingdom.  Ms Alexander has worked on national nutrition survey programmes both in New Zealand and in the UK and was involved in the latest COMA Committee Report on Nutrition and Bone Health in the UK. 

She is an active member of the New Zealand Dietetics Association, the New Zealand Nutrition Society, the New Zealand Guild of Food Writers, the American Oil Chemists Society and the New Zealand Nutrition Foundation.

Professor Connie M Weaver, MSc, PhD

Connie Weaver is Distinguished Professor and Head of the Department of Foods and Nutrition at Purdue University, Indiana, USA.  In 2000, she also became Director of a National Institute of Health-funded Botanical Center to study dietary supplements containing polyphenolics for age-related diseases.  Her research interests include mineral bioavailability, calcium metabolism and bone health.

Dr Weaver received a Bachelor of Science and Master of Science in Food Science and Human Nutrition from Oregon State University.  She received a PhD in Food Science and Human Nutrition from Florida State University and holds minors in Chemistry and Plant Physiology.

She was a member of the US National Academy of Sciences Food and Nutrition Board Panel that developed new recommendations for requirements for calcium and related minerals.  Dr Weaver is past-President of the American Society for Nutritional Sciences and is on the Board of Trustees of the International Life Sciences Institute.  For her contributions to teaching, Dr Weaver was awarded Purdue University’s Outstanding Teaching Award.  In 1993, she was honoured with the Purdue University Health Promotion Award for Women and, in 1997, she received the Institute of Food Technologists’ Babcock Hart Award.

Dr Nigel Gilchrist

Based in Christchurch, New Zealand, Nigel Gilchrist is a Specialist Consultant Physician with particular interest in programmes for the prevention, diagnosis and treatment of osteoporosis.  Dr Gilchrist is also interested in medical and post-operative surgical problems in the elderly and works with the Leinster Orthopaedic Centre in Christchurch.  He is the Principal Trustee for the Canterbury Geriatric Medical Research Trust. 

Dr Gilchrist is a Senior Clinical Lecturer in Medicine for the University of Otago, Christchurch Clinical School.

Professor Edith Ming-Chu Lau, FHKAM, FFPHM, FRCP (Edin), MD, MSc, MBBS

Edith Lau is Associate Professor, Department of Community and Family Medicine at the Chinese University of Hong Kong (CUHK).  Professor Lau specialises in osteoporosis research, focusing on epidemiology, genetics and clinical trials.  Together with Professor PC Leung of CUHK, she was awarded a grant of $40 million from the Hong Kong Jockey Club Charity Trust to set up an osteoporosis centre.

Professor Lau originally documented the following findings: that an epidemic of osteoporosis was occurring in the 1980s in Hong Kong; that a low dietary calcium intake and lack of load-bearing activity contributed 20% to the risk of hip fracture in Hong Kong; and that the oestrogen receptor gene was related to bone mass in Chinese women.  Professor Lau was the Principal Investigator of the Asian Osteoporosis Study, which is the first and only multi-centre study on osteoporosis conducted in Asia.

She is President of both the Asian Pacific Osteoporosis Foundation and the Hong Kong Osteoporosis Foundation.  Professor Lau was a member of the year 2000 WHO Task Force on Osteoporosis and is a member of the WHO Task Force for the Bone and Joint Decade.

Dr Hilary Green, PhD

Hilary Green is Senior Research Scientist at the Milk and Health Research Centre, which is part of the Institute of Food, Nutrition and Human Health at Massey University, in Palmerston North, New Zealand. Before taking up her current position in 1998, she was a Teaching Fellow in Clinical Nutrition in the Department of Medicine at St James’s University Hospital, Leeds, England.

Dr Green’s research background is in applied human physiology.  She has a PhD in Human Physiology from the University of Nottingham Medical School’s Department of Physiology and Pharmacology.

Her current research focuses on the impact of cow’s milk on human health and nutrition, with a particular interest in bone health.