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High Calcium Intake No Better for Bone Health - full text pdf below
 
 
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"With ageing populations, the burden of osteoporotic fractures on society will increase in the coming years1 and the prevention of osteoporotic fractures is therefore a major public health issue. The importance and optimal level of calcium intake to compensate for skeletal calcium losses and for the prevention of osteoporosis and fractures have been much debated and remain unclear. This is reflected by the wide range of daily calcium recommendations for individuals older than 50 years: at present 700 mg in the UK,2 800 mg in Scandinavia, 1200 mg in the United States, and 1300 mg in Australia and New Zealand...... Against this background, we aimed to investigate associations between long term dietary intake of calcium with risk of fracture of any type, with hip fractures, and with osteoporosis, in a large, population based prospective study of Swedish women......there was a tendency towards a higher hip fracture rate within the lowest quintile of dietary calcium intake in combination with a low dietary vitamin D intake.....Incremental increases in calcium intake above the level corresponding to the first quintile of our female population were not associated with a further reduction of osteoporotic fracture rate."
 
Principal findings

 
These findings show an association between a low habitual dietary calcium intake (lowest quintile) and an increased risk of fractures and of osteoporosis. Above this base level, we observed only minor differences in risk. The rate of hip fracture was even increased in those with high dietary calcium intakes.
 
What is already known on this topic
· Meta-analyses of randomised trials have found that supplemental calcium does not reduce the risk of fracture in community dwelling women
 
· Meta-analyses of previous cohort studies have not established a reduction in fracture or osteoporosis risk with increasing calcium intake
 
· Dietary nutrient estimates are imprecise, and large studies are therefore needed to detect thresholds in risk of fracture and osteoporosis What this study adds
 
· Dietary calcium intakes below approximately 700 mg per day in women were associated with an increased risk of hip fracture, any fracture, and of osteoporosis
 
· The highest reported calcium intake did not further reduce the risk of fractures of any type, or of osteoporosis, but was associated with a higher rate of hip fracture
 
High Calcium Intake No Better for Bone Health - full text pdf below
 
By Michael Smith, North American Correspondent, MedPage Today
Published: May 24, 2011
 
"There's plenty of clinical evidence that a lifetime of better calcium intake results in better bone density," ......"food first, then supplements," ........"Something simple like drinking milk, the primary dietary source of vitamin D, has declined over the past 30 years," he said. "Following current dietary guidelines could make a real difference, especially if followed over a lifetime."
 
Action Points

 
* Explain that women with a low dietary intake of calcium are at increased risk of fractures and osteoporosis.
 
* Note that for women with calcium intake above the lowest quintile, this study found little additional benefit for bone health, although some experts noted that many women still do not obtain adequate calcium.
 
Women with a low dietary intake of calcium are at increased risk of fractures and osteoporosis, Swedish researchers reported.
 
In a large prospective cohort study, women who started with the lowest dietary calcium were 18% more likely to suffer a fracture than those with an intake of about 700 mg a day, according to Eva Warensjo, PhD, of Uppsala University in Uppsala, Sweden, and colleagues.
 
But above that level, there was little additional benefit, they reported online in BMJ.
 
The implication is that, in order to prevent osteoporotic fractures, clinicians and public health authorities should focus on those with low calcium, "rather than increasing the intake of those already consuming satisfactory amounts," the researchers argued.
 
But outside experts said the study needs to be interpreted carefully before making changes to public policy or clinical practice.
 
"One swallow does not a spring make, and studies like this always need to be interpreted with caution," commented Nanette Santoro, MD, of the University of Colorado School of Medicine in Aurora, Colo.
 
"Women should not throw out their supplements just yet," Santoro said in an email to ABC News and MedPage Today.
 
But her advice for women, she said, would be to work more calcium-rich foods into the diet and to make sure they get enough vitamin D, which helps the body use calcium.
 
"The salient message is that if a little is good, more is not always better, so obsessively chomping calcium pills is not the way to go," Santoro said.
 
Indeed, most experts contacted by ABC News and MedPage Today said they advise patients to eat a healthy diet, including more dairy products than most people now get.
 
"The recommendation in the U.S., Canada, and France is for intake of 1,200 mg a day in total, including diet," said Michelle Warren, MD, of New York Presbyterian Hospital in New York City.
 
But many older adults don't drink or eat enough dairy products and may need supplements to get them to that level, she said in an email.
 
The issue is unclear, Warensjo and colleagues noted, as evidenced by national recommendations ranging from 700 mg a day in the U.K. to 1,300 a day in Australia and New Zealand.
 
To try to pin the matter down, they turned to the Swedish Mammography Cohort, a population-based cohort in Sweden established in 1987. The researchers linked food questionnaires at baseline and in 1997 with fracture rates from a national database.
 
And between 2003 and 2009, they asked a subcohort to have dual energy x-ray absorptiometry scanning, to give blood and urine samples, and to have their height and weight measured, as well as to fill out a third food questionnaire.
 
The researchers used the latter group to estimate the incidence of osteoporosis.
 
All told, 61,433 women born between 1914 and 1948 took part in the study and 5,022 participated in the osteoporosis cohort. Median follow-up was 19 years.
 
During follow-up, 14,738 (24%) of the women had a first fracture, 3,871 (6%) had a first hip fracture, and 20% of the subcohort developed osteoporosis.
 
The women were stratified according to their calcium intake, with the lowest quintile below 751 mg daily and the highest above 1,137. The middle group л those with an average intake of from 882 to 996 mg a day л was used as the reference group.
 
Warensjo and colleagues found that the risk of a first fracture was highest in the low intake group, with a rate of 17.2 per 1,000 person-years.
 
But in the four higher groups, there was little evidence of additional benefit with rates of 14.7, 14.0, 14.1, and 14.0 per 1,000 person-years, respectively, for the second through fifth quintiles, they reported.
 
The adjusted hazard ratio comparing the lowest quintile with the reference group was 1.18 (95% CI, 1.12 to 1.25). There were no other significant differences.
 
On the other hand, there was some evidence that those in the highest quintile were at slightly increased risk for a first hip fracture, although the researchers said the data should be interpreted with caution.
 
In the osteoporosis cohort, the researchers found, low calcium increased the risk and high calcium reduced it. The odds ratios, comparing the lowest and the highest quintiles with the reference group, were 1.47 and 0.84, respectively. The other quintiles were not significantly different from the reference group.
 
Keith-Thomas Ayoob, EdD, RD, of Albert Einstein College of Medicine in New York City, cautioned that the study as a whole needs to be looked at carefully.
 
"There's plenty of clinical evidence that a lifetime of better calcium intake results in better bone density," he told ABC News and MedPage Today in an email.
 
He noted that the study is largely based on questionnaires "and those self-reports are not always reliable tools." It's also possible that those who used supplements in the study did so because they perceived they were at risk, he said.
 
The advice for women should be "food first, then supplements," Ayoob said.
 
"Something simple like drinking milk, the primary dietary source of vitamin D, has declined over the past 30 years," he said. "Following current dietary guidelines could make a real difference, especially if followed over a lifetime."
 
But Charles Clark, Jr., MD, of Indiana University School of Medicine in Indianapolis, said, "Since most women in the age group at risk do not have adequate calcium in their diet, most will need calcium supplements."
 
A recent report from Institute of Medicine, he noted in an email, supported lower recommendations, and the Swedish study "adds to the current trend to lower calcium (and vitamin D) recommendations."
 
The researchers cautioned that the study might not apply outside of Sweden, but Clark noted that many Americans are of Nordic extraction. "This study is highly relevant to the U.S. population," he said.
 
-----------------------------------------
 
BMJ 2011; 342:d1473 doi: 10.1136/bmj.d1473 (Published 24 May 2011)
 
Dietary calcium intake and risk of fracture and osteoporosis: prospective longitudinal cohort study - pdf attached
 
Eva Warensjo , researcher,1,4 Liisa Byberg, researcher,1,4 Ha kan Melhus, professor,3,4 Rolf Gedeborg, associate professor,2,4 Hans Mallmin, professor,1 Alicja Wolk, professor,5 Karl Michae lsson, professor1,4 1Department of Surgical Sciences, Section of Orthopaedics, Uppsala University, Uppsala, Sweden 2Department of Surgical Sciences, Anaesthesiology and Intensive Care, Uppsala University, Uppsala, Sweden 3Department of Medical Sciences, Clinical Pharmacology, Uppsala University, Uppsala, Sweden 4Uppsala Clinical Research Centre, UCR, Uppsala University, Uppsala, Sweden 5Division of Nutritional Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden Correspondence to: E Warensjo eva.warensjo@surgsci.uu.se
 
Abstract
 
Objective - To investigate associations between long term dietary intake of calcium and risk of fracture of any type, hip fractures, and osteoporosis. Design - A longitudinal and prospective cohort study, based on the Swedish Mammography Cohort, including a subcohort, the Swedish Mammography Cohort Clinical.
 
Setting - A population based cohort in Sweden established in 1987.
Participants - 61 433 women (born between 1914 and 1948) were followed up for 19 years. 5022 of these women participated in the subcohort.
 
Main outcome measures - Primary outcome measures were incident fractures of any type and hip fractures, which were identified from registry data. Secondary outcome was osteoporosis diagnosed by dual energy x ray absorptiometry in the subcohort. Diet was assessed by repeated food frequency questionnaires.
 
Results - During follow-up, 14 738 women (24%) experienced a first fracture of any type and among them 3871 (6%) a first hip fracture. Of the 5022 women in the subcohort, 1012 (20%) were measured as osteoporotic. The risk patterns with dietary calcium were non-linear. The crude rate of a first fracture of any type was 17.2/1000 person years at risk in the lowest quintile of calcium intake, and 14.0/1000 person years at risk in the third quintile, corresponding to a multivariable adjusted hazard ratio of 1.18 (95% confidence interval 1.12 to 1.25). The hazard ratio for a first hip fracture was 1.29 (1.17 to 1.43) and the odds ratio for osteoporosis was 1.47 (1.09 to 2.00). With a low vitamin D intake, the rate of fracture in the first calcium quintile was more pronounced. The highest quintile of calcium intake did not further reduce the risk of fractures of any type, or of osteoporosis, but was associated with a higher rate of hip fracture, hazard ratio 1.19 (1.06 to 1.32).
 
Conclusion - Gradual increases in dietary calcium intake above the first quintile in our female population were not associated with further reductions in fracture risk or osteoporosis.
 
Introduction
 
Osteoporotic fractures are frequent in elderly populations, especially in women, and are associated with high healthcare costs and individual suffering. With ageing populations, the burden of osteoporotic fractures on society will increase in the coming years1 and the prevention of osteoporotic fractures is therefore a major public health issue. The importance and optimal level of calcium intake to compensate for skeletal calcium losses1 and for the prevention of osteoporosis and fractures have been much debated and remain unclear. This is reflected by the wide range of daily calcium recommendations for individuals older than 50 years: at present 700 mg in the UK,2 800 mg in Scandinavia,3 1200 mg in the United States,4 and 1300 mg in Australia and New Zealand.5
 
It is problematic to make recommendations regarding calcium intake based on the results from clinical trials and previous cohort studies. Meta-analyses of randomised trials found that supplemental calcium gave modest6 or no reduction7 in risk of fracture. Both the habitual dietary intake of calcium and vitamin D status may affect the outcome and are rarely accounted for in the design of calcium supplementation trials.8 Nor do observational data provide clear evidence, as emphasised by meta-analyses with differing results, on the association between calcium intake and fracture risk.9 10 To improve precision, prospective studies with repeated dietary surveys and large numbers of participants are needed.
 
Against this background, we aimed to investigate associations between long term dietary intake of calcium with risk of fracture of any type, with hip fractures, and with osteoporosis, in a large, population based prospective study of Swedish women.
 
Results
 
Table 1 shows the characteristics of the study participants by quintiles of dietary calcium intake. With increasing quintiles of calcium intake the reported intake for most other nutrients also increased. Small differences were present for calcium supplement use, comorbidity, educational level, smoking status, and physical activity level between quintiles.
 
During a median of 19.2 years of follow-up and 996 800 person years at risk, 14 738 women (24%) experienced any type of first fracture and 5043 (8%) experienced two or more fractures. For hip fractures the corresponding numbers were 3871 (6%) and 1368 (2%) during a median of 19.8 years of follow-up and 1 069 980 person years at risk. In the subcohort, 1012 (20%) of the participants were classified as osteoporotic.
 
There was an apparent decrease in risk for every 300 mg increase of dietary calcium intake (table 2) but the associations were non-linear (P< 0.001 for calcium intake as a quadratic term). The rate of first fractures and prevalence of osteoporosis were highest in the lowest quintile of dietary calcium intake (table 2). Within this quintile, compared with the third (table 2), the multivariable adjusted hazard ratio for any fracture was 1.18 (95% confidence interval 1.12 to1.25) and for hip fracture 1.29 (1.17 to 1.43). These estimates were somewhat weaker when we analysed multiple fracture events (table 2). Within the lowest quintile, the risk of fracture increased for every 100 mg decrease in calcium intake, with a multivariable adjusted hazard ratio of 1.08 (1.04 to 1.11) for any first fracture and 1.07 (1.01 to 1.13) for first hip fracture (P=0.19 and P=0.32, respectively, for the quadratic term of calcium intake). The lowest quintile of dietary calcium intake was also associated with an increased risk of osteoporosis (adjusted odds ratio 1.47, 95% confidence interval 1.09 to 2.00).
 
In the highest quintile of calcium intake, the rate of fracture of any type and the rate of osteoporosis were similar to those in the third quintile (table 2), whereas the hip fracture rate was raised in the highest quintile (hazard ratio 1.19, 95% confidence interval 1.06 to 1.32). The non-linear association between dietary calcium intake and first hip fracture rate is further illustrated by the spline curve in fig 2. Neither quintiles of total calcium intake (including supplements) nor the use of calibrated dietary calcium intake essentially changed the estimated hazard ratios for fracture, although the higher fracture rate at low intake levels became more pronounced (table 3). The results also remained essentially unchanged after exclusion of women with a previous fracture of any type before the hip fracture event after baseline, or when the analysis was restricted to specific age intervals (<70, 70-80, >80 years).
 
Vitamin D intake modified the associations between calcium intake and the rate of fractures of any type (Pinteraction = 0.01) and at the hip (Pinteraction = 0.02), but not the odds of osteoporosis. Although the association between dietary calcium intake and fracture rate was similar both with a vitamin D intake below and above the median, there was a tendency towards a higher hip fracture rate within the lowest quintile of dietary calcium intake in combination with a low dietary vitamin D intake (table 4).
 
Discussion
Principal findings

 
These findings show an association between a low habitual dietary calcium intake (lowest quintile) and an increased risk of fractures and of osteoporosis. Above this base level, we observed only minor differences in risk. The rate of hip fracture was even increased in those with high dietary calcium intakes.
 
Strengths and weaknesses of the study
 
Strengths of our study include the population based prospective design with both fractures and osteoporosis as outcomes, and repeated measurements of calcium intake, together with a large number of potential covariates. Incident fractures were traced though national healthcare registries and deterministic record linkage, permitting almost complete case ascertainment. We have adjusted for several important covariates such as nulliparity, smoking, socioeconomic status, physical activity, nutrients other than calcium, educational level, and comorbidity, but residual confounding still remains a possible limitation. Dietary assessment methods are prone to a number of limitations, affecting both the precision and accuracy of the measurement. A food frequency questionnaire is used to assess the habitual intake of diet in larger studies, and a recent review concluded that it was a valid method for assessing dietary mineral intake, particularly for calcium.33 The food frequency questionnaire may overestimate calcium intake22 and the threshold of calcium intake detected in our analyses may therefore be somewhat exaggerated. Moreover, misclassification of study participants according to calcium intake may have introduced a conservative bias to our estimates of association. The observational study design precludes conclusions regarding causality. Our results might not apply to other people of different ethnic origins or to men.
 
Strengths and weaknesses in relation to other studies
 
The large size of this study enabled us to define a threshold of dietary calcium intake with better precision than in previous studies. The results from previous prospective cohort studies on the relation between dietary calcium intake and fracture risk are contradictory. British women older than 50 years had an increased risk of fractures (self reported five years after study entry) at calcium levels below 700 mg compared with a reference level of 1200 mg.34 Other large prospective cohort studies9 35 21 and one meta-analysis7 reported no association between calcium intake and fracture risk.
 
Vitamin D enhances the renal conservation and intestinal absorption of calcium.1 Our results suggest that the optimal level for calcium intake for the prevention of osteoporotic fracture is higher when dietary vitamin D intake is low. This finding has not been shown21 or investigated35 in previous prospective studies but accords with findings in randomised co-supplementation trials.6 7
 
Circulating vitamin D levels are only to a lesser extent determined by the dietary intake of vitamin D.36 37 38 Nonetheless, dietary calcium intake was only associated with bone mineral density in women with serum vitamin D values less than 50 nmol/L in the large NHANES III cohort.39
 
Possible explanations and implications
 
The present results may reflect a situation when a moderate intake of calcium combined with adequate intake of other micronutrients is sufficient to meet the structural and functional demands of the skeleton. High levels of intake did not further decrease the rate of fracture, and might even increase the rate of hip fractures, although this result should be cautiously interpreted. The finding might be explained by a reverse causation phenomenon; that is, women with a higher predisposition for osteoporosis may have deliberately increased their intake of calcium rich foods. We tried to avoid this bias by restricting the analysis to women with first fracture events. If it exists, this bias would probably have also been reflected in a higher rate of other types of fractures, not only hip fractures. Furthermore, few participants had knowledge of their bone mineral density (which could have influenced the dietary habits) since general screening of osteoporosis with bone mineral density scans does not exist in Sweden. Moreover, use of supplemental calcium has been associated with higher rates of hip fracture both in a cohort study40 and in randomised controlled trials.7 8 41 The high calcium intake can reduce the enlargement of the appendicular bones that generally occurs with ageing as a mechanical compensation for a decline in bone mineral density.8 Furthermore, high calcium doses slow bone turnover and also reduce the number of active bone remodelling sites.42 This situation can lead to a delay of bone repair caused by fatigue, and thus increase the risk of fractures independent of bone mineral density.42 The two dimensional DXA measurement precluded us from accurately determining associations between calcium intake and bone size, and specific associations with cortical and trabecular bone.43
 
Our observational data suggest that in the prevention of osteoporotic fractures emphasis should be placed on individuals with a low intake of calcium rather than increasing the intake of those already consuming satisfactory amounts, as previously argued by Prentice.44 Further research is needed-for instance, a randomised study with a factorial design that considers low baseline levels of calcium in combination with calcium supplements.
 
Conclusions
 
Incremental increases in calcium intake above the level corresponding to the first quintile of our female population were not associated with a further reduction of osteoporotic fracture rate.
 
 
 
 
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