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Australian Dietary Guidelines submission

ID: 
25
Personal Details
Organisation Name: 
Osteoporosis Australia
Online comments
Specific comments: 
Chapter 2- Eat a wide variety of nutritious foods

2.5.2.3 Other Conditions

 

This section currently reads as follows:

“The traditional nutritional rationale for the inclusion of dairy foods such as milk, cheese and yoghurt is their high calcium content and the positive relationship between calcium and bone mass [9].

Bone mineral density: Recent evidence suggests that consumption of dairy foods (particularly milk) is associated with improved bone mineral density (Grade C, Section 5.1 in Evidence Report [14]) [399, 402-407] but this is contradicted by evidence suggesting that less than one serving of milk per day during adult life is not associated with risk of osteoporotic or hip fracture (Grade C, Section 5.2 in Evidence Report [14]) [408, 409].”

 

We recommend modification of the statement citing the contradictions as it is not a true representation of the scientific findings in that this study relates only to calcium intake from milk and does not take into account calcium from other dietary sources, including other dairy foods and calcium supplements and as such it downplays the importance of calcium in the maintenance of bone health. 

 

 Kanis et al  (your reference 409) clearly states “One limitation of the study is the construct of the question concerning calcium intake, which differed somewhat between cohorts and at best lacks precision and accuracy. Although total calcium intake was recorded in two of the studies and would have included calcium supplements, in other cohorts calcium supplements may have confounded the relationship between intake of milk and total intake of calcium. The effect of this heterogeneity is likely to weaken any association. Moreover, we were unable, using the construct of the question, to examine intakes of calcium lower than 500 mg daily, so that we cannot exclude a threshold effect as has been shown in case control studies for hip fracture risk [30,40], albeit with a threshold similar to the one that we used to dichotomise milk intake. Finally, we neglected sources of calcium intake other than milk, including cheese and yoghurt, and variations in dietary vitamin D or sunlight exposure [30,40,41]. This study should not, therefore, be misinterpreted as suggesting no causative role of calcium in the causation of fractures, nor a role for calcium nutrition in their prevention. Indeed, the association of an increased risk of osteoporotic fracture in the elderly is consistent with an important role for calcium in the elderly in whom other risk factors are more prevalent including immobility and lack of sunlight exposure.”

 

Additionally, a recent large prospective longitudinal cohort study (Warensjö, E., et al., Dietary calcium intake and risk of fracture and osteoporosis: prospective longitudinal cohort study. BMJ. 2011. 342: d1473.) showed that dietary calcium intakes below <751 mg per day were associated with an increased risk of first hip fracture, any first fracture and osteoporosis. Overall, low diet calcium intakes, mainly due to low dairy consumption, can be considered a risk factor for both low bone mineral density and fractures related to osteoporosis, and we believe it is appropriate to represent this fairly in the next edition of the dietary guidelines.

Alternative wording that may be considered follows:

The traditional nutritional rationale for the inclusion of dairy foods such as milk, cheese and yoghurt is their high calcium content and the positive relationship between calcium and bone mass [9].

Bone mineral density: Recent evidence suggests that consumption of dairy foods (particularly milk) is associated with improved bone mineral density (Grade C, Section 5.1 in Evidence Report [14]) [399, 402-407] and a recent large prospective longitudinal cohort study showed that dietary calcium intakes below <751 mg per day were associated with an increased risk of first hip fracture, any first fracture and osteoporosis (Grade C) [Warensjö, E., et al]. There is some contradictory evidence suggesting that less than one serving of milk per day during adult life is not associated with risk of osteoporotic or hip fracture (Grade C, Section 5.2 in Evidence Report [14]) [408, 409]. Overall, low diet calcium intakes, mainly due to low dairy consumption, can be considered a risk factor for both low bone mineral density and fractures related to osteoporosis.

Chapter 2- Eat a wide variety of nutritious foods

2.5.3 How drinking milk and eating yoghurt, cheese and/or alternatives may improve health outcomes

 

This section currently reads as follows:

"Two proposed mechanisms link the consumption of milk, yoghurt and cheese products with a reduction in cardiovascular risk. Firstly, the consumption of milk, yoghurt and cheese products has been linked to an increase in the levels of high density lipoprotein (HDL) cholesterol [410, 411]. Secondly, there is evidence of an inverse relationship between milk, yoghurt and cheese consumption (especially milk) and blood pressure [412] which might be mediated by calcium modulation of endothelial function [413]. Calcium from foods may be preferable to calcium from some supplements. A recent meta-analysis of the effect of calcium supplementation on myocardial infarction and cardiovascular events [414] suggested that calcium supplements, without co-administered vitamin D, were associated with an increased risk of myocardial infarction. The same group have more recently reported a similar effect from calcium supplements with vitamin D [415]. However, the effect of an equivalent dose of calcium from milk, yoghurt and cheese products has a much smaller effect than calcium supplements on the proposed risk factor, namely raised serum calcium levels [416].

There may be a negative association between calcium and blood pressure although this is variable, depending on other dietary factors, and it has been suggested that calcium supplementation may lower blood pressure only in people with a relatively high salt intake [417].

Several reasons have been suggested for the lack of an association between a low consumption of milk and increased risk of osteoporotic fracture of the hip. For example it has been suggested that women who consumed higher quantities of milk chose to do so because they were known to be at an elevated risk of osteoporosis or that milk intake during childhood was more important [418].

A randomized control trial of overweight children found that 200mL of milk per day combined with nutrition education reduced consumption of sugar-sweetened drinks and increased lean body mass [419]."

 

We recommend deletion of the following sentences: “A recent meta-analysis of the effect of calcium supplementation on myocardial infarction and cardiovascular events [414] suggested that calcium supplements, without co-administered vitamin D, were associated with an increased risk of myocardial infarction. The same group have more recently reported a similar effect from calcium supplements with vitamin D [415]. However, the effect of an equivalent dose of calcium from milk, yoghurt and cheese products has a much smaller effect than calcium supplements on the proposed risk factor, namely raised serum calcium levels [416].”

 

The studies cited to support these statements represent a re-analysis of data collected in the Women’s Health initiative by one group of researchers (Bolland et al) While their published results suggest a possible increase in myocardial infarction, the validity of the methods have been widely questioned and are at odds with two large studies (one in combination with Vitamin D)  which were designed to investigate this type of adverse effect have reaffirmed that there is no risk ( Lewis JR, Calver J, Zhu K, Flicker L, Prince RL. Calcium supplementation and the risks of atherosclerotic vascular disease in older women: results of a 5-year RCT and a 4.5-year follow-up. J Bone Miner Res 2011;26:35-41.; 5. Rejnmark L, Vestergaard P, Mosekilde L. Calcium supplements do not increase risk of cardiovascular disease: Results from a randomized controlled trial. Bone 2011: 48: OC34.)

 

A further study was recently published in Osteoporosis International (Nordin,BEC et al; The Calcium Scare – what would Austin Bradford Hill have thought?; Osteoporosis Int (2011) 22:3073-3077) which conducted a critical examination of the metaanalysis conducted by Bolland et al and found the analysis was subject to several limitations some of which included: non-adherance to clinical protocol, multiple endpoint testing and failure to correctly adjust for endpoint ascertainment. Additionally the main risk factors for myocardial infarction were not available for 65% of the participants and none of the trials included in the meta-analysis had cardiovascular disease as an endpoint. Overall, the conclusion was that the meta-analyses do not provide evidience that calcium supplementation increases the risk of heart attack; and in the absence of plausible biological basis and the support of a major prospective study it would be scientifically unbalanced and inappropriate to make reference to the Bolland studies in the Australian Dietary Guidelines

 

The section, amended in accordance with our recommendation would read as follows:

 

 

Two proposed mechanisms link the consumption of milk, yoghurt and cheese products with a reduction in cardiovascular risk. Firstly, the consumption of milk, yoghurt and cheese products has been linked to an increase in the levels of high density lipoprotein (HDL) cholesterol [410, 411]. Secondly, there is evidence of an inverse relationship between milk, yoghurt and cheese consumption (especially milk) and blood pressure [412] which might be mediated by calcium modulation of endothelial function [413]. Calcium from foods may be preferable to calcium from some supplements.

There may be a negative association between calcium and blood pressure although this is variable, depending on other dietary factors, and it has been suggested that calcium supplementation may lower blood pressure only in people with a relatively high salt intake [417].

Several reasons have been suggested for the lack of an association between a low consumption of milk and increased risk of osteoporotic fracture of the hip. For example it has been suggested that women who consumed higher quantities of milk chose to do so because they were known to be at an elevated risk of osteoporosis or that milk intake during childhood was more important [418].

A randomized control trial of overweight children found that 200mL of milk per day combined with nutrition education reduced consumption of sugar-sweetened drinks and increased lean body mass [419].

 

Page reviewed: 3 January, 2013