Appendix 2: Processes for preparing nutrient reference values

The assessment process

Reviewers completed a pro-forma that asked them to assess the suitability of the US:Canadian DRI recommendations for adoption in Australia and New Zealand, taking into consideration:

  • the completeness and currency of the evidence base

  • the interpretation of the evidence

  • the selection of indicators for estimating requirements

  • the justifiability of recommendations for various age and gender categories

  • whether the needs of special groups were considered, including vegetarians, formula-fed versus breast-fed babies, cultural and racial groups, cigarette smokers, oral contraceptive users, those with high alcohol use or drug use, athletes, tropical dwellers or any other special group

  • interactions with other nutrients or non-nutrients including the issue of bioavailability

  • whether the effect of other factors had been considered (socio-economic status of study populations, customary intake of other competing nutrients or interfering/enhancing factors, lifestyle characteristics such as physical labour, prevalence of disease, climatic effects etc)

  • whether dietary patterns of Australia and New Zealand were sufficiently different from those of the US:Canada to affect any of the recommendations (particularly relevant to the AI and AMDR recommendations)

  • whether the UL was adequately addressed and whether it was appropriate for Australia and New Zealand

  • whether there was evidence for a protective effect for chronic disease at levels of intake higher than RDI levels of intake

  • whether there was evidence for a chronic disease-promoting effect of higher than RDI levels

  • whether they had any other considerations that they wished to raise that would affect recommendations for Australia and New Zealand

  • recommendations from other countries such as the UK, European countries or bodies such as the FAO:WHO or European Commission.

They were asked to provide an evidence-based assessment of the key papers used in the US:Canadian DRI review to derive the recommendations and to provide an analysis of any key missing papers or key papers published since the DRI review of that nutrient, using the NHMRC levels of evidence (see below) where possible or relevant.

Finally, they were asked to state whether they thought that Australia and New Zealand should adopt, adopt with minor changes, adopt with substantial changes, or reject, the US and Canadian recommendations in terms of their suitability for use in Australia and New Zealand, and to summarise their overall recommendations.

The expert reviews and recommendations together with the US:Canadian DRI reviews and those of other countries and health bodies were then considered by members of the Working Party who made the recommendations contained herein. The evidence tables and rationales for variation from the recommendations of the US:Canadian DRI reviews have been published separately as an Appendix to this report.

The evidence base

There are several initiatives underway around the world to develop an evidence-based approach to nutrition and health issues. This has generally been in response to the need for proof in relation to health claims for food components (ANZFA 2000, Codex Alimentarius Commission 2000, Truswell 2001, US FDA 1999). A set of proposed levels of evidence for food or health claims has been developed by Food Standards Australia and New Zealand (formerly Australian New Zealand Food Authority), which is similar to, but somewhat broader in scope than, the set of NHMRC levels of evidence which was primarily designed for the development of clinical guidelines.

It was felt that the 1999 NHMRC designation of levels of evidence for clinical practice was applicable to assessing the evidence base for the development of the NRVs. Although the NHMRC system of evidence assessment has flexibility in the assignment of evidence levels to accommodate the type of question being asked (eg whether the question relates to the effectiveness of intervention or prevalence), a single set of evidence levels was used as the basis of the evidence assessment for clarity (see below).

The NHMRC's Levels of Evidence:

I Evidence obtained from a systematic review of all relevant randomised controlled trials.

II Evidence obtained from at least one properly designed randomised controlled trial.

III-1 Evidence obtained from well-designed pseudo-randomised controlled trials (alternate allocation or some other method).

III-2 Evidence obtained from comparative studies (including systematic reviews of such studies) with concurrent controls and allocation not randomised, cohort studies, case-control studies, or interrupted time series with a control group.

III-3 Evidence obtained from comparative studies with historical control, two or more single arm studies, or interrupted time series without a parallel control group.

IV Evidence obtained from case series, either post-test or pre-test/post-test.

Source: A Guide to the Development, Implementation and Evaluation of Clinical Practice Guidelines ( NHMRC 1999).

There are six levels of evidence. Level I is based on a systematic review of all relevant RCTs. Level II is based on evidence obtained from at least one properly designed RCT. With the possible exception of calcium, there are few Level I or Level II nutrient intervention trials that assess adequacy of nutrient intake in relation to deficiency states, although a number of nutrient-supplement trials have been undertaken in relation to chronic disease aetiology.

Some of the studies used to set nutrient requirements fall within Level III or Level IV, that include cohort studies, case-control studies and comparative ecological studies with historical controls or case series. However, much of the evidence comes from animal or human experimental studies that do not fall within these categories, or observational or cross-sectional survey data (eg all the recommendations for infants aged 0-6 months are based on the composition of milk from healthy mothers and a significant amount of the evidence for the UL comes from individual case reports of excessive intakes related to accidentally high intakes or special conditions such as parenteral feeding).

The NRVs were developed from a process of comprehensive, rather than systematic, review of the literature. A summary of the search strategies and key evidence used to set recommendations is provided in the Evidence Appendix.

The NHMRC states that "a decision should be made about what is feasible and appropriate in a given situation and the extent to which reasonable standards have been met by the available body of evidence". Although the NRVs are evidence-based where possible, there are generally very limited data on which to base recommendations. Life-stage and gender were considered to the extent possible during assessment of the literature, but for many nutrients and for many age, gender and life-stage categories, requirements had to be estimated from one category on the basis of metabolic body weight, energy requirements, potentially decreased absorptive capacity, activity levels, additional needs for foetal growth or production of breast milk etc rather than being derived directly from experimental data.

Apart from studies of frank deficiency disease, few studies address the effects of inadequate intake on specific health indicators. While the recommendations are often given as single rounded numbers, it is acknowledged that these values may imply a precision not fully justified by the available human data. Nevertheless, the values recommended represent our best attempt to identify the requirements of the various age, gender and life-stage groups.

It is also recognised that the requirements for some nutrients can be affected by the intake of other nutrients and that health outcomes are often the result of an interplay between various nutrients (and/or other non-nutritional factors), rather than the effect of any single nutrient. Where known interactions exist, these have been taken into account in assessment of the data.

In his introduction to the publication of the 1981-1989 RDIs for Australia (Truswell et al 1990) Truswell wrote

No one who hasn't been responsible for producing RDI figures can realise how short we are of adequate original, numerical data. As we worked through 21 nutrients in 9 years, time and again we have said "we just don't know the answer to that question", or "if only several countries would collaborate in research to give us a proper picture of the distribution of numbers about that" and, of course, "what a pity we have no Australian (New Zealand) data on this".

In the 20 or so years since the previous RDIs were determined, new studies have been added to the data base. However, the available numerical data remain extremely limited for most nutrients, such that for some, we are forced to rely on one or two limited studies from which to derive the estimates. The limitations on data are particularly obvious for infants, children and adolescents, as most experimentation is carried out on adult populations. These limitations need to be borne in mind when applying the resulting reference values to the assessment of dietary adequacy for individuals or groups.

The consultation process

After the Working Party had made its initial deliberations, the draft recommendations were submitted for public consultation in Australia and New Zealand between December 2004 and March 2005, allowing three months for consultation. Notification in Australia was published in the Commonwealth Government Gazette and on the NHMRC website as well as through direct notification of key bodies. The NZ Government ensured notification of key bodies and the public.

Copies of draft documents and supporting information were made available free of charge from the Office of NHMRC and on the NHMRC website. In addition, notices were included in other publications and media such as newspapers and radio. During the submission period, two workshops were held in each of Australia and New Zealand with health professionals, representatives of the food industry and end-users. They included consideration of optimal methods for dissemination, including electronic access. Each of these workshops was attended by 40-60 stakeholders.

Sixty-four submissions were received and considered by the Working Party in May 2005. The document was amended where relevant in response to the submissions, independently reviewed and assessed against the NHMRC criteria for guideline development. The document was technically edited before final submission to the NHMRC and Australian and New Zealand Governments for approval.

Dissemination and implementation

Upon endorsement of the Nutrient Reference Values for Australia and New Zealand by the NHMRC, the Australian Government Department of Health and Ageing and the New Zealand Ministry of Health will manage the adoption of the NRVs through appropriate Government processes in their respective countries.

Media releases, including a question and answer section, will be issued in Australia and New Zealand. The main report, evidence appendix and summary report will be made available on the NHMRC and Ministry of Health websites.

Notification of availability of the final report and details of how to access both electronic and hard copies will be sent to all expert reviewers, those who made submissions regarding the December 2004 consultation draft and attendees at the consultation workshops in both countries.

The Australian Government Department of Health and Ageing and the New Zealand Ministry of Health will then:

  • advertise release of, and prepare articles about, the Nutrient Reference Values for Australia and New Zealand in their own newsletters ands relevent publications and those of various stakeholder groups

  • prepare presentations on the new NRVs for conferences and seminars

  • introduce a program of progressive review and updating of existing nutrition documents and health professional education materials that include, or are based on, the NRVs

  • advocate the use of the NRVs outside the lead ministries, including to the wider health sector, other government agencies, the education sector, non-government organisations, food industry groups, dietitians and nutritionists.

In keeping with the NHMRC publications review policy, it is expected that the process of reviewing the NRVs will commence within five years of endorsement of the publication by the NHMRC.

Submissions in the consultation process

From Australia

Professor Cres Eastman Institute of Clinical Pathology and Medical Research

Professor Stewart Truswell University of Sydney

Dr Stephen Corbett Sydney West Area Health Service

Ms Jen Savenake Tasmanian Department of Health and Human Services

Mr Peter Liu DSM Nutritional Products Australia Pty Ltd

Ms Barbara Eden National Heart Foundation of Australia

Ms Gemma McLeod Fremantle Hospital

Mrs Jenni Cooper H.J. Heinz Company Australia Ltd

Ms Alison Stewart Southern Health

Dr Beverley Wood -

Mr Philip Juffs, Princess Alexandra Hospital
Ms Helen Porteous

Ms Trish Guy Sanitarium Health Food Company

Ms Adrienne Mouritz -

Mr Bill Shrapnel Shrapnel Nutrition Consulting Pty Ltd

Dr Jeanette Fielding Wyeth Australia Pty Ltd

Ms Christine Josephson, Logan Hospital
Ms Brigitte Corcoran,
Ms Clare Byrne,
Ms Alice Mo,
Ms Claire Kelly,
Ms Leah Cain,
Ms Anneli Reeves,
Ms Annabelle Stack

Dr Jill Sherriff Curtin University of Technology

Ms Ingrid Coles-Rutishauser -

Dr Trevor Beard Menzies Research Institute

Professor Christopher Nordin Institute of Medical and Veterinary Science

Ms Trish Griffiths BRI Australia Ltd

Dr Anita Lawrence Dairy Australia

Ms Veronica Graham Victorian Department of Human Services

Ms Lynn Riddell Deakin University

Dr Deborah Kerr Curtin University of Technology

Dr Vicki Flood NSW Centre for Public Health Nutrition

Ms Nerida Bellis-Smith Dietitians Association of Australia

Dr Peter Abbott Food Standards Australia New Zealand

Ms Kellie Teys Compass Group (Australia) Pty Ltd

Dr David Filby South Australian Department of Health

Dr Barbara Meyer University of Wollongong

Dr David Roberts Australian Food And Grocery Council

Dr Dorothy Mackerras Menzies School of Health Research

Ms Natalie Obersky -

A/Professor Susan Ash Queensland University of Technology

Professor Andrew Sinclair Royal Melbourne Institute of Technology

Ms Jackie Steele Queensland Health

Dr Denise Robinson NSW Health

Ms Judith Myers Royal Children's Hospital

A/Professor David Colquhoun The University of Queensland

Ms Wendy Morgan Innovations and Solutions

Mr Terry Slevin The Cancer Council Australia

Dr Manny Noakes CSIRO Health Sciences and Nutrition

Dr Graham Lyons University of Adelaide

From New Zealand

Mr John Gibson Age Concern Wellington Inc.

A/Professor Elaine Rush Auckland University of Technology

Ms Madeleine Price Canterbury District Health Board

Professor Rosalind Gibson University of Otago

Mrs Winsome Parnell University of Otago

Mr Graham Atkin Fluoride Action Network (NZ) Inc.

Ms Janelle Mackie Canterbury District Health Board

Mrs Nanda Kadayji -

Ms Claire Walker Public Health South

Mr Robert Quigley Cancer Society of New Zealand

A/Professor Juergen Koenig Massey University

Ms Carole Inkster New Zealand Food Safety Authority

Dr Sheila Skeaff University of Otago

Mr John Robertson New Zealand Juice and Beverage Association Inc

Ms Joan Wright Fonterra Co-operative Group Ltd

Ms Helen Wallwork New Zealand Dietetic Association

Dr Nelofar Athar Food Industry Science Centre

Mr David Roberts The National Heart Foundation of New Zealand

A/Professor Murray Skeaff University of Otago

From the United Kingdom

Mr Stephen Taylor Frenchay Hospital