Do We Need a Dietary Reference Intake for Bioactives?
The Dietary Reference Intakes were developed in the 1990s to assist nutrition professionals in determining dietary adequacy. The five types of reference intakes (Estimated Average Requirement, Recommended Dietary Allowance, Tolerable Upper Limit, Average Intake, and Acceptable Macronutrient Distribution Ranges) are used to work out whether populations or individuals are consuming essential nutrients within a range least likely to be associated with deficiency or toxicity. These reference intakes are also used for nutrition labelling on food product packages.
Importantly, the reference intakes were developed only with essential nutrients: the vitamins, minerals, and macronutrients. The health outcomes used as desirable endpoints tended to relate to acute rather than chronic illnesses, as well. For example, vitamin C reference intakes are designed to prevent scurvy, however greater intakes of vitamin C over the lifespan may improve cardiovascular health (see review from May and Harrison). For other bioactive compounds, such as certain fatty acids, carotenoids and phytochemicals, there is neither a reference intake nor has essentiality been determined, yet their intake may be beneficial for long term good health, as summarized by Howes and Simmonds. Recently, Lupton and co-workers summarize the results of a conference that explored how to develop reference intakes for dietary bioactive components that are important for human health.
The authors defined seven reasons why it would be beneficial to have reference intakes for bioactives:
1. Many studies have already shown that bioactives can benefit human health
2. There is considerable ongoing research into dietary bioactives
3. Consumers are interested in changing their diets if there is likely to be a health benefit
4. Assigning reference intakes to bioactives highlights its importance in the diet, which can guide nutrition policy
5. The process used to define reference intakes sets an example, which can raise the quality of science into bioactives
6. A transparent process reassures nutrition professionals and the public that recommendations are science-based
7. Setting a recommended intake highlights dietary shortfalls and provides a goal for nutrition interventions and education
The authors use the example of the omega-3 long chain polyunsaturated fatty acids DHA and EPA. These two compounds are conditionally essential, and there are reference intakes developed for infants. Various countries and organizations have also proposed their own recommended intakes. However, there are no clear Reference Intakes for adults despite compelling evidence that they improve cardiovascular health (Calder). The authors suggest a process by which a NRV-NCD (Nutrient Reference Value-Non-Communicable Disease) can be set for dietary bioactives. Instead of a Tolerable Upper Limit, a highest observed intake (HOI), which can be defined when no adverse health effects have been identified, could be an appropriate means of establishing maximum intake levels.
There are potential benefits to public health policy if the role of dietary bioactive components in human health is intensively scrutinized and a reference intake for good health can be defined.
Lupton, J.R.; Blumberg, J.B.; L’Abbe, M.; LeDoux, M.; Rice, H.B.; Schacky, C.; Yaktine, A.; Griffiths, J.C. Nutrient reference value: Non-communicable disease endpoints—a conference report. European Journal of Nutrition 2016, 1-10, 10.1007/s00394-016-1195-z.
Calder PC (2012) Mechanisms of action of (n-3) fatty acids. J Nutr 142:592S–599S. http://www.ncbi.nlm.nih.gov/pubmed/22279140
Howes MJ, Simmonds MS. The role of phytochemicals as micronutrients in health and disease. Curr Opin Clin Nutr Metab Care. 2014 Nov;17(6):558-66. doi: 10.1097/MCO.0000000000000115. http://www.ncbi.nlm.nih.gov/pubmed/25252018
May James M. and Harrison Fiona E.. Antioxidants & Redox Signaling. December 2013, 19(17): 2068-2083. doi:10.1089/ars.2013.5205. http://online.liebertpub.com/doi/abs/10.1089/ars.2013.5205