Recommended Dietary Intakes – Do You Need Supplements?

by Paul Rogers on November 13, 2008

Photo by Untitled Blue

Photo by Untitled Blue

Here’s a quick definition of RDIs — or RDAs as they are called in some countries.

Recommended Dietary Intakes (RDIs) (or allowances, RDA) are the levels of intake of essential nutrients considered, in the judgment of national health and nutrition authorities on the basis of available scientific knowledge, to be adequate to meet the known nutritional needs of practically all healthy people.

RDIs are given for vitamins, minerals, protein and some fats, and for different life stages, and pregnancy, and are usually daily quantities. They represent the needs for sustenance and avoiding deficiency disease.  See examples for Australia and the US.

Now that sounds simple enough, but unfortunately the RDIs and other measures of nutritional adequacy are widely misunderstood. That definition above does not imply that the RDIs are the “minimum” quantity required to stave off malnutrition or starvation.

In calculating RDIs, a safety margin is used so that biological differences from person to person can be accommodated. It may be that some individuals have less of a margin than others, but overall, the RDIs and RDAs are designed to exceed the minimum requirements for just about everyone, significantly. The idea that they are minimum values finds great comfort in the vitamin and mineral supplement industry of course.

Optimising Diets for Chronic Disease Risk

 Even so, there is recognition that higher intakes may help prevent some chronic diseases. To be fair, this is likely to be where misunderstandings occur. For example, the RDI for vitamin C is 45 milligrams/day, yet the suggested target for reducing chronic disease risk is 220 milligrams/day — quite a difference. Folate is another example where the suggested dietary target or SDT is much higher than the RDI.

Other Standards in Nutrient Reference Values

Although terminology can differ from country to country, here is a full list of acronyms worth noting within the broad range of nutrient reference value (NRV) or dietary reference intake (DRI) standards as applicable in the US, Canada and Australia based on the Institute of Medicine proceedings.

  • EAR (Estimated Average Requirement). A daily nutrient level estimated to meet the requirements of half the healthy individuals in a particular life stage and gender group.
  • RDI (Recommended Dietary Intake). The average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97–98 per cent) healthy individuals in a particular life stage and gender group.
  • AI (Adequate Intake – used when a recommended dietary intake cannot be determined). The average daily nutrient intake level based on observed or experimentally-determined approximations or estimates of nutrient intake by a group (or groups) of apparently healthy people that are assumed to be adequate.
  • EER (Estimated Energy Requirement). The average dietary energy intake that is predicted to maintain energy balance in a healthy adult of defined age, gender, weight, height and level of physical activity, consistent with good health. In children and pregnant and lactating women, the EER is taken to include the needs associated with the deposition of tissues or the secretion of milk at rates consistent with good health.
  • UL (Upper Level of Intake). The highest average daily nutrient intake level likely to pose no adverse health effects to almost all individuals in the general population. As intake increases above the UL, the potential risk of adverse effects increases.
  • AMDR (Acceptable Macronutrient Distribution Range). An estimate of the range of intake for each macronutrient for individuals (expressed as per cent contribution to energy), which would allow for an adequate intake of all the other nutrients whilst maximising general health outcomes.
  • SDT (Suggested Dietary Target). A daily average intake from food and beverages for certain nutrients that that may help to prevent chronic disease.

Dietary Supplements

Supplementation has a role to play, but it needs to be done with caution, restraint and knowledge. The bottom line is that there will be individuals and population groups that do not meet the RDIs for individual nutrients.

  • This can result from poor nutrition practices or even special diets poorly implemented. Low-carbers could be short on fibre and vitamin E; vegans on zinc, iron and B12; and very low-fat dieters on long chain omega-3.
  • Populations in nutrient poor regions might lack iodine and selenium; and certain cultural habits like full body clothing can result in inadequate vitamin D intake in the absence of food or supplement sources.
  • Athletes and heavy exercisers may need a modest increase in some nutrients, but this is usually accounted for by increased calorie intake — as long as the extra food is nutrient dense for the most part.
  • Older people absorb vitamin B12 less well and this may require supplementation. The ill or infirm who do not get adequate sun exposure may require vitamin D supplements.
  • Pre- and during pregnancy, folate supplementation is a useful reassurance against neural tube abnormalities.

However, not only is it likely wasteful to take mega-doses of supplements, it may even be unsafe. The recent scientific examination of vitamin E and beta carotene in high supplement doses has not yielded promise and has suggested adverse effects. If you feel you need to take an individual supplement or a multi, first check out the excellent information at the Office of Dietary Supplements at the NIH. then try not to exceed the RDI by more than a few times for any individual nutrient, unless there are indications that it’s safe and effective to do so.

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