What about Recommended Dietary Allowances?

In an effort to answer the question of how much people should aim to eat of the major nutrients, recommended dietary allowances (RDAs) were established by the Food and Nutrition Board of the US National Academy of Sciences National Research Council. RDAs were originally developed in the 1940s for food production in the military, and since their publication in 1943, they have been recognized as the most authoritative source of information on nutrient levels for healthy people. They are regularly updated, and since publication of the 10th edition in 1989, there has been an enormous amount of new research on the impact of nutrition on chronic disease.

In order to try and take this research into account, the expert panel responsible for setting the RDAs has reviewed and revised its approach and have published a new set of guidelines known as the Dietary References Intakes (DRI).

This new series of references includes what is known about how the nutrient functions in the human body; which factors may affect how it works; and how the nutrient may be related to chronic disease. Scientific research on nutrient metabolism and data on intakes in the US population, are used to set intakes for each age group, from babies to elderly people. Recommendations for pregnancy, lactation and maximum intake are also made.

The DRI provides sets of measures for each nutrient. The first of these is the Estimated Average Requirement (EAR), the intake value that is estimated to meet the requirement in 50 per cent of people in a specific group, usually defined by age and sex. At this level of intake, the remaining 50 per cent of the group would not have its needs met. The Recommended Dietary Allowance (RDA) is the dietary intake level that is sufficient to meet the nutrient requirements of nearly all the people in the group. These values refer to average daily intake over one or more weeks. The Tolerable Upper Intake Level (UL) is the upper limit of intake associated with a low risk of adverse effects in most people. It applies to long-term daily use.

For some essential vitamins and minerals, there is not enough information to come up with RDAs; and even for those nutrients for which they have been established, the lack of enough basic data means that they may be less accurate than they ideally should be. Where the experts consider that there is not enough evidence to come up with RDAs, they have established adequate intake (AI) values. DRIs have been published for the B vitamins, calcium, phosphorus, vitamin D, fluoride and magnesium. Others will follow in the near future. RDAs are designed for those of average height, weight, nutrient absorption ability and stress levels; and those who do not fit into those categories may need more. RDAs contain a margin of safety to make allowances for individual differences in absorption and metabolism. The RDA can be used as a goal for planning individual dietary intake. It is not intended to be used for assessing the diets of either individuals or groups or for planning diets for groups. The EAR may be more suitable for that purpose.

A separate set of recommendations called Reference Daily Intakes (RDIs) (previously known as the US RDAs) has been developed by the Food and Drug Administration (FDA). These do not vary with age or gender, but take the highest recommended dietary allowance value. On food labels you may see these referred to as Daily Values (DVs), listed for people who eat 2000 to 2500 calories each day.

Other countries use slightly different terms to refer to the RDAs. In Australia, the term Recommended Dietary Intakes (RDI) is used and in the UK, Recommended Nutrient Intakes (RNI).

UK, Recommended Nutrient Intakes (RNI). The RDIs set by the FDA are:

Vitamin A 5,000 iu
Vitamin C 60 mg
Vitamin D 400 IU
Vitamin E 30 IU
Vitamin K 80 mcg
Thiamin (B-1) 1.5 mg
Riboflavin (B-2) 1.7 mg
Niacin (B-3) 20 mg
Vitamin (B-6) 2 mg
Folate 400 mcg
Vitamin B-12 6 mcg
Biotin 300 mcg
Pantothenic Acid (B-5) 10 mg
Calcium 1,000 mg
Magnesium 400 mg
Phosphorous 1,000 mg
Chloride 3,400 mg
Chromium 120 mcg
Copper 2 mg
Iodine 150 mcg
Iron 18 mg
Manganese 2 mg
Molybdenum 75 mcg
Selenium 70 mcg
Zinc 15 mg

RDAs can be used as a basis for planning daily intakes. Many nutritionists advise aiming for 100 per cent of the RDA for all nutrients including vitamins and minerals. Greater intakes of vitamin C, beta carotene (which the body can convert to vitamin A) and vitamin E might be beneficial; but intakes of vitamins and minerals which may be toxic in large doses, such as vitamin A and vitamin D, should be limited to no more than 300 per cent of the RDA.

RDAs are calculated to meet the needs of healthy people, rather than the needs of those who are ill, stressed, taking medications or living in environments which cause nutrient requirements to be raised. They are also designed for people who are not particularly active, and those who exercise a lot may have greater needs. In recognition of the fact that older people usually require much higher levels of nutrients than those covered by the old RDAs, the new DRIs are, in some cases, higher for older people.

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