Recommended Dietary Allowances (RDAs)

For many years the National Research Council of the United States National Academy of Sciences has taken responsibility for establishing guidelines on what quantities of the various nutrients should be eaten by human males and females at various ages. These were called RDAs (for Recommended Dietary Allowances, and often referred to as Recommended Daily Allowances).

However, on August 13, 1997, the Institute of Medicine of the National Academy published a report that:

set new standards for calcium intake (as well as for Vitamin D, fluoride, magnesium, and phosphorus)
dropped the name RDA in favor of Dietary Reference Intakes (DRIs)
added three new categories:
- adequate intake ("AI"), where no RDA has been established
- estimated safe and adequate daily dietary intake ("ESADDI"), expected to satisfy the needs of 50% of the people in that age group)
- tolerable upper intake levels ("UL"), to caution against excess intake of nutrients - like vitamin D - that can be harmful in large amounts.

As their findings trickle in, here is a table of RDAs (or AIs) for young adult women and men.

	Females	Males		Females	Males
Protein	46 g	56 g	Folacin	400 µg	same
Vitamin A (retinol)	700 µg*	900 µg*	Biotin	30 µg (AI)	same
Thiamine (Vitamin B₁)	1.1 mg	1.2 mg	Calcium	1000 mg (AI)	same
Riboflavin (Vitamin B₂)	1.1 mg	1.3 mg	Phosphorus	700 mg	same
Niacin (Vitamin B₃)	14 mg	16 mg	Selenium	55 µg	same
Pantothenic acid (Vitamin B₅)	5 mg (AI)	same	Iron	18 mg	8 mg
Vitamin B₆	1.3 mg	same	Zinc	8 mg	11 mg
Vitamin B₁₂	2.4 µg	same	Magnesium	310 mg	400 mg
Vitamin C	75 mg*	90 mg*	Iodine	150 µg	same
Vitamin D	5 µg (AI)**	same	Fluoride	3 mg (AI)	4 mg (AI)
Vitamin E	15 mg**	same	Linoleic acid	12 g (AI)	17 g (AI)
Vitamin K	90 µg (AI)	120 µg	α-Linolenic acid	1.1 g (AI)	1.6 g (AI)

*This value has recently been questioned following the publication of data indicating that a high intake of retinol in older people leads to an increased risk of hip fractures. Vitamin A stimulates osteoclasts, the cells that degrade bone, and inhibits osteoblasts, the cells that build bone. To the extent that the vitamin A requirement is met by ingested beta-carotene, these amounts should be multiplied by 12. And that is probably the best way to get your vitamin A as the body only converts enough beta-carotene into vitamin A to meet its needs. In short, probably no one should consume vitamin tablets containing vitamin A (those with beta-carotene are fine).
*Smokers should add 35 mg to these values.
**5 µg = 200 IU ("International Units").
**The upper limit (UL) is 1,000 mg/day.

Some nutritionists think that the allowances for vitamins C and D are too low.

A study published in April 1996 suggests that 200 mg of Vitamin C per day is probably optimal. This is more than twice the current RDA, but far lower than the 2,000 mg/day that is the UL and that some people exceed in the hope of warding off colds, cancer, etc. Furthermore, an in vitro study reported in the 15 June 2001 issue of Science found that a level of vitamin C equivalent to a person consuming only 200 mg a day converts some body lipids into substances that can damage DNA.
The National Institute of Medicine has now established the following AIs for vitamin D:
- 5 µg (200 IU) for adults from age 20 to 50
- 10 µg (400 IU) for those between 50 and 70
- 15 µg (600 IU) for those over 70 years of age
However, a study reported in the 19 March 1998 issue of The New England Journal of Medicine indicates that perhaps all adults should receive 20 to 25 µg (800 - 1000 IU) of vitamin D per day.

There is also evidence that beta-carotene has important functions besides being the precursor of vitamin A and therefore should be ingested in amounts greater than needed to meet the vitamin A requirement. In fact, this is probably the best way to secure a safe amount of vitamin A. Several studies have shown that in affluent countries, ingesting vitamin A from vitamin supplements and fortified food in amounts that are even slightly above the RDA lead to an increased risk of bone fractures later in life.

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1 July 2009