Date: 20 Aug 1994 07:48:29 -0700
From: taltar@vertigo.helix.net (Ted Altar)
Subject: Historic Trend of RDAs (repost)
Newsgroups: rec.food.veg
Organization: Helix Internet
Lines: 53

RDA'S ARE GENERALLY CHANGING DOWNWARD

Some would think that a nation's RDA's are written in stone,
or that at the very least they have been changing upwards.
In fact, they are not.  That they do change over time as new
and more accurate knowledge is obtained should come as no
surprise, yet even this fact is not well appreciated by even
the most nutritionally informed.

For example, here is the actual table regarding the history
of U.S.A. RDA's for males 25-50, as put out by the U.S. NRC.

                         RDA Changes over the last 50 years
VITAMIN          '41    '48    '57    '68     '76      '80     89
---------------------------------------------------------------------
A (mg           1000   1000   1000   1000    1000     1000    1000
D                                     400IU   400IU      5ug     5ug
E (ug)                                 30      15       10      10
K (mg)                                                          80
C (mg)            75     75     70     60      45       60      60
Thiamin (mg)       2.3    1.5     .9    1.3     1.4      1.4     1.5
Riboflavin (mg)    3.3    1.8    1.3    1.7     1.6      1.6     1.7
Niacin (mg)       23     15     15     17      18       18      19
B6 (mg)                                 2.0     2.0      2.2     2.0
Folate (ug)                           400     400      400     200
B12 (ug                                 3       3        5       2

Over all, the general historical trend for adults would appear
to be downward, not upward!  This is what we might expect as more
accurate information is obtained clarifying former areas of uncertainty
that resulted in margins of safety greater than what was actually
required.

Given this information, it would seem more useful to simply talk
about specific vitamins being increased, should this be the case,
with respect to an immediately preceding RDA guideline, and maybe
with respect to certain age-sex groupings.

With respect to the historical trend for RDAs in general,
Gerald Combs (1992, p. 480) himself says,

     "As available information bases improve, expert committees
     typically have REDUCED the levels of their recommendations
     for nutrient allowances.  This likely reflects a basically
     conservative nature of the committee system used for these
     purposes, whereby the paucity of data tends to be handled
     by generously estimating quantitative needs."

					Regards,
						Ted
		"You are what you do, and that includes eating"  ;-)