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" ;-)