No abstract

1. Forty-two mothers from social classes I, I1 and IIInon-manual and twenty-one from social classes IIImanual (M), IV and V were studied longitudinally. The mean daily nutrient intakes in months 4-9 of pregnancy, months 2 4 of lactation and 3 and 6 months post-lactation are presented and are compared with the U K and the US recommended daily allowances (RDA).2. The quality of the diets (nutrients per 4184 kJ (1000 kcal)) was found to be better than that of other adult female populations studied in the UK, except for a group of dietitians.3. The mean daily intakes of nutrients for which there are UK RDA were almost all greater than 100% of the RDA. The exceptions were iron, which in the manual group (social classes IIIM, IV and V) was 85% of the RDA in pregnancy and 75% post-lactation, and vitamin D.4. Among the nutrients for which there are US, but not UK RDA, only phosphorus and vitamin B,, intakes were greater than 100% of the RDA in both groups at all stages of the study. Intakes of other nutrients were below the RDA: pantothenate 7G91, vitamin B,, zinc, vitamin E and copper 4G72, folate 2144, and biotin <20% of the RDA.5. The bases of the RDA for adult women were examined; for most nutrients the information is limited. It was concluded that the RDA for magnesium, vitamin E and pantothenate are probably higher than necessary and that deficiency is unlikely; that zinc, copper, vitamin B, and folate are probably 'marginal' nutrients for 'at risk' groups; and that information on biotin is insufficient even roughly to assess the dietary requirement.Recommended daily allowances (RDA) are normally set at levels believed to cover the needs of the majority of the population.. The Department of Health and Social Security (DHSS) (I 979) defines them as 'the amount of the nutrient which should be provided per head in a group of people if the needs of practically all members of the group are to be met', and in the USA the National Research Council (1980) Food and Nutrition Board defines them as 'the level of intake . . . considered . . . adequate to meet the . . . needs of practically all healthy persons'.There are three main bases for establishing RDA: knowledge of the intakes of apparently normal, healthy populations and of populations known to be deficient; knowledge of the amounts required to cure clinical or biochemical signs of deficiency; and studies of metabolism such as measurement of rates of nutrient turnover, or of levels required to maintain metabolic balance or tissue saturation. Such information is used to establish an average requirement for the population, which is then increased by a factor to allow for variability of requirement within that population, and a further factor to allow for inefficient utilization (poor absorption, inefficient conversion of precursors, etc.).The tendency therefore is to set RDA higher rather than lower, and to set them at levels greater than the needs of many individual members of the population. This tendency may be exaggerated when information on which to base estimates o...