Mediators of the Effect of Childhood Socioeconomic Status on Late Midlife Cognitive Abilities: A Four Decade Longitudinal Study

Background and Objectives

Childhood socioeconomic status (cSES) is found to predict later-life cognitive abilities, yet the mechanisms underlying these associations remain unclear. The objective of this longitudinal study was to examine the direct and indirect paths through which cSES influences late midlife cognitive outcomes.

Research Design and Methods

Participants were 1,009 male twins in the Vietnam Era Twin Study of Aging (VETSA). At mean ages 20 and 62, participants completed a standardized test for general cognitive ability (GCA). The age 62 cognitive assessment also included in-person tests of processing speed, episodic memory, abstract reasoning, working memory, verbal fluency, visual-spatial ability, and executive functions. At mean age 56, participants were interviewed regarding their own and their parents’ education and occupation, and completed questionnaires about cognitive leisure activities and sociodemographic information. Multiple mediation analyses were conducted to examine the direct path effects and indirect path effects of cSES through age 20 GCA, adult SES, and cognitive leisure activities on seven cognitive outcomes at age 62, adjusting for age, ethnicity, and non-independence of observations.

Results

Total (direct plus indirect) effects were significant for all measures with the exception of executive functions. Men from lower cSES backgrounds had poorer cognitive functioning in late midlife. The direct effect of cSES was partially mediated for abstract reasoning, and was fully mediated for the remaining six cognitive outcomes. Total indirect effects accounted for at least half of the total effects in each model, with paths through age 20 GCA explaining most of the total indirect effects.

Discussion and Implications

cSES predicted cognitive functioning in late middle age Using multiple mediation models, we show that lower cSES predicts poorer cognition in late midlife primarily through young adult cognitive ability and to a lesser extent through SES in adulthood and engagement in cognitively stimulating activities.

The oxidation and decarboxylation of retinoic acid by horseradish peroxidase

The decarboxylation of retinoic acid by horseradish peroxidase was investigated. A marked increase in the yield of products was obtained. However, the data indicated the reaction was a nonenzymatic, heme catalyzed peroxidation. Previously reported requirements for phosphate, oxygen and ferrous ion were eliminated when hydrogen peroxide was provided. Peroxide also eliminated the EDTA and cyanide induced inhibition of the phosphate dependent system. In the presence of hydrogen peroxide, horseradish peroxidase was not essential to the reaction; heme equivalent amounts of hemoglobin decarboxylated retinoic acid with equal facility. However, hemoglobin was ineffective in the absence of hydrogen peroxide. Attainment of 50--60% decarboxylation represented complete utilization of the available retinoic acid. Thus the products of the reaction can be divided into two groups, products of retinoic acid oxidation and products of an oxidative decarboxylation of retinoic acid.

Isolation and partial characterization of rate casein proteins

Casein was isolated from rat milk by high speed centrifugation. Polyacrylamide disc gel electrophoresis of the whole casein yielded three major protein zones designated C.1, C.2, and C.3 in order of their decreasing electrophoretic mobility in the alkaline system. Zone 3 subsequently contained two possibly related bands, C.3.1 and C.3.2. The presence of phosphate in all four zones was indicated by staining and conformed by phosphorus-32 labeling studies. A glycoprotein character was indicated by all zones. Separation of the constituents of rat casein by diethylaminoethyl-cellulose ion exchange chromatography yielded the same four major protein entities. Three milk-specific phosphoproteins unique to rat whey cluted from such columns in the same general region as the casein constituents but appear to be otherwise unrelated to the four major components of micellar casein. Gel electrophoresis in sodium dodecyl sulfate systems yielded apparent molecular weight estimates of approximately 24,000 for C.1, 38,000 for C.2, and 28,000 for c.3.1 and c.3.2.

Purification and partial characterization of a unique group of phosphoproteins from rat milk whey

A group of four electrophoretically distinct but related proteins has been isolated from rat milk whey. These have been classified as P.1 to P.4 in order of their decreasing electrophoretic mobility in an alkaline buffer system. All four members of this group of proteins are immunologically identical apparently constitute a single protein which is differentially phosphorylated in the ratio of 3:2:1:0. Sodium dodecyl sulfate gel electrophoresis yielded constant estimates of molecular weight of approximately 20,700. Enzymatic dephosphorylation of purified P.1 generated the other three members of the group, demonstrating the commonality of the peptide component. This group of proteins in total makes a significant contribution of the total whey proteins being approximately 5 mg/ml in whole rat milk in the approximate proportion of 1:1.5:2:1.5. The P.1, P.2, and P.3 were isolated in sufficient quantities to permit further characterization. The partial amino acid analyses of each of the three forms were similar. They had commonextinction coefficients, E1(1)% cm A280, of 4.9 and A280/A290 ratio of about 1.36.

Purification and characterization of rat alpha-lactalbumins: apparent genetic variants

Rat alpha-lactalbumin, from the milk of Fischer 344 (CDF) rats, was isolated and purified by a combination of gel filtration and diethylaminoethyl-cellulose ion exchange chromatography. Three electrophoretically distinct proteins had alpha-lactalbumin activity. Staining for carbohydrate indicated that at least two of the three forms were glycoproteins. The low molecular weight protein fraction from the wheys of two additional strains of laboratory rat were compared to ascertain whether the composition of this fraction was common in the divergent strains. Outbred Wistar and Long-Evans dams yielded wheys containing up to six forms of alpha-lactalbumin. Either one or both of two groups of three alpha-lactalbumins were in a given milk sample. The two groups of three alpha-lactalbumins appear to represent two genetic variants upon which is imposed a polymorphic character. All forms of alpha-lactalbumin, within and between strains, were immunologically identical.

The relation of laboratory analyses for copper, zinc, and molybdenum in some Victorian soils to the results of field trials

Samples of surface soil from 82 fertilizer trial plots in Victoria were analysed for total copper, zinc, and molybdenum, and for the amounts of these elements extracted by EDTA and normal ammonium acetate, and these values were related to plant responses to fertilizers containing these elements. Predictions of copper deficiency can be made with equal accuracy from a knowledge of the total concentration or from the EDTA soluble copper. For zinc, an approximately equal accuracy of prediction can be made either from the total zinc content and soil reaction or from the EDTA soluble zinc and soil reaction. There was no relation between total or extractable molybdenum and deficiency. The amounts of copper and zinc, but not molybdenum, extracted by both extractants were correlated with the total concentrations in the soil. (r = 0.80 for EDTA Cu, 0.76 for ammonium acetate Cu, 0.47 for EDTA Zn, and 0.32 for ammonium acetate Zn.) The total concentrations of copper and zinc were also correlated with the nitrogen content of the soil (r = 0.38 for Cu, 0.42 for Zn), as were the amounts of copper (r = 0.46), zinc (r = 0.42), and molybdenum (r = 0.43) extracted by EDTA, and the amounts of copper (r = 0.36) and molybdenum (r = 0.40) extracted by ammonium acetate.

Trace elements in some South Australian terra rossa and rendzina soils

The concentrations of cobalt, zirconium, nickel, copper, vanadium, molybdenrun, manganese, and zinc have been determined in 10 profiles of terra rossas and 9 of rendzinas from South Australia. The soils from the lower south-eastern part of the State contain lower concentrations of all these elements than do those near Adelaide, particularly for cobalt, copper, and zinc. This difference is reflected in the concentrations found in the underlying calcareous material, and can account for the widespread deficiencies in cobalt and copper which occur ill the South-East.

The distribution of trace elements in some South Australian red-brown earths

The maximum, minimum, and mean values for six trace elements in four soil horizons are reported for 14 profiles of red-brown earths from South Australia, and the pattern of variation and distribution of these elements discussed. The elements studied could be arranged in a series of decreasing mobility in the soil, the order being cobalt > copper > gallium > vanadium > molybdenum > manganese. The most mobile elements had greater variations within profiles and, except for manganese, greater variations between profiles. Gallium, vanadium, and molybdenum contents were correlated with the amount of clay present in all surface soils, as well as in individual profiles, whereas cobalt and copper contents were correlated with clay only in individual profiles.