Dietary Protein Sources, Mediating Biomarkers, and Incidence of Type 2 Diabetes: Findings From the Women's Health Initiative and the UK Biobank

OBJECTIVE

Whether and how dietary protein intake is linked to type 2 diabetes (T2D) remains unclear. The aim of this study was to investigate the associations of protein intake with development of T2D and the potential mediating roles of T2D biomarkers.

RESEARCH DESIGN AND METHODS

We included 108,681 postmenopausal women without T2D at baseline from the Women's Health Initiative (WHI) (primary cohort) and 34,616 adults without T2D from the U.K. Biobank (UKB) (replication cohort). Cox proportional hazard models were used for estimation of protein-T2D associations. Mediation analysis was performed to assess the mediating roles of biomarkers in case-control studies nested in the WHI.

RESULTS

In the WHI, 15,842 incident T2D cases were identified during a median follow-up of 15.8 years. Intake of animal protein was associated with increased T2D risk (hazard ratio in comparing the highest to the lowest quintile = 1.31 [95% CI 1.24-1.37]) and plant protein with decreased risk (0.82 [0.78-0.86]). Intakes of red meat, processed meat, poultry, and eggs were associated with increased T2D risk and whole grains with decreased risk. Findings from the UKB were similar. These findings were materially attenuated after additional adjustment for BMI. Substituting 5% energy from plant protein for animal protein was associated with 21% decreased T2D risk (0.79 [0.74-0.84]), which was mediated by levels of hs-CRP, interleukin-6, leptin, and SHBG.

CONCLUSIONS

Findings from these two large prospective cohorts support the notion that substituting plant protein for animal protein may decrease T2D risk mainly by reducing obesity-related inflammation.

Determinants of serum 25-hydroxyvitamin D levels in healthy young adults living in the Western Cape, South Africa

Background: Vitamin D deficiency is fast emerging as a global pandemic. In South Africa few studies have been conducted to determine the vitamin D status of the healthy population.Methods: This prospective study with an analytical component investigated vitamin D status of healthy undergraduate students at two time points (winter and summer) at Stellenbosch University. Serum 25(OH)D was determined, anthropometric measurements taken and dietary vitamin D intake estimated (food-frequency questionnaire). Skin tone was determined (Fitzpatrick skin type classification), and a skin reflectometry device used to measure dermal melanin content.Results: Results of 242 students indicated a mean serum 25(OH)D of 63.80 ± 41.35 ng/ml and a high prevalence of vitamin D sufficiency (88%). Significantly more females experienced suboptimal vitamin D levels than males (18 vs. 5%; p 0.01). Participants with lighter skin tones had higher levels of 25(OH)D than those with darker skin tones (chi-square = 24.02; p = 0.02). The majority (60.74%) had a normal BMI, although there was no significant relationship between BMI and serum 25 (OH)D (Spearman’s r=–0.11; p = 0.09). Total mean dietary vitamin D intake was 7.99 ± 13.81 mcg, with 87.2% having inadequate intake ( 15 mcg). The relationship between total vitamin D intake and serum 25(OH)D was found to be significant in winter (p 0.001) and summer (p = 0.01). Serum vitamin D levels were significantly higher in the winter phase (p 0.001).Conclusions: A low prevalence of vitamin D deficiency was found amongst healthy young adults, despite low dietary vitamin D intakes. Significant relationships were found between serum 25(OH)D and gender, skin tone and vitamin D intake. Further studies need to be conducted, especially in high-risk groups, before results are applied to the greater South African public.

Staff and student health and wellness at the Faculty of Medicine and Health Sciences, Stellenbosch University: current status and needs assessment

Background: Emphasis is currently placed on the importance of employee and student wellness initiatives. The aim was to assess staff and student health status at the Faculty of Medicine and Health Sciences (FMHS), Stellenbosch University (SU), and to conduct a wellness needs assessment.Methods: Online, self-administered questionnaires were used to collect data concerning staff and students. Additionally, students’ anthropometric and biochemical parameters were assessed. Summary statistics, correlation coefficients and appropriate analysis of variance were used for data analyses.Results: Data were obtained from staff (survey: n = 300) and students (screening: n = 536; survey: n = 330). Some 58% (n = 174) of staff had a self-reported BMI of ≥ 25 kg/m2 whilst mean screening values for all variables fell within normal reference ranges for students. In all, 78% (n = 232) of staff reported to exercise 150 min/week and 28% (n = 91) of students were sedentary for 8 h/day; 63% (n = 188) of staff expressed the need to make better food choices, 17% (n = 55) of students were aware of the need to change but experienced reluctance, and both staff and students felt dietary assistance would be beneficial (43% vs. 46%). In addition, 79% of staff (n = 208) and 42% of students (n = 138) reported being under constant pressure.Conclusion: Much can be done to improve the health and well-being of both staff and students at the FMHS, SU. Wellness is a multifactorial concept; as such, health-promotional strategies for classrooms and workplaces should consider all factors in order to provide a holistic approach and potentially identify those who are at risk of a sub-optimal wellness status.

Comparison of students classified as LD who petitioned for or fulfilled the college foreign language requirement

In this study, we compared the cognitive, academic achievement, and demographic profiles of 46 students from one university who had been classified as learning disabled (LD) and had received permission to substitute courses for the university's foreign language (FL) requirement (petition group) with the profiles of 21 students from the same university who had been classified as LD and had fulfilled the university's FL requirement by passing FL courses (nonpetition group). Results showed no significant differences between the two groups on measures of reading, mathematics, written language, American College Testing score, and graduating grade point average when IQ was used as a covariate. More petition than nonpetition students had at least a 1.0 SD discrepancy between IQ and achievement and had been referred only for FL learning problems. More nonpetition than petition students had taken an FL in college and received accommodations in the FL. The two groups together appeared to constitute a heterogeneous group of learners, with more than half failing to meet a minimum discrepancy criterion for classification as LD. The discussion addresses the classification system for LD, the process for determining the presence of FL learning problems and how to address them, and directions for further research.

Students classified as LD and the college foreign language requirement: a quantitative analysis

This study was conducted to determine whether students classified as learning disabled (LD) who were permitted to substitute courses for the college foreign language (FL) requirement at one university would display significant cognitive and academic achievement differences when grouped by level of discrepancy between IQ and achievement, by discrepancy between achievement according to different measures, and by level of performance on phonological-orthographic processing measures, on the Modern Language Aptitude Test (MLAT), and in FL courses. Results showed that there were no differences among students with different levels of discrepancy (i.e., < 1.0 SD, 1.0-1.49 SD, and > 1.50 SD) on MLAT and American College Testing (ACT) scores, graduating grade point average (GPA) or college FL GPA. Results also showed that among students who scored below versus at or above the 25th percentile on phonological-orthographic processing measures, there were no differences on measures of IQ, ACT, MLAT, and GPA, as well as most measures of academic achievement. Implications for the use of the LD label to grant FL course substitutions or waivers, use of the MLAT in the diagnostic and course substitution/waiver process, and the validity and reliability of traditional criteria for the classification as LD are discussed.

Job satisfaction of college graduates with learning disabilities

Job satisfaction, as assessed via five scales that posed questions concerning colleagues, work, supervision, pay, and promotion, as well as overall total job satisfaction, was examined for 55 self-identified college graduates with learning disabilities (LD) and 55 control graduates matched by gender, major, degree, and graduation year. All participants graduated from a competitive midwestern university from 1987 to 1994 and represented advantaged groups when compared to both LD and non-LD populations. The graduates with LD required significantly more time to complete their degrees and showed significantly lower CPAs. Data analysis indicated that the graduates with LD perceived themselves as receiving significantly less pay and promotion opportunities, and reported less total job satisfaction, than graduates without LD. However, no significant salary differences between the groups were found. The implications of these findings are examined.

Gas chromatography-mass spectrometry analysis of vitamin E and its oxidation products

To facilitate studies of vitamin E ( alpha-tocopherol) antioxidant actions in tissues, we have developed a stable isotope dilution capillary gas chromatography-mass spectrometry assay for alpha-tocopherol and its three principal oxidation products, alpha-tocopherolquinone, 5,6-epoxy-alpha-tocopherolquinone, 2, 3-epoxy-alpha-tocopherolquinone, and for alpha-tocopherolhydroquinone, a reduction product of alpha-tocopherolquinone. Deuterium-labeled internal standards (5, 7-[2H3-methyl]-alpha-tocopherol, 2,6-[2H3-methyl]- alpha-tocopherolquinone, 2,6-[2H3-methyl]-5,6-epoxy- alpha-tocopherolquinone, 2,6-[2H3-methyl]-2,3-epoxy- alpha-tocopherolquinone, and 2-[2H3-methyl]- alpha-tocopherolhydroquinone are added to cell or tissue homogenates. The products then are extracted and converted to O-trimethylsilyl derivatives. Products are analyzed by capillary gas chromatography with on-column injection and detected by selected ion monitoring of characteristic fragment ions in electron ionization mode. Standard curves were linear from 25 fmol to 2 pmol for products and from 25 fmol to 4 pmol for alpha-tocopherol. The use of 2H6- and 2H3-internal standards for alpha-tocopherolquinone and alpha-tocopherolhydroquinone permits simultaneous analysis of both products despite possible redox interconversion during sample workup. alpha-Tocopherol oxidized in microsomes treated with azo-bis(amidinopropane HCl) was quantitatively accounted for as the epoxyquinones, alpha-tocopherolquinone, and alpha-tocopherolhydroquinone. However, over half of the oxidation products were present in microsomes as acid-labile tocopherone precursors. This method permits comprehensive assessment of vitamin E status in tissues and quantitative studies of vitamin E antioxidant actions and turnover.

Influence of the CSF bicarbonate concentration on the ventilatory response to CO2 in relation to the location of the central chemoreceptors

In anaesthetized cats, in which the cerebrospinal fluid bicarbonate concentration was varied by a ventriculocisternal perfusion technique, the ventilatory response to CO2 during hyperoxia could be satisfactorily described by VE = S(PCSFCO2 -B). Both the slope S and the intercept B were positively and linearly related to the CSF bicarbonate concentration. Assuming that the PCSFCO2 is equal to the PCO2 in extracellular fluid, it can be shown that VE is a linear, but not a unique function of the [H+] at the site of the chemoreceptors; the slope of this relation varies with the bicarbonate concentration at that site, possibly due to chemical complex formation between HCO-3 and Ca2+ or Mg2+. Changes in the B-value were related to the location of the central chemoreceptors with the models of Pappenheimer and Berndt aand their coworkers. It was found that changes in the CSF bicarbonate concentration are reflected for 60 per cent at the site of the central chemoreceptors, and that this was independent of the cerebral perfusion. Using Berndt's model a distance between CSF and central chemoreceptors of approximately 100 micron was found; this calculated distance is relatively insensitive to relationship (logarithmic or not) between ventilation and H+ concentration and to changes in cerebral perfusion, owing to the approximate nature of the diffusion model.