Effects of Vitamin D Supplementation on Insulin Sensitivity and Secretion in Prediabetes.

CONTEXT: Vitamin D regulates glucose homeostasis pathways, but effects of vitamin D supplementation on ß-cell function remain unclear. OBJECTIVE: To investigate the effects of vitamin D3 supplementation on insulin sensitivity and ß-cell function. METHODS: This is a prespecified secondary analysis of the Vitamin D and Type 2 Diabetes study. Overweight/obese adults at high risk for type 2 diabetes (prediabetes) were randomly treated with vitamin D3 4000 IU or matching placebo daily for 24 months. MAIN OUTCOME: Disposition index (DI), as an estimate of ß-cell function, was calculated as the product of Homeostasis Model Assessment 2 indices derived from C-peptide values (HOMA2%Scpep) and C-peptide response during the first 30 minutes of a 75-g oral glucose tolerance test (OGTT). RESULTS: Mean age was 60.5 ± 9.8 years and body mass index was 31.9 ± 4.4 kg/m2. Mean serum 25(OH)D level increased from 27.9 ± 10.3 ng/mL at baseline to 54.9 ng/mL at 2 years in the vitamin D group and was unchanged (28.5 ± 10.0 ng/mL) in the placebo group. The baseline DI predicted incident diabetes independent of the intervention. In the entire cohort, there were no significant differences in changes in DI, HOMA2%Scpep, or C-peptide response between the 2 groups. Among participants with baseline 25(OH)D level <12 ng/mL, the mean percent differences for DI between the vitamin D and placebo groups was 8.5 (95% CI, 0.2-16.8). CONCLUSIONS: Supplementation with vitamin D3 for 24 months did not improve an OGTT-derived index of ß-cell function in people with prediabetes not selected based on baseline vitamin D status; however, there was benefit among those with very low baseline vitamin D status.

Effect of Vitamin D Supplementation on Kidney Function in Adults with Prediabetes: A Secondary Analysis of a Randomized Trial.

BACKGROUND AND OBJECTIVES: Low serum 25-hydroxyvitamin D (25[OH]D) concentration has been associated with higher levels of proteinuria and lower levels of eGFR in observational studies. In the Vitamin D and Type 2 Diabetes (D2d) study, we investigated the effect of vitamin D supplementation on kidney outcomes in a population with prediabetes. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Overweight/obese adults with high risk for type 2 diabetes (defined by meeting two of three glycemic criteria for prediabetes) were randomized to vitamin D3 4000 IU per day versus placebo. Median duration of treatment was 2.9 years (interquartile range 2.0-3.5 years). Kidney outcomes included (1) worsening in Kidney Disease: Improving Global Outcomes (KDIGO ) risk score (low, moderate, high, very high) on two consecutive follow-up visits after the baseline visit and (2) mean changes in eGFR and urine albumin-to-creatinine ratio (UACR). RESULTS: Among 2166 participants (mean age 60 years, body mass index 32 kg/m2, serum 25(OH)D 28 ng/ml, eGFR 87 ml/min per 1.73 m2, UACR 11 mg/g, 79% with hypertension), 10% had moderate, high, or very high KDIGO risk score. Over a median follow-up of 2.9 years, there were 28 cases of KDIGO worsening in the vitamin D group and 30 in the placebo group (hazard ratio, 0.89; 95% confidence interval [95% CI], 0.52 to 1.52]). Mean difference in eGFR from baseline was -1.0 ml/min per 1.73 m2 (95% CI, -1.3 to -0.7) in the vitamin D group and -0.1 ml/min per 1.73 m2 (95% CI, -0.4 to 0.2) in the placebo group; between-group difference was -1.0 ml/min per 1.73 m2 (95% CI, -1.4 to -0.6). Mean difference in UACR was 2.7 mg/g (95% CI, 1.2 to 4.3) in the vitamin D group and 2.0 (95% CI, 0.5 to 3.6) in the placebo group; between-group difference was 0.7 mg/g (95% CI, -1.5 to 2.9). CONCLUSIONS: Among persons with prediabetes, who were not preselected on the basis of serum 25(OH)D concentration, vitamin D supplementation did not affect progression of KDIGO risk scores and did not have a meaningful effect on change in UACR or eGFR.

Establishing an electronic health record-supported approach for outreach to and recruitment of persons at high risk of type 2 diabetes in clinical trials: The vitamin D and type 2 diabetes (D2d) study experience.

AIMS: To establish recruitment approaches that leverage electronic health records in multicenter prediabetes/diabetes clinical trials and compare recruitment outcomes between electronic health record-supported and conventional recruitment methods. METHODS: Observational analysis of recruitment approaches in the vitamin D and type 2 diabetes (D2d) study, a multicenter trial in participants with prediabetes. Outcomes were adoption of electronic health record-supported recruitment approaches by sites, number of participants screened, recruitment performance (proportion screened who were randomized), and characteristics of participants from electronic health record-supported versus non-electronic health record methods. RESULTS: In total, 2423 participants were randomized: 1920 from electronic health record (mean age of 60 years, 41% women, 68% White) and 503 from non-electronic health record sources (mean age of 56.9 years, 58% women, 61% White). Electronic health record-supported recruitment was adopted by 21 of 22 sites. Electronic health record-supported recruitment was associated with more participants screened versus non-electronic health record methods (4969 vs 2166 participants screened), higher performance (38.6% vs 22.7%), and more randomizations (1918 vs 505). Participants recruited via electronic health record were older, included fewer women and minorities, and reported higher use of dietary supplements. Electronic health record-supported recruitment was incorporated in diverse clinical environments, engaging clinicians either at the individual or the healthcare system level. CONCLUSION: Establishing electronic health record-supported recruitment approaches across a multicenter prediabetes/diabetes trial is feasible and can be adopted by diverse clinical environments.

Baseline Characteristics of the Vitamin D and Type 2 Diabetes (D2d) Study: A Contemporary Prediabetes Cohort That Will Inform Diabetes Prevention Efforts.

OBJECTIVE: To describe baseline characteristics of the Vitamin D and Type 2 Diabetes (D2d) study, the first large U.S. diabetes prevention clinical trial to apply current American Diabetes Association (ADA) criteria for prediabetes. RESEARCH DESIGN AND METHODS: This is a multicenter (n = 22 sites), randomized, double-blind, placebo-controlled, primary prevention clinical trial testing effects of oral daily 4,000 IU cholecalciferol (D3) compared with placebo on incident diabetes in U.S. adults at risk for diabetes. Eligible participants were at risk for diabetes, defined as not meeting criteria for diabetes but meeting at least two 2010 ADA glycemic criteria for prediabetes: fasting plasma glucose (FPG) 100-125 mg/dL, 2-h postload glucose (2hPG) after a 75-g oral glucose load 140-199 mg/dL, and/or a hemoglobin A1c (HbA1c) 5.7-6.4% (39-46 mmol/mol). RESULTS: A total of 2,423 participants (45% of whom were women and 33% nonwhite) were randomized to cholecalciferol or placebo. Mean (SD) age was 59 (9.9) years and BMI 32 (4.5) kg/m2. Thirty-five percent met all three prediabetes criteria, 49% met the FPG/HbA1c criteria only, 9.5% met the 2hPG/FPG criteria only, and 6.3% met the 2hPG/HbA1c criteria only. Black participants had the highest mean HbA1c and lowest FPG concentration compared with white, Asian, and other races (P < 0.01); 2hPG concentration did not differ among racial groups. When compared with previous prediabetes cohorts, the D2d cohort had lower mean 2hPG concentration but similar HbA1c and FPG concentrations. CONCLUSIONS: D2d will establish whether vitamin D supplementation lowers risk of diabetes and will inform about the natural history of prediabetes per contemporary ADA criteria.

The assessment of diabetes knowledge and self-efficacy in a diverse population using Rasch measurement.

The purpose of this research was to develop survey instruments to evaluate diabetes knowledge and self-efficacy in a diverse population, and investigate the psychometric properties of data obtained with these instruments using Rasch measurement. Two-hundred and fifty-five urban-dwelling participants with diabetes were recruited to complete surveys through independent interviews. To evaluate the association of health literacy on metabolic control, formal literacy and hemoglobin A1c fingerstick testing were performed. Rasch analysis of the data yielded item and person calibrations for self-efficacy and knowledge, with variable maps created to provide both norm and criterion-referenced interpretations. Knowledge scale person separation reliability was 0.50 and item separation reliability was 0.98; while self-efficacy scale person separation reliability was 0.72 with item separation reliability of 0.92. Statistically significant partial correlations were observed between knowledge and health literacy (r = 0.41, p<.001), and self-efficacy and hemoglobin A1c (r = -0.33, p<.001). However, there was no correlation between diabetes knowledge and hemoglobin A1c (r = 0.035, p = 0.29), or health literacy and A1c (r = 0.022, p = 0.36). Diabetes knowledge varied, with non-English speaking individuals having lower measures than English speakers (t(252) = -4.86, p<.001). Non-English speaking individuals also had lower self-efficacy measures than English speakers (t(251) = -2.68, p = .008). Current knowledge deficits and perceptions of self-management may be estimated visually through variable mapping, which may help in individualizing informational needs for people with diabetes.

Implementation and evaluation of a low-literacy diabetes education computer multimedia application.

OBJECTIVE: To evaluate a clinic-based multimedia intervention for diabetes education targeting individuals with low health literacy levels in a diverse population. RESEARCH DESIGN AND METHODS: Five public clinics in Chicago, Illinois, participated in the study with computer kiosks installed in waiting room areas. Two hundred forty-four subjects with diabetes were randomized to receive either supplemental computer multimedia use (intervention) or standard of care only (control). The intervention includes audio/video sequences to communicate information, provide psychological support, and promote diabetes self-management skills without extensive text or complex navigation. HbA(1c) (A1C), BMI, blood pressure, diabetes knowledge, self-efficacy, self-reported medical care, and perceived susceptibility of complications were evaluated at baseline and 1 year. Computer usage patterns and implementation barriers were also examined. RESULTS: Complete 1-year data were available for 183 subjects (75%). Overall, there were no significant differences in change in A1C, weight, blood pressure, knowledge, self-efficacy, or self-reported medical care between intervention and control groups. However, there was an increase in perceived susceptibility to diabetes complications in the intervention group. This effect was greatest among subjects with lower health literacy. Within the intervention group, time spent on the computer was greater for subjects with higher health literacy. CONCLUSIONS: Access to multimedia lessons resulted in an increase in perceived susceptibility to diabetes complications, particularly in subjects with lower health literacy. Despite measures to improve informational access for individuals with lower health literacy, there was relatively less use of the computer among these participants.

Proteasome production in human muscle during nutritional inhibition of myofibrillar protein degradation.

Protein undernutrition inhibits adenosine triphosphate (ATP)-dependent muscle protein degradation-a hallmark of the proteasome system. Here we report decreased myofibrillar protein degradation during dietary protein restriction without a concomitant decrease in proteasome gene expression, proteasome protein abundance, or proteasome in vivo fractional synthesis rate. Healthy human subjects consuming the average minimum adult protein requirement (0.71 g x kg(-1) fat-free mass x d(-1)) exhibited substantially lower (68%) excretion of 3-methylhistidine, an indicator of myofibrillar protein breakdown, when compared with subjects consuming an ample, American-style protein intake (1.67 g x kg(-1) fat-free mass x d(-1)). However, they displayed no difference in the expression of mRNA for proteasome subunits C2 or C3, in the content of C2 protein, or in the rate of incorporation of stable isotopically labeled l-[1-(13)C]-leucine into proteasome proteins. The results demonstrate that nutritional inhibition of myofibrillar protein degradation does not involve suppression in vivo of proteasome production in man. This suggests that other elements of the ubiquitin-proteasome system, such as ubiquitination pathways, are more important than proteasome abundance in the nutritional regulation of skeletal muscle mass.

Isoenergetic dietary protein restriction decreases myosin heavy chain IIx fraction and myosin heavy chain production in humans.

The synthesis of muscle protein is restrained during dietary protein restriction. This is widely understood to vary quantitatively with the degree of nutritional deprivation, but there has been little discussion of qualitative changes in muscle protein deriving from dietary protein restriction. We studied 14 healthy subjects in a 2-sample study. Subjects were randomly assigned to a diet providing an ample, American-style protein intake (1.67 g. kg fat-free mass(-1). d(-1)) or a diet approximating the mean minimum adult protein requirement (0.71 g. kg fat-free mass(-1). d(-1)). We found that consumption of an isoenergetic diet at the mean adult minimum protein requirement for 4 wk produced an 81% lower fractional synthesis rate of myosin heavy chain (MHC) proteins in vastus lateralis muscle than did consumption of an ample protein diet (P = 0.05). Protein deprivation altered the skeletal muscle myosin composition such that the proportion of the total myosin content represented by fast-twitch MHC IIx was 51% lower than with ample intake (P = 0.013). The steady state content of MHC IIx messenger RNA (mRNA) did not differ in subjects consuming the minimum requirement of protein, suggesting that the reduced proportion of MHC IIx arises from posttranscriptional events. A 68% lower rate of 3-methylhistidine excretion with protein restriction (P < 0.01) suggests that myofibrillar protein degradation was lower. We conclude that dietary amino acid scarcity produces a change in myosin isoform distribution via posttranscriptional mechanisms. The relative contribution of inhibited myosin synthesis and inhibited degradation to the altered myosin isoform composition remains unknown. This has implications for the mechanisms by which amino acids govern muscle protein composition in vivo, and further exploration is required.

Modulation of the ubiquitin-proteasome proteolytic pathway by eicosapentaenoic acid supplementation in a model of progressive malignancy.

BACKGROUND: A benefit for eicosapentaenoic acid (EPA) supplementation for protein maintenance in cancer patients exists, although specific mechanisms are unknown. As the ubiquitin-proteasome proteolytic (UPP) pathway has been implicated in protein use in malignancy, we determined mRNA levels for UPP components in the liver and muscles from EPA-treated rats bearing the methylcholanthrene (MCA) fibrosarcoma. METHODS: Rats implanted with MCA tumor were divided into 3 groups on day 13: EPA (5 g/kg per day plus 10 IU vitamin E/g fat), corn oil (5 g/kg per day plus 10 IU vitamin E/g fat), and saline (5 g/kg per day plus 10 IU E/g saline). On day 29, tumor volume (TV) was determined; liver and quadriceps muscles were also excised to determine gene expression of C2, C3, E2(14k), and E3alpha by reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: EPA-treated rats demonstrated a reduced TV of 21% compared with the 28% and 30% TV of corn oil- and saline-treated rats, respectively. Muscle mRNA levels of E2(14k) and E3alpha in EPA-treated animals were decreased compared with corn oil- and saline-treated animals. EPA treatment also decreased hepatic C2, C3, and E2(14k) mRNA levels compared with saline treatment. CONCLUSION: EPA supplement decreased skeletal muscle E2(14k), E3alpha, and hepatic C2 mRNA levels compared with the isocaloric, isonitrogenous corn oil supplement, supporting a treatment-specific effect. The decrease in hepatic C3 and E2(14k) mRNA levels induced by EPA were partly because of caloric benefit and partly attributable to a treatment-specific effect. Additionally, differences in the hepatic and muscle gene expressions of UPP components suggested an organ-specific effect for omega-3 fatty acid activity.