Determinants of Vitamin D Status in Healthy Young Adults from Mexico City.

BACKGROUND AND AIMS: Vitamin D deficiency is a global health problem. The determinants of this deficiency have not been evaluated in developing countries such as Mexico. Thus, this study aimed to determine vitamin D intake and sun exposure and its relationship with plasma concentrations of 25-hydroxyvitamin D -25(OH)D- in young adults from Mexico City. METHODS: One hundred fifty five urban adult subjects were enrolled during 2017 and 2018. Sociodemographic, anthropometric, and clinical data, vitamin D intake, and sun exposure habits were collected. Plasma concentrations of 25(OH)D were also determined. RESULTS: The proportion of vitamin D deficiency was significantly higher in women than in men (65.7 vs. 43.4%, p = 0.012). The overall median dietary vitamin D intake was 112 IU/d (less than 20% of the recommended daily intake; RDI). 25-hydroxyvitamin D correlated directly with vitamin D intake, sun exposure score, waist-to-hip ratio, and age; an inverse significant association was found with body fat percentage. A multiple regression analysis was performed; simultaneous and significant (p <0.01) effects of sun exposure score, dietary vitamin D, the season of the year (spring-summer vs. fall-winter), and age were observed on 25(OH)D levels. CONCLUSION: High rates of vitamin D deficiency and insufficiency were observed in young adults from Mexico City. According to the RDI of this vitamin, its consumption, assessed by a 24 h multi-step nutritional questionnaire, was significantly low. A linear multiple regression model identified several predictors of plasma 25(OH)D concentrations. This multiple regression model was statistically validated.

Vitamin D Receptor Gene Polymorphisms, ß-cell Function, and Vitamin D Status in Non-obese Mexican Adults.

BACKGROUND: FokI (rs2228570 T>C) and BsmI (rs1544410 A>G) polymorphisms of the vitamin D receptor (VDR) have been associated to abnormal glucose metabolism and could be inversely associated with ß-cell function (BCF) and vitamin D status. There is a lack of information about this topic in the Mexican population. AIM OF THE STUDY: To evaluate the relationship between VDR gene polymorphisms FokI and BsmI with BCF and vitamin D status in a population of non-obese Mexican adults. METHODS: A sample of 192 participants were enrolled during 2016-2018. Blood samples were collected to determine fasting concentrations of glucose, insulin, and vitamin D. Genomic DNA was isolated from leucocytes and the polymorphic variants of FokI and BsmI were analyzed. The Homeostasis Model Assessment Calculator was used to estimate the BCF (HOMA2-B). RESULTS: FokI polymorphism showed a frequency of 20.1% for homozygous TT carriers and 7.8% for the BsmI GG. The recessive model of FokI (TT genotype) showed a lower mean value of BCF compared to the combination of CC + CT (99.2 vs. 109.6%, p = 0.045). Likewise, significantly lower mean values of HOMA2-B and insulin were observed for BsmI (GG genotype, p = 0.016 and p = 0.039, respectively). After covariates adjustment, only FokI polymorphism remained as an independent predictor of BCF. CONCLUSIONS: the TT and GG variants of the FokI and BsmI polymorphisms are related to a decrease in FCB. In the case of FokI, this decrement was independent of insulin sensitivity, vitamin D levels, percentage of body fat, gender, and age.

Optimal Cut-off Points of Fasting and Post-Glucose Stimulus Surrogates of Insulin Resistance as Predictors of Metabolic Syndrome in Adolescents According to Several Definitions

OBJECTIVE: The aim of this study was to determine optimal cut-off points for fasting and post-glucose stimulus surrogates of insulin resistance to predict metabolic syndrome in adolescents according to several definitions. METHODS: One hundred fifty-five adolescents living in Mexico City were enrolled during 2011 and 2012. Waist circumference and blood pressure were recorded. Subjects received an oral glucose load of 1.75 g per kg up to a maximum dose of 75 g. Blood samples were drawn at baseline and 120 minutes. Concentrations of plasma glucose, triglycerides, high-density lipoprotein cholesterol and insulin were determined. RESULTS: The frequency of metabolic syndrome showed a large variability when using a variety of published definitions; in contrast, the optimal cut-off points for fasting insulin, homeostatic model assessment of insulin resistance and two-hour oral glucose tolerance test insulin were very similar in almost all the definitions considered and had adequate diagnostic performance: area under the curve >0.869, sensitivity >0.835 and specificity >0.755. Insulin resistance surrogates had substantial agreements with Ford, Cook and Salas definitions (Kappa~0.62; agreement~82%); moderate agreement was observed for International Diabetes Federation, Cruz and Ferranti definitions (Kappa~0.41­0.59; agreement~77%). CONCLUSION: Insulin resistance surrogates may be a better approach for metabolic syndrome assessment in an adolescent population because of reduced variability and a higher predictive value.