Mediation effect of body mass index on the association between serum magnesium level and insulin resistance in children from Mexico City.

BACKGROUND/OBJECTIVES: Reduced serum magnesium (Mg) levels have been associated with obesity, insulin resistance (IR), type 2 diabetes, and metabolic syndrome in adults. However, in the children population, the evidence is still limited. In this cross-sectional study, we aimed to analyze the association of serum Mg levels with the frequency of overweight and obesity and cardiometabolic traits in 189 schoolchildren (91 girls and 98 boys) between 6 and 12 years old from Mexico City. SUBJECTS/METHODS: Anthropometrical data were collected and biochemical parameters were measured by enzymatic colorimetric assay. Serum Mg level was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The triglyceride-glucose (TyG) index was used as a surrogate marker to evaluate IR. RESULTS: Serum Mg level was negatively associated with overweight (Odds ratio [OR] = 0.377, 95% confidence interval [CI] 0.231-0.614, p < 0.001) and obesity (OR = 0.345, 95% CI 0.202-0.589, p < 0.001). Serum Mg level resulted negatively associated with body mass index (BMI, ß = -1.16 ± 0.26, p < 0.001), BMI z-score (ß = -0.48 ± 0.10, p < 0.001) and TyG index (ß = -0.04 ± 0.04, p = 0.041). Through a mediation analysis was estimated that BMI z-score accounts for 60.5% of the negative association of serum Mg level with IR (Sobel test: z = 2.761; p = 0.005). CONCLUSION: Our results evidence that BMI z-score mediate part of the negative association of serum Mg level and IR in Mexican schoolchildren.

Overweight, Obesity, Hypertriglyceridemia, and Insulin Resistance Are Positively Associated with High Serum Copper Levels in Mexican Adults.

Recently, the role of trace elements in the pathophysiology of obesity, insulin resistance (IR), and metabolic diseases has been explored. In this cross-sectional study, we aimed to assess the association of overweight, obesity, and cardiometabolic traits with serum copper (Cu) levels in 346 Mexican adults. Serum Cu level was measured by inductively coupled plasma mass spectrometry (ICP-MS). Anthropometrical data were collected, and biochemical parameters were measured. The triglyceride-glucose (TyG) index was used as a surrogate marker to evaluate IR. Overweight and obesity status was positively associated with the serum Cu level (ß = 19.434 ± 7.309, p = 0.008). Serum Cu level was observed to have a positive association with serum triglycerides level (ß = 0.160 ± 0.045, p < 0.001) and TyG (ß = 0.001 ± 0.001, p < 0.001). Additionally, high serum Cu level was positively associated with overweight and obesity status (odds ratio [OR] = 1.9, 95% confidence interval [95% CI] 1.1-3.4, p = 0.014), hypertriglyceridemia (OR = 3.0, 95% CI 1.7-5.3, p < 0.001), and IR (OR = 2.6, 95% CI 1.4-4.6, p = 0.001). In conclusion, our results suggest that overweight, obesity, hypertriglyceridemia, and IR are positively associated with serum Cu levels in Mexican adults.

Efficient removal of triclosan from water through activated carbon adsorption and photodegradation processes.

This study investigated the application of adsorption with activated carbons (ACs) and photodegradation to reduce the concentration of triclosan (TCS) in aqueous solutions. Concerning adsorption, ACs (Darco, Norit, and F400) were characterised and batch experiments were performed to elucidate the effect of pH on equilibrium. The results showed that at pH = 7, the maximum adsorption capacity of TCS onto the ACs was 18.5 mg g-1 for Darco, 16.0 mg g-1 for Norit, and 15.5 mg g-1 for F400. The diffusional kinetic model allowed an adequate interpretation of the experimental data. The effective diffusivity varied and increased with the amount of TCS adsorbed, from 1.06 to 1.68 × 10-8 cm2 s-1. In the case of photodegradation, it was possible to ensure that the triclosan molecule was sensitive to UV light of 254 nm because the removal was over 80 % using UV light. The removal of TCS increased in the presence of sulfate radicals. It was possible to identify 2,4-dichlorophenol as one of the photolytic degradation products of triclosan, which does not represent an environmental hazard at low concentrations of triclosan in water. These results confirm that the use of AC Darco, Norit, and F400 and that photodegradation processes with UV light and persulfate radicals are effective in removing TCS from water, reaching concentration levels that do not constitute a risk to human health or environmental hazard. Both methods effectively eliminate pollutants with relatively easy techniques to implement.

Serum levels of anti-inflammatory/proinflammatory adipocytokines, and copper levels in overweight and obese women in an adult Mexican population.

BACKGROUND: An imbalance between adipokines and micronutrient concentrations, such as those of copper (Cu), has been linked to dysregulation of energy homeostasis leading to weight gain and the development of other comorbidities; however, information on this issue remains limited. Our aim was to investigate the correlation between Cu status and serum adipokine levels and their relationship in normal-weight, overweight, and obese adult women. METHODS: Sixty patients were evaluated and classified according to their body mass index (BMI) and biochemical parameters; adipokines and Cu were measured at fasting. RESULTS: Leptin (Lep) and resistin (Res) levels were elevated, whereas adiponectin (Adpn) and ghrelin (Ghr) values were decreased in overweight and obese women (p = 0.001). The mean Adpn/Lep ratio was <0.5 in overweight and obese subjects, while the Lep/Ghr ratio increased significantly in relation to weight gain, suggesting an inverse link between the ratios of these hormones in the regulation of obesity. The analysis revealed a positive association between BMI and Cu levels in obese women. Moreover, a negative association between Cu and Res in normal-weight subjects was found. CONCLUSIONS: Circulating fasting Res levels are negatively associated with serum Cu concentration in normal-weight adult women. We also observed a close relationship between Adpn/Lep and Lep/Ghr ratios with obesity. However, more observational studies are required to confirm these results in future research.

Relationship of Serum Zinc Levels with Cardiometabolic Traits in Overweight and Obese Schoolchildren from Mexico City.

Zinc (Zn) participates as a cofactor for many enzymes in the cellular metabolism, and its serum levels have been associated with different metabolic diseases, especially obesity (OB). Nevertheless, its associations are not clear in the children population. The objective of this study is to evaluate the association between serum Zn levels (SZn) with overweight/obesity status (OW/OB), as well as its cardiometabolic traits in a population of children in Mexico City. Anthropometrical data (body mass index z score (BMIz)), demographic variables (age and sex), and cardiometabolic traits (total cholesterol (TC), high-density lipoprotein cholesterol (HDLc), low-density lipoprotein cholesterol (LDLc), triglycerides (TG), fasting plasma glucose (FPG), and insulin) were analyzed in this cross-sectional study. SZn were measured by inductively coupled plasma mass spectrometry (ICP-MS). The population included 210 children from Mexico City (girls (n = 105) and boys (n = 105)) between ages 6 and 10 years. Normal-weight (NW) schoolchildren had higher SZn concentrations (66 µg/dL; IQR: 48 to 91) compared to OW or OB schoolchildren (61 µg/dL; IQR: 45 to 76). The data showed a significant negative association between SZn and BMIz without sex exclusion (r = - 0.181 and p = 0.009). The boy's population did not show an association between the SZn and BMIz compared to the girl's population which showed a significant negative association (r = - 0.277 and p = 0.004). In addition, other associations were found between SZn and TC (boys (r = 0.214 and p = 0.025), LDLc (boys (r = 0.213 and p = 0.029), and TG (girls (r = - 0.260 and p = 0.007)). Moreover, 38.6% of the total children in our population study had Zn deficiency (ZnD). NW schoolchildren had higher SZn concentrations compared to OW or OB schoolchildren. A diet low in Zn can be a factor to evaluate in the development of childhood OB in Mexico. However, further studies need to be performed on the children Mexican population to replicate and confirm our findings.

Overweight and Obesity Are Positively Associated with Serum Copper Levels in Mexican Schoolchildren.

Due to its relationship with oxidative stress and inflammation responses, obesity and its cardiometabolic implications have been related with serum copper (Cu). Hence, we analyzed the association of overweight (OW) and obesity (OB) status and cardiometabolic traits with serum Cu level in Mexican schoolchildren. Anthropometrical data and cardiometabolic traits were analyzed in this cross-sectional study. Serum Cu level was measured by inductively coupled plasma mass spectrometry. The study involved 191 schoolchildren (93 girls and 98 boys) with a mean age of 8.054 ± 1.170 years. Children with OW and OB had higher serum Cu levels than children with normal weight (NW) (mean difference: OW vs NW = 51.85 µg dL-1, OB vs NW = 47.22 µg dL-1, p < 0.001). In a multiple linear regression model, OW and OB status were positively associated with serum Cu levels (ßOW = 49.85, 95% confidence interval (95% CI) 35.84-63.87, p < 0.001; ßOB = 44.38, 95% CI 27.70-61.05, p < 0.001). We did not identify any significant association between cardiometabolic traits and serum Cu level. In conclusion, our results show an association of the presence of OW and OB with higher serum Cu levels, for the first time in Mexican schoolchildren. However, further functional studies are needed to better understand the role of Cu in the pathophysiology of obesity.

Relationship of thorium, uranium isotopes and uranium isotopic ratios with physicochemical parameters in cenote water from the Yucatán Peninsula.

Uranium (U) and Thorium (Th) concentrations are normally low in the water (<30 and 5 ng mL-1, respectively). However, we performed a direct analysis of 232Th, 234U, 235U and 238U in cenote water from the Yucatán Peninsula using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) as a rapid response technique to perform environmental radioactivity monitoring. Water samples were collected in 2021 from the cenotes and these were certificated by zones (PYNO, PYNE and PYSE) and monitoring depth [surface water (n = 52) and depth water (n = 48)]. Moreover, physicochemical parameters such as pH, electrical conductivity (EC), total dissolved solids (TDS), and temperature were measured in situ. Results obtained were total U and Th levels below permissible for human consumption. However, physicochemical parameters must be considered before use because it is outside the permissible limits in most cenotes. The median concentration value for 234U, 235U, 238U and 232Th in surface + depth water were 0.0001 ng mL-1, 0.0130 ng mL-1, 1.76 ng mL-1, and 0.062 ng mL-1, respectively. In addition, isotopic ratio of 235U/238U in surface + depth water was 0.00730. In addition, the PYNO zone showed a correlation between 232Th with EC and TDS. The PYSE zone showed a correlation between 232Th and temperature, and 235U/234U with pH, while PYEN did not show correlations. In conclusion, the first time evaluated U isotope concentrations and isotopic ratios of U and 232Th in cenote water from the Yucatán Peninsula, where U and Th concentrations were found below the permissible limits mentioned by guidelines for drinking-water quality. The average of 235U/238U is similar to isotopic ratios in "natural" water.

Sex-Specific Association between Fasting Plasma Glucose and Serum Selenium Levels in Adults from Southern Mexico.

Selenium (Se) is an essential trace element that by its antioxidant properties has been studied to elucidate its participation in the development of obesity and type 2 diabetes. We evaluated the association between cardiometabolic traits and serum Se levels in a sample of adults from southern Mexico. In 96 nondiabetic individuals, anthropometric data and clinical biochemistry measurements were analyzed. Serum total Se levels were measured with inductively coupled plasma mass spectrometry (ICP-MS). Serum Se level in the whole sample was 10.309 ± 3.031 µg mL-1 and no difference between the women and men was observed (p = 0.09). Additionally, fasting plasma glucose (FPG) was significantly associated with serum Se level (ß = -0.07 ± 0.03, p = 0.02, analysis adjusted for age, sex and BMI). Furthermore, sex shows significant interaction with FPG on the serum Se levels (p = 0.01). A follow-up analysis revealed the particular association between FPG and Se levels in women (ß = -0.10 ± 0.04, p = 0.01). In conclusion, our data evidenced a women-specific association between FPG and serum Se levels in a sample of adults from southern Mexico.

Serum zinc levels are associated with obesity and low-density lipoprotein cholesterol in Mexican adults.

PURPOSE: Little is known about the association between serum zinc (Zn) levels and obesity in the Mexican population. Therefore, we tested the association between serum Zn levels, obesity status, and serum lipid levels in a sample of Mexican adults. METHODS: Anthropometric data and serum levels of total cholesterol, high- and low-density lipoprotein cholesterol (HDL-C and LDL-C, respectively), and triglycerides were analyzed in 96 Mexican adults. Serum Zn was measured with inductively coupled plasma mass spectrometry. An individual data meta-analysis of the association between serum Zn, overweight, and obesity status was performed in 172 adults from two different provinces in Mexico. RESULTS: Serum Zn was negatively associated with body mass index (BMI, ß = -0.034 ± 0.013, p = 2.0 ×10-6) and obesity (odds ratio [OR]= 0.990, 95% confidence interval [CI]= 0.980-0.999, p = 3.4 ×10-5). The association between Zn level and obesity in Mexican adults was confirmed with an individual data meta-analysis (OR= 0.977, 95% CI= 0.966-0.988, p = 3.4 ×10-5). In addition, a significant interaction effect between serum Zn level and sex was observed on LDL-C level (ß = 7.010 ± 3.295, p = 0.037). Serum Zn was negatively associated with LDL-C levels in women (ß = -0.188 ± 0.074, p = 0.016). CONCLUSION: Our results confirm the negative association of serum Zn level with obesity. For the first time, we show a sex-specific association between serum Zn and LDL-C levels in a Mexican population. However, further studies are needed in larger and more varied Mexican cohorts to replicate and confirm our findings.

Serum lead levels and its association with overweight and obesity.

BACKGROUND: Lead (Pb) exposure has been associated with cardiovascular diseases and metabolic syndrome, nevertheless its association with obesity, type 2 diabetes, and dyslipidemia markers has been little explored in Mexico. Therefore, we evaluated the association of serum Pb levels (Pb-S), with body mass index (BMI), fasting plasma glucose (FPG), total cholesterol (TC), and triglycerides (TG). METHODS: A cross-sectional study was performed on 85 Mexican adults (57 women and 28 men). BMI was calculated, while FPG, TC, and TG were measured by the enzymatic colorimetric method. Total Pb-S levels were measured using inductively coupled plasma mass spectrometry (ICP-MS). RESULTS: The study population was 20.3 ± 1.9 years old, showed an average of Pb-S of 0.0982 ± 0.068 µg dL-1, and presented a frequency of overweight (OW) and obesity (OB) of 50.5% and 18.8%, respectively. Men had higher average FPG than women (Women= 83.930 ± 5.662 vs Men= 84.953 ± 6.495; p = 0.037). When we analyzed anthropometric and clinical variables, Pb-S and frequency of OW and OB were observed to increase within the categories of Pb-S tertiles (<0.001). The averages of Pb-S were 0.051 ± 0.035 µg dL-1, 0.107 ± 0.067 µg dL-1, and 0.151 ± 0.063 µg dL-1 for individuals with normal weight (NW), OW, and OB, respectively. In addition, an analysis adjusted for age and sex shows Pb-S is positively associated with BMI (ß = 2.76 ± 0.498, p = <0.001). CONCLUSION: Our results evidence a significant association between Pb-S and the increase of BMI in Mexican adults and highlight the important health impact that may represent environmental Pb exposure.

Relationship Between Serum Levels of Arsenic, Cadmium, and Mercury and Body Mass Index and Fasting Plasma Glucose in a Mexican Adult Population.

In Mexico, few studies have analyzed the associations between toxic elements and metabolic diseases. In the present study, we analyzed the associations between serum arsenic (As), cadmium (Cd), and mercury (Hg) levels and body mass index (BMI) and fasting plasma glucose (FPG) in a Mexican adult population. Anthropometric data corresponding to 86 Mexican healthy adults (59 females and 27 men) were analyzed. FPG was analyzed by an enzymatic colorimetric method, and serum As, Cd, and Hg levels were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). The data show that the median serum As, Cd, and Hg levels were relatively higher in females (As = 1.78 ng mL-1, Cd = 1.00 ng mL-1, Hg = 0.96 ng mL-1) than those in males (As = 1.22 ng mL-1, Cd = 0.91 ng mL-1, Hg = 0.95 ng mL-1). However, these differences were not statistically significant (p ≥ 0.097). We also found that the median level of As significantly increased with an increase in the body weight categories (normal weight = 1.08; overweight = 1.50; obesity = 2.75; p < 0.001). In addition, a positive association between serum As levels and FPG before and after adjustment for BMI was demonstrated (RhoUnadjusted = 0.012; (RhoAdjusted = 0.243, p = 0.032). Serum As levels are positively associated with BMI and FPG in the adult population of Mexico. Nevertheless, these results need to be replicated and confirmed with a larger sample size.

Geospatial modelling to estimate the territory at risk of establishment of influenza type A in Mexico - An ecological study.

The aim of this study was to estimate the territory at risk of establishment of influenza type A (EOITA) in Mexico, using geospatial models. A spatial database of 1973 outbreaks of influenza worldwide was used to develop risk models accounting for natural (natural threat), anthropic (man-made) and environmental (combination of the above) transmission. Then, a virus establishment risk model; an introduction model of influenza A developed in another study; and the three models mentioned were utilized using multi-criteria spatial evaluation supported by geographically weighted regression (GWR), receiver operating characteristic analysis and Moran's I. The results show that environmental risk was concentrated along the Gulf and Pacific coasts, the Yucatan Peninsula and southern Baja California. The identified risk for EOITA in Mexico were: 15.6% and 4.8%, by natural and anthropic risk, respectively, while 18.5% presented simultaneous environmental, natural and anthropic risk. Overall, 28.1% of localities in Mexico presented a High/High risk for the establishment of influenza type A (area under the curve=0.923, P<0.001; GWR, r2=0.840, P<0.001; Moran's I =0.79, P<0.001). Hence, these geospatial models were able to robustly estimate those areas susceptible to EOITA, where the results obtained show the relation between the geographical area and the different effects on health. The information obtained should help devising and directing strategies leading to efficient prevention and sound administration of both human and financial resources.

Comparison of a Brucella Enzyme Immunoassay and the Standard Agglutination with 2-Mercaptoethanol Test in the Diagnosis and Monitoring of Brucellosis in Mexican Patients.

BACKGROUND: The diagnosis of human brucellosis is difficult based on clinical grounds alone. Thus, the diagnosis is based on microbiological and serological tests. Therefore, the diagnosis relies predominantly on laboratory testing. The objective of this study was to determine the most efficient test for the diagnosis and monitoring of patients treated for brucellosis by comparing the standard agglutination test in a tube with 2-mercaptoethanol (SAT-2Me) to an enzyme-linked immunosorbent assay for the detection of antibodies against Brucella IgM (IgM ELISA). METHODS: A retrospective chart review was performed. A total of 108 patients with brucellosis were analyzed at diagnosis and at the first and second follow-ups after treatment. The data were captured and analyzed using the SPSS 18.0 program. Frequencies, percentages, the Pearson's chi-square test, the kappa coefficient, sensitivity, specificity, predictive values, odds ratio, and conditional odds ratio (OR and COR) were calculated. RESULTS: Diagnostic test: the IgM ELISA showed 96.3% sensitivity vs. 73.1% sensitivity for the SAT-2Me (p < 0.001). First follow-up: the IgM ELISA presented significant differences vs. the SAT-2Me in sensitivity (97.2% vs. 72.2%) and specificity (89.7% vs. 44.1%). Additionally, the second follow-up data showed significant differences in the sensitivity (85.7% vs. 71.4%) and specificity (82.8% vs. 41.4%) for the IgM ELISA vs. the SAT-2Me, re-spectively. In addition, the IgM ELISA showed significant concordance (0.836, p < 0.001 and 0.563, p < 0.001) at the first and second follow-ups, respectively, vs. the SAT-2Me. CONCLUSIONS: The IgM ELISA is a more reliable and useful assay for the diagnosis and monitoring of brucellosis patients than the SAT-2 Me, avoiding up to 45.6% of unnecessary treatments. The SAT-2Me showed lower efficiency for diagnosis than the IgM ELISA and limited relevance for monitoring.

Association of Serum Zinc Levels in Overweight and Obesity.

Low levels of zinc (Zn) have adverse effects on physiological and metabolic functions in humans, especially in processes linked with obesity. In this work, serum Zn levels and their associations with biochemical parameters (glucose, triglycerides, and total cholesterol), sex, and body mass index (BMI) were determined. The distribution of the study sample by sex was homogeneous: 52.6% were women and 47.4% were men. Women had higher BMI and Zn levels (normal weight and obesity) than men, but the differences in BMI and serum Zn levels by sex were not significant (p > 0.05). Nevertheless, the results obtained showed a decrease in serum Zn levels in overweight and obese individuals (p < 0.05) and a negative correlation between BMI and serum Zn levels (r = - 0.663 and p < 0.001); additionally, a significant correlation was identified between cholesterol and triglyceride values (r = 0.493 and p < 0.001). In conclusion, this study demonstrated decreased serum Zn levels in overweight and obese individuals.

Anomalous ratios of radioisotopes in PM10 as tracer of global fallout impact in the centre of Mexico.

The monitoring and evaluation of radioactive content in samples of PM10 aerosols have been investigated. The specific radioactivity concentrations (SRC) of 234U, 235U, 238U and 232Th were determined using inductively coupled plasma-sector field mass spectrometry in 13 samples collected in Mexico City and 8 samples collected in Cuernavaca in the centre of Mexico. The SRC of the radioisotopes analysed in PM10 were larger than those reported in PM2.5. The enrichment factor was greater than 5, indicating anthropogenic influences in both sites. The activity ratios of these isotopes in the samples were determined. The 235U/238U ratio showed variations with respect to the natural value, while the 234U/238U and 232Th/238U ratios did not show any secular equilibrium in all sites, corroborating that the increase of uranium is not influenced by natural sources. The annual dose results obtained have no impact on health.

Chronic Arsenic Exposure Increases Aß(1-42) Production and Receptor for Advanced Glycation End Products Expression in Rat Brain.

Chronic arsenic exposure during development is associated with alterations of chemical transmission and demyelination, which result in cognitive deficits and peripheral neuropathies. At the cellular level, arsenic toxicity involves increased generation of reactive species that induce severe cellular alterations such as DNA fragmentation, apoptosis, and lipid peroxidation. It has been proposed that arsenic-associated neurodegeneration could evolve to Alzheimer disease in later life.1,2 In this study, the effects of chronic exposure to inorganic arsenic (3 ppm by drinking water) in Wistar rats on the production and elimination of Amyloid-ß (Aß) were evaluated. Male Wistar rats were exposed to 3 ppm of arsenic in drinking water from fetal development until 4 months of age. After behavioral deficits induced by arsenic exposure through contextual fear conditioning were verified, the brains were collected for the determination of total arsenic by inductively coupled plasma-mass spectrometry, the levels of amyloid precursor protein and receptor for advanced glycation end products (RAGE) by Western blot analysis as well as their transcript levels by RT-qPCR, Aß(1-42) estimation by ELISA assay and the enzymatic activity of ß-secretase (BACE1). Our results demonstrate that chronic arsenic exposure induces behavioral deficits accompanied of higher levels of soluble and membranal RAGE and the increase of Aß(1-42) cleaved. In addition, BACE1 enzymatic activity was increased, while immunoblot assays showed no differences in the low-density lipoprotein receptor-related protein 1 (LRP1) receptor among groups. These results provide evidence of the effects of arsenic exposure on the production of Aß(1-42) and cerebral amyloid clearance through RAGE in an in vivo model that displays behavioral alterations. This work supports the hypothesis that early exposure to metals may contribute to neurodegeneration associated with amyloid accumulation.

Reassessment of 239Pu on planchets from human urine samples at ultra-trace levels using Aridus-ICPSFMS and AMS.

New analytical methods developed at the facilities here, based on two ultra-sensitive mass spectrometry (MS) techniques, inductively coupled plasma sector field mass spectrometer with a desolvator system (Aridus-ICP-SFMS) and accelerator MS (AMS), have been applied in this work for the reassessment of (239)Pu in alpha spectrometry (AS) planchets corresponding to spiked human urine samples. The obtained (239)Pu minimum detectable activities (MDAs) values by Aridus-ICP-SFMS and AMS were 3 fg (∼6.92 µBq) and 0.4 fg (∼0.92 µBq), respectively, per sample, which are much better than those attainable by AS [50 fg (∼115.3 µBq) of (239)Pu per sample, approximately]. Therefore, it is demonstrated that the MS techniques employed in this work are very powerful tools for internal dosimetry studies in human urine samples, giving excellent results when the reassessment of AS planchets is needed (samples with a Pu concentration below or at the MDA levels measurable by AS). This work is the continuation of an article published in J. Anal. At. Spectrom. 25 (1410-1415) 2010.

Evaluation of the inorganic selenium biotransformation in selenium-enriched yogurt by HPLC-ICP-MS.

Selenium is an essential element in the human diet. Interestingly, there has been an increased consumption of dietary supplements containing this element in the form of either inorganic or organic compounds. The effect of using selenium as a dietary supplement in yogurt has been evaluated. For this purpose, different concentrations of inorganic Se (ranging from 0.2 to 5000 microg g(-1)) have been added to milk before the fermentation process. Biotransformation of inorganic Se into organic species has been carefully evaluated by ion-exchange, reversed-phase, or size-exclusion chromatography, coupled to inductively coupled plasma mass spectrometry (ICP-MS). Yogurt fermentation in the presence of up to 2 microg g(-1) of Se(IV) produces a complete incorporation of this element into proteins as has been demonstrated applying a dialysis procedure. Analysis by SEC-ICP-MS showed that most of them have a molecular mass in the range of 30-70 kDa. Species determination after enzymatic hydrolysis has allowed the identification of Se-cystine using two different chromatographic systems. The biotransformation process that takes place during yogurt fermentation is very attractive because yogurt can act as a source of selenium supplementation.