Miguel Navarro-Alarcón

Selenium in food and the human body: A review

Selenium levels in soil generally reflect its presence in food and the Se levels in human populations. Se food content is influenced by geographical location, seasonal changes, protein content and food processing. Periodic monitoring of Se levels in soil and food is necessary. Diet is the major Se source and approximately 80% of dietary Se is absorbed depending on the type of food consumed. Se bioavailability varies according to the Se source and nutritional status of the subject, being significantly higher for organic forms of Se. Se supplements can be beneficial for subjects living in regions with very low environmental levels of Se. Several strategies have been followed: (1) employment of Se-enriched fertilizers; (2) supplementation of farm animals with Se; (3) consumption of multimicronutrient supplements with Se. Nevertheless, detailed investigations of possible interactions between Se supplements and other food components and their influence on Se bioavailability are needed. Suppliers also need to provide more information on the specific type of Se used in supplements. In addition, research is lacking on the mechanisms through which Se is involved in hepatocyte damage during hepatopathies. Although Se potential as an antioxidant for the prevention of cardiovascular diseases (CVD) is promising, additional long-term intervention trials are necessary. As a result, indiscriminate Se supplements cannot be reliably recommended for the prevention of CVD in human beings. Some interesting findings reported an association of Se intake with a reduced prevalence and risk for prostate and colon cancer. However, random trials for other cancer types are inconclusive. As a final conclusion, the general population should be warned against the employment of Se supplements for prevention of hepatopathies, cardiovascular or cancer diseases, because benefits of Se supplementation are still uncertain, and their indiscriminate use could generate an increased risk of Se toxicity.

Essentiality of selenium in the human body: relationship with different diseases.

In the present review different aspects related to the essential element selenium in the human organism are considered. A large number of human studies have been performed in order to improve knowledge on the influence of this element in the origin and development of several degenerative diseases. Selenium deficiencies among human beings as well as animals are being recognized worldwide to be related to a number of pathologies. This element has also the special characteristic that the range between its essential and toxic character is very close, and consequently daily dietary intake should be appropriately monitored in individuals. Nevertheless, nowadays there is still a lot of controversy about the optimum dietary level of this element in order to cure or to prevent the appearance of diseases such as cirrhosis, cancer, diabetes, or cardiovascular pathologies. Results obtained in several animal and epidemiological studies have indicated that Se could constitute a dietary factor with protective action against several degenerative diseases.

Beneficial effects of melatonin on obesity and lipid profile in young Zucker diabetic fatty rats

Abstract:  The study objective was to investigate the effects of melatonin on obesity and obesity‐associated systolic hypertension and dyslipidemia in young male Zucker diabetic fatty (ZDF) rats, an experimental model of the metabolic syndrome. ZDF rats (n = 30) and lean littermates (ZL) (n = 30) were used. At 6 wk of age, both lean and fatty animals were subdivided into three groups (n = 10): naive (N), vehicle‐treated (V), and melatonin‐treated (M) (10 mg/kg/day) for 6 wk. Vehicle and melatonin were added to the drinking water. Melatonin reduced mean weight gain (51 ± 2/100 g BW) versus N‐ZDF group (58 ± 3, P < 0.05) without food intake differences. M‐ZDF rats showed an apparent reduction in systolic hypertension that proved not to be statistically significant, and a significant improvement in dyslipidemia, with a reduction in hypertriglyceridemia from 580 ± 40 to 420.6 ± 40.9 mg/dL (P < 0.01). Melatonin raised high‐density‐lipoprotein (HDL) cholesterol in ZDF (from 81.6 ± 4.9 to 103.1 ± 4.5 mg/dL, P < 0.01) and ZL rats (from 62.8 ± 4.8 to 73.5 ± 4.8 mg/dL, P < 0.05) and significantly reduced low‐density‐lipoprotein (LDL) cholesterol in ZDF rats from 5.20 ± 0.4 to 4.14 ± 0.3 mg/dL (P < 0.05) but had no effect on total cholesterol levels. To our knowledge, this is the first evidence of a positive effect of melatonin on overweight and lipid pattern of obese Zucker diabetic rats, supporting the proposition that melatonin administration may ameliorate overweight and lipid metabolism in humans. Because these benefits occurred in youth, before advanced metabolic and vascular complications, melatonin might help to prevent cardiovascular disease associated with obesity and dyslipidemia.

Melatonin ameliorates low-grade inflammation and oxidative stress in young Zucker diabetic fatty rats

The aim of this study was to investigate the effects of melatonin on low‐grade inflammation and oxidative stress in young male Zucker diabetic fatty (ZDF) rats, an experimental model of metabolic syndrome and type 2 diabetes mellitus (T2DM). ZDF rats (n = 30) and lean littermates (ZL) (n = 30) were used. At 6 wk of age, both lean and fatty animals were subdivided into three groups, each composed of 10 rats: naive (N), vehicle treated (V), and melatonin treated (M) (10 mg/kg/day) for 6 wk. Vehicle and melatonin were added to the drinking water. Pro‐inflammatory state was evaluated by plasma levels of interleukin‐6 (IL‐6), tumor necrosis factor‐α (TNF‐α), and C‐reactive protein (CRP). Also, oxidative stress was assessed by plasma lipid peroxidation (LPO), both basal and after Fe2+/H2O2 inducement. ZDF rats exhibited higher levels of IL‐6 (112.4 ± 1.5 pg/mL), TNF‐α (11.0 ± 0.1 pg/mL) and CRP (828 ± 16.0 µg/mL) compared with lean rats (IL‐6, 89.9 ± 1.0, P < 0.01; TNF‐α, 9.7 ± 0.4, P < 0.01; CRP, 508 ± 21.5, P < 0.001). Melatonin lowered IL‐6 (10%, P < 0.05), TNF‐α (10%, P < 0.05), and CRP (21%, P < 0.01). Basal and Fe2+/H2O2‐induced LPO, expressed as malondialdehyde equivalents (µmol/L), were higher in ZDF rats (basal, 3.2 ± 0.1 versus 2.5 ± 0.1 in ZL, P < 0.01; Fe2+/H2O2‐induced, 8.7 ± 0.2 versus 5.5 ± 0.3 in ZL; P < 0.001). Melatonin improved basal LPO (15%, P < 0.05) in ZDF rats, and Fe2+/H2O2‐ induced LPO in both ZL (15.2%, P < 0.01) and ZDF rats (39%, P < 0.001). These results demonstrated that oral melatonin administration ameliorates the pro‐inflammatory state and oxidative stress, which underlie the development of insulin resistance and their consequences, metabolic syndrome, diabetes, and cardiovascular disease.

Serum Zinc and Copper Concentrations and Cu/Zn ratios in Patients with Hepatopathies or Diabetes

The serum zinc and copper levels, as well as Zn/Cu ratios, were determined in 30 patients (18 with diabetes and 12 with hepatopathies) and compared to healthy-age matched controls by atomic absorption spectrometry. Serum Zn (0.946 +/- 0.302 mg/l) and Cu (0.952 +/- 0.355 mg/l) concentrations were not significantly different in patients with hepatopathies as compared to controls (p > 0.05). Serum Zn concentrations (0.778 +/- 0.164 mg/l) were significantly lower in diabetic patients than those determined in controls (p < 0.01). In contrast, Cu levels (0.987 +/- 0.305 mg/l) were not significantly different (p > 0.05) than in controls. Serum Cu/Zn ratios were not significantly different in patients with diabetes or hepatopathies than those measured in healthy controls (p > 0.05). In patients, no statistically significant differences were observed in the Zn, Cu and Cu/Zn with respect to sex (p > 0.05) or age (p > 0.05).

Longitudinal study of serum zinc and copper levels in hemodialysis patients and their relation to biochemical markers

A 6-mo longitudinal study of 48 hemodialysis patients (HPs) with chronic renal failure was performed. Three blood samplings were done. Samples of whole blood from each patient were collected during hemodialysis sessions after passing through the artificial kidney. Zinc and copper levels were measured by atomic absorption spectrometry. Additionally, 36 biochemical indexes were evaluated during the study. Fifty-two healthy matched controls were also considered. Mean serum zinc and copper concentrations in HPs were significantly decreased (Zn) and increased (Cu), when compared with healthy controls (p<0.01). Zinc concentrations found in the first and second blood samplings from patients were significantly lower than those measured for the third sampling (p<0.01). The etiology of chronic renal failure influenced the statistically serum Zn levels of patients (p<0.05). Serum copper levels of HPs were significantly diminished by the existence of secondary associated diseases (p<0.01). Uric acid and parathyroid hormone, and total-cholesterol and glutamic-pyruvic-transaminase levels were significantly (p<0.05) and linearly related with serum zinc and copper concentrations, respectively. From all of indexes, creatinine, direct bilirubin, magnesium, calcium, parathyroid hormone, transferrin, and albumin were statistically modified along the longitudinal study (p<0.05). Transferrin serum levels were significantly diminished in the third blood sampling, indicating the tendency toward anemia in the patients. This result is reinforced by low levels of biochemical and hematological indexes related with iron body staus.

Magnesium and calcium contents in foods from SE Spain: influencing factors and estimation of daily dietary intakes.

The magnesium and calcium content (fresh weight basis) of 243 food, 69 beverages and 11 potable water samples were determined using flame atomic absorption spectrometry. Analyses of NIST and CBR-CEC reference materials demonstrated the reliability and accuracy of this technique. The highest magnesium and calcium levels corresponded to molluscs and crustacea, and dairy products, respectively. Magnesium concentrations found in different food groups were significantly and linearly related with corresponding calcium levels (P<0.001) with the exception of fish products. Significant linear relationships among magnesium and calcium concentrations, and fiber content for cereals, legumes and dry-fruits were found (P<0.001); however, total fat contents of considered foods were not related (P>0.05) with levels of elements considered. Significant linear relationships among magnesium and calcium concentrations in cereals, legumes and fruits, and protein content were found (P<0.001). In meat and by-products, magnesium concentrations found in organ meats were significantly lower (P<0.01); for calcium, levels measured in sausages were significantly higher (P<0.001) than those found in meats and organ meats. In fish products, magnesium levels in molluscs and crustacea were significantly higher than those measured in fish and cephalopoda (P<0.001); for calcium, concentrations in cephalopoda were significantly lower (P<0.001). Mean magnesium and calcium concentrations analyzed in cheese were statistically higher than those determined in other dairy products (P<0.01). In alcoholic drinks, magnesium and calcium levels measured in distilled beverages (whisky, gin, rum, brandy and alcoholic liquors) were statistically lower than those found in fermented types (wine and beer) (P<0.01). The daily intake of magnesium and calcium in the Spanish diet was 366.1 and 1266.6 mg/day per person, respectively. Results revealed that the intake of analyzed elements was similar to recommended dietary allowances.

ZINC AND COPPER CONCENTRATIONS IN SERUM FROM SPANISH WOMEN DURING PREGNANCY

A cross-sectional study of serum zinc (Zn) and copper (Cu) levels in 31 healthy pregnant women and 51 healthy, nonpregnant controls living in the Mediterranean area of Granada, Spain, was performed. The subjects were divided into two groups: Group A, consisted of pregnant women in three categories according to the trimester of pregnancy, and Group B consisted of nonpregnant women acting as controls.In pregnant women, serum Zn levels were found from 0.300-1.340 mg/L and serum Cu from 0.936-2.304 mg/L, whereas in the nonpregnant women group, the mean serum levels were 0.947 ±0.265 mg/L for Zn and 1.092 ±0.365 mg/L for Cu. Serum Zn progressively decreased with gestation. Mean Zn levels were 0.829 ±0.253, 0.846 ±0.329, and 0.620 ±0.142 mg/L, corresponding to the first, second, and third trimesters of pregnancy, respectively.Serum Zn concentrations were significantly lower in pregnant women as compared to controls: 0.712 ±0.236 mg/L vs 0.947 ±0.265 mg/L, respectively (p < 0.05).In contrast, Cu levels increased with period of gestation from 1.053 ±0.498 mg/L in the first trimester to 1.616 ±0.304 mg/L in the second and 1.689 ±0.344 mg/L in the third. Serum Cu levels in the second and third trimesters of pregnancy were significantly higher (p < 0.05) than those determined during the first trimester and for nonpregnant controls. Both Zn and Cu during pregnancy did not appear to be dependent on the subject’s age (p > 0.05).

Determination of copper levels in serum of healthy subjects by atomic absorption spectrometry

Copper levels in serum samples of 84 healthy subjects living in southeastern Spain were determined using the flame atomic absorption spectrometry technique. Mineralization of samples was carried out with an HNO3/HClO4 (4:1) mixture in a thermostated mineralization block. The accuracy of the method was tested by using a standard reference material. A mean recovery percentage of 104.70% was obtained. The relative standard deviation (R.S.D.) as a measurement of the precision of the method was lower than 5% in the concentration range considered. Mean copper concentrations were 1.092 +/- 0.365 mg/l (with the range 0.304-2.000 mg/l) and 1.113 +/- 0.253 mg/l (corresponding to an interval of 0.648-1.760 mg/l) for women and men, respectively. There are no significant differences between the copper levels in serum according to either sex or geography zone (P > 0.05). For example, there were no differences of copper levels in serum of subjects from coastal and mountainous zones. Estimated daily dietary intakes on copper in women and men were 1.38 and 2.10 mg Cu/day respectively.

Determination of selenium in cereals, legumes and dry fruits from southeastern Spain for calculation of daily dietary intake.

Hydride generation atomic absorption spectrometry was used to determine selenium content in cereals, legumes and dry fruits from the coast of the province of Granada (southeastern Spain). Accuracy was assured using both a NIST SRM 1572 and recovery experiments. The precision expressed as relative standard deviation (R.S.D.) varied between 6.50% for seeds and 15.98% for bread. The highest selenium concentrations were found for dry fruits (294.6 ng/g), followed by legumes (111.8 ng/g), and the lowest for cereals (27.8 ng/g). Considering the average daily individual consumption of these foods in Andalusia (southern Spain), the daily dietary intake of selenium supplied by this source is 15.36 micrograms/day for an adult. The content of total selenium in corn samples taken from the zone is independent of both human and industrial activities (P > 0.05).