Serum concentrations of vitamins A and E in impaired glucose tolerance

Vitamin A homeostasis and cardiometabolic disease in humans: lost in translation?

Vitamin A (retinol) is an essential, fat-soluble vitamin that plays critical roles in embryonic development, vision, immunity, and reproduction. Severe vitamin A deficiency results in profound embryonic dysgenesis, blindness, and infertility. The roles of bioactive vitamin A metabolites in regulating cell proliferation, cellular differentiation, and immune cell function form the basis of their clinical use in the treatment of dermatologic conditions and hematologic malignancies. Increasingly, vitamin A also has been recognized to play important roles in cardiometabolic health, including the regulation of adipogenesis, energy partitioning, and lipoprotein metabolism. While these roles are strongly supported by animal and in vitro studies, they remain poorly understood in human physiology and disease. This review briefly introduces vitamin A biology and presents the key preclinical data that have generated interest in vitamin A as a mediator of cardiometabolic health. The review also summarizes clinical studies performed to date, highlighting the limitations of many of these studies and the ongoing controversies in the field. Finally, additional perspectives are suggested that may help position vitamin A metabolism within a broader biological context and thereby contribute to enhanced understanding of vitamin A's complex roles in clinical cardiometabolic disease.

Associations between Adherence to the Taiwan Dietary Reference Intakes of Micronutrients and the Risk of Type 2 Diabetes

The dietary reference intakes (DRIs) were established as guidance for the intake of micronutrients and other nutrients. However, how DRIs affect disease status has not been thoroughly examined. The aim of this study is to examine the associations between adherence to the DRIs of selected micronutrients and type 2 diabetes. A populational and cross-sectional study was conducted using data from the Nutrition and Health Survey in Taiwan (NAHSIT) 2013-2016. A total of 14 nutrient intakes, including those for vitamin A, C, D, E, B1, B2, B3, B6, B12, iron, magnesium, zinc, calcium, and phosphorus, were evaluated using the 24 h dietary recall method. Type 2 diabetes was defined as a fasting serum HbA1c level of 6.5% or higher and excluded participants who had received treatments for type 2 diabetes or reported a diagnosis of type 2 diabetes by physicians to avoid the possible inverse association. A total of 2685 participants aged 19 and above were included in the final analysis. After adjusting for confounders, we found that adherence to the DRI of vitamin A was associated with a reduced risk of type 2 diabetes among men. The odds ratio (OR) was 0.64 (95% confidence interval (CI) = 0.42-0.99) compared with men who did not adhere to the DRI. As for women, we found that adherence to the DRI of vitamin B1 was associated with a reduced risk of type 2 diabetes. The OR was 0.59 (95% CI = 0.35-0.97) compared with that for women who did not adhere to the DRI. This study showed that adherence to Taiwan DRIs of vitamin A for men and vitamin B1 for women might have beneficial effects on type 2 diabetes.

All-trans retinoic acid impairs glucose-stimulated insulin secretion by activating the RXR/SREBP-1c/UCP2 pathway

Diabetes is often associated with vitamin A disorders. All-trans retinoic acid (ATRA) is the main active constituent of vitamin A. We aimed to investigate whether ATRA influences diabetic progression and its mechanisms using both Goto-Kazizazi (GK) rats and INS-1 cells. Rat experiments demonstrated that ATRA treatment worsened diabetes symptoms, as evidenced by an increase in fasting blood glucose (FBG) levels and impairment of glucose homeostasis. Importantly, ATRA impaired glucose-stimulated insulin secretion (GSIS) and increased the expression of sterol regulatory element-binding protein 1c (SREBP-1c) and uncoupling protein 2 (UCP2) in the rat pancreas. Data from INS-1 cells also showed that ATRA upregulated SREBP-1c and UCP2 expression and impaired GSIS at 23 mM glucose. Srebp-1c or Ucp2 silencing attenuated GSIS impairment by reversing the ATRA-induced increase in UCP2 expression and decrease in ATP content. ATRA and the retinoid X receptor (RXR) agonists 9-cis RA and LG100268 induced the gene expression of Srebp-1c, which was almost completely abolished by the RXR antagonist HX531. RXRα-LBD luciferase reporter plasmid experiments also demonstrated that ATRA concentration-dependently activated RXRα, the EC₅₀ of which was 1.37 μM, which was lower than the ATRA concentration in the pancreas of GK rats treated with a high dose of ATRA (approximately 3 μM), inferring that ATRA can upregulate Srebp-1c expression in the pancreas by activating RXR. In conclusion, ATRA impaired GSIS partly by activating the RXR/SREBP-1c/UCP2 pathway, thus worsening diabetic symptoms. The results highlight the roles of ATRA in diabetic progression and establish new strategies for diabetes treatment.

The Association and Mediating Biomarkers of Serum Retinol in Influencing the Development of Type 2 Diabetes: A Prospective Cohort Study in Middle-Aged and Elderly Population

The aims of this research are to elucidate whether serum retinol is associated with type 2 diabetes and to explore the underlying mechanisms of the association in a prospective cohort study. A total of 3,526 diabetes-free participants aged 40 years or older were enrolled at baseline in 2010–2012. Multivariable logistic regression was adopted to evaluate the associations of serum retinol and dietary vitamin A (VA) intake with type 2 diabetes. Mediation analyses were used to reveal potential mediators in their associations. After a mean follow-up of 5.3 years, 280 incident cases of type 2 diabetes occurred. Serum retinol was positively associated with the incidence of type 2 diabetes. The multivariable-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for type 2 diabetes from the bottom to the top quintile of serum retinol were 1, 1.878 (1.202, 2.936), 2.110 (1.364, 3.263), 1.614 (1.027, 2.538), and 2.134 (1.377, 3.306) (p-trend = 0.009), respectively. Mediation analysis showed that increased homeostasis model assessment - insulin resistance HOMA-IR, triglycerides (TG), and serum xanthine oxidase (XO) activity could account for 8.5, 14.7, and 12.1% of the total effects of serum retinol on type 2 diabetes, respectively. Serum retinol concentration was not significantly associated with dietary VA intake (r = −0.010, p = 0.570). In addition, no significant relationship was observed between dietary VA intake and the risk of type 2 diabetes. Overall, elevated serum retinol might increase the risk of type 2 diabetes which is mainly mediated by increased insulin resistance, TG, or serum XO activity.

Vitamin A and Diabetes

Recently, research data have shown that vitamin A (VA, retinol) as a micronutrient participates in the regulation of glucose and lipid metabolism. Since diabetes is a metabolic disease, it is imperative to reveal the relationship of VA and diabetes. This review was aimed to summarize the current understanding of VA and its metabolites in diabetes. Since April of 2020, the authors have searched the PubMed using key words and retrieved articles that focused on diabetes and VA or its metabolites. Based on the published data, it appears that the development of type 1 diabetes leads to reduction of blood VA level in human and animals, and increase of hepatic VA store in experimental animals. On the other hand, the mutual impacts of type 2 diabetes and VA intake and blood VA level on each other appear to be uncertain. Retinoic acid, the active metabolite of VA, has been studied extensively for the treatment of diabetic complications. The current data appear to indicate that the development of diabetes is associated with changes of VA metabolism. More carefully designed clinical and laboratory experiments are needed to reveal the impacts of diabetes on VA metabolism and the role of VA in the development and treatment of diabetes.

Vitamin A levels are decreased but not influenced by glucose- or lipid-lowering medications in subjects with type 2 diabetes

Background and aim

Type 2 diabetes (T2D) is a complex polygenic disease with unclear mechanisms. Clinical studies on the association of vitamin A with T2D in humans are still controversial. Herein, we aimed to investigate the plasma levels of vitamin A, predictor factors, and its correlations with clinical phenotypes in Emirati population. The effect of glucose-and lipid-lowering medications on vitamin A levels was also studied.

Methods

A cross-sectional cohort comprised 158 T2D-subjects and 90 healthy controls were recruited from the United Arab Emirates National Diabetes Study (UAEDIAB). All anthropometric, clinical, and biomedical measurements were collected. Plasma levels of vitamin A were determined using ELISA assay.

Results

Levels of vitamin A were significantly lower in T2D-subjects compared to healthy control (p < 0.01). Vitamin A levels were unaffected by gender base and inversely correlated with age, fasting blood glucose (FBG), glycated hemoglobin (HbA1c), waist circumference, triglycerides, and body mass index (BMI). Regression analysis revealed that HbA1c and age are predictors for vitamin A. Intake of glucose- or lipid-lowering medications showed no effect on vitamin A levels.

Conclusion

HbA1c and age are predictors for low levels of vitamin A among Emirati-T2D subjects. No influence of glucose and lipid-lowering medications on the plasma levels of vitamin A.

Vitamin A and Its Multi-Effects on Pancreas: Recent Advances and Prospects

Vitamin A (VA), which is stored in several forms in most tissues, is required to maintain metabolite homeostasis and other processes, including the visual cycle, energy balance, epithelial cell integrity, and infection resistance. In recent years, VA molecules, also known as retinoids, have been extensively explored and used in the treatment of skin disorders and immune-related tumors. To date, several observational and interventional studies have explored the relationship between VA status and the pathogenesis of diabetes. In particular, VA micronutrients have been shown to regulate pancreatic development, β-cell function, pancreatic innate immune responses, and pancreatic stellate cells phenotypes through multiple mechanisms. However, there are still many problems to be proven or resolved. In this review, we summarize and discuss recent and available evidence on VA biological metabolism in the pancreas. Analysis of the effects of VA on metabolism in the pancreas will contribute to our understanding of the supportive physiological roles of VA in pancreas protection.

Dietary β-Carotene Rescues Vitamin A Deficiency and Inhibits Atherogenesis in Apolipoprotein E-Deficient Mice

Vitamin A deficiency (VAD) is a major health problem, especially in developing countries. In this study, we investigated the effect of VAD from weaning to adulthood in apoE^−/− mice. Three-week-old male mice were allocated into four diet groups: I. VAD II. VAD+vitamin A (VA), 1500 IU retinyl-palmitate; III. VAD+β-carotene (BC), 6 g/kg feed, containing 50% all-trans and 50% 9-cis BC. IV. VAD with BC and VA (BC+VA). After 13 weeks, we assessed the size of atherosclerotic plaques and measured VA in tissues and BC in plasma and tissues. VAD resulted in diminished hepatic VA levels and undetectable brain VA levels compared to the other groups. BC completely replenished VA levels in the liver, and BC+VA led to a two-fold elevation of hepatic VA accumulation. In adipose tissue, mice fed BC+VA accumulated only 13% BC compared to mice fed BC alone. Atherosclerotic lesion area of BC group was 73% lower compared to VAD group (p < 0.05). These results suggest that BC can be a sole source for VA and inhibits atherogenesis.

Retinol, Retinoic Acid, and Retinol-Binding Protein 4 are Differentially Associated with Cardiovascular Disease, Type 2 Diabetes, and Obesity: An Overview of Human Studies

Vitamin A is a fat-soluble essential nutrient obtained from plant- and animal-based sources that has roles in growth, vision, and metabolism. Vitamin A circulates mainly as retinol bound to retinol-binding protein 4 (RBP4), and is delivered to tissues and converted to retinoic acid, which is a ligand for several nuclear receptors. In recent years, aspects of vitamin A metabolism have been under scrutiny with regards to the development of metabolic and lifestyle diseases including cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), and overweight and obesity in humans. Studies have mainly focused on RBP4 in this context, whereas the major circulating form, retinol, and the major bioactive form, retinoic acid, have been overlooked in this regard until recently. As one of the main roles of RBP4 is to deliver retinol to tissues for biological action, the associations of retinol and retinoic acid with these diseases must also be considered. In this review, we summarize and discuss recent and available evidence from human studies with focus on retinol, retinoic acid, and RBP4 and provide an overview of these crucial components of vitamin A metabolism in CVD, T2DM, and obesity. In summary, retinol was found to be both inversely and positively associated with CVD whereas the associations with T2DM and obesity were less clear. Although only a few studies have been published on retinoic acid, it was inversely associated with CVD. In contrast, serum RBP4 was mostly found to be positively associated with CVD, T2DM, and obesity. At present, it is difficult to ascertain why the reported associations differ depending on the compound under study, but there is a clear imbalance in the literature in disfavor of retinol and retinoic acid, which needs to be considered in future human studies.

Obesity and Insulin Resistance Are Inversely Associated with Serum and Adipose Tissue Carotenoid Concentrations in Adults

BACKGROUND

Low tissue concentrations of carotenoids have been suggested to contribute to insulin resistance in obesity.

OBJECTIVES

The objectives of the study were to 1) evaluate the relations of adipose tissue and serum carotenoids with body fat, abdominal fat distribution, muscle, adipose tissue and liver insulin resistance, and dietary intake; 2) evaluate the relations and distributions of carotenoids detected in adipose tissue and serum; and 3) compare serum carotenoids and retinol concentrations in subjects with and without obesity.

METHODS

Post hoc analysis of serum and adipose tissue carotenoids in individuals [n = 80; 31 men, 49 women; age (mean ± SEM): 51.4 ± 1.1 y] who participated in 2 separate studies conducted at the Clinical Research Facility at the Garvan Institute of Medical Research (Sydney) between 2008 and 2013. Retinol, α-carotene, β-carotene, ζ-carotene, lutein, lycopene, phytoene, and phytofluene were measured using HPLC. Body composition was measured by dual-energy X-ray absorptiometry. Insulin resistance was measured by 2-step hyperinsulinemic-euglycemic clamps with deuterated glucose (n = 64), and subcutaneous and visceral abdominal volume and liver and pancreatic fat by MRI (n = 60). Periumbilical subcutaneous fat biopsy was performed and carotenoids and retinol measured in the tissue (n = 16).

RESULTS

We found that ζ-carotene, phytoene, and phytofluene were stored in considerable amounts in adipose tissue (25% of adipose tissue carotenoids). Carotenoid concentrations in adipose tissue and serum correlated significantly, but they followed different distributions: ζ-carotene was 3-fold higher in adipose tissue compared with serum, while lutein and lycopene made up 20% and 21% of serum carotenoids compared with 2% and 12% of adipose tissue carotenoids, respectively. Liver (P ≤ 0.028) and adipose tissue (P = 0.023), but not muscle (P ≥ 0.16), insulin resistance correlated inversely with many of the serum carotenoids.

CONCLUSIONS

Multiple serum and adipose tissue carotenoids are associated with favorable metabolic traits, including insulin sensitivity in liver and adipose tissue in humans.

Impaired glucose tolerance and metformin: clinical and mechanistic aspects

The Diabetes Prevention Program (DPP) showed that metformin reduced the incidence of diabetes in subjects with impaired glucose tolerance (IGT) who were at high risk of progression to type 2 diabetes. Metformin was not as efficient as intensive life style intervention, but had a clinically significant effect in obese individuals and in those with impaired fasting glucose (IFG). This review discusses the clinical implications and the mechanistic aspects of the effect of metformin in IGT and IFG. Acute actions of metformin on postprandial metabolism to improve hepatic glucose handling and improve the lipid profile could contribute to the lower incidence of diabetes. Longer term improvements in haemodynamic parameters and reduced oxidative stress are also implicated. Metformin offers a potential alternative or complement to lifestyle intervention for IGT, and deserves further evaluation in this respect.

Vitamin A: a missing link in diabetes?

Vitamin A has a critical role in embryonic development, immunity and the visual cycle. In recent years, evidence has demonstrated that vitamin A can also regulate metabolic pathways implicated in the pathogenesis of obesity and diabetes. This has increased interest in the possible antiobesity and antidiabetic properties of natural and synthetic vitamin A derivatives. However, whether vitamin A deficiency or aberrations in vitamin A metabolism contribute to the pathogenesis of diabetes is not known. This perspective article will review what is currently known and new data regarding the link between vitamin A and the clinical manifestations of common and atypical forms of diabetes.

Plasma concentrations of retinol in obese children and adolescents: relationship to metabolic syndrome components

Objective:

To evaluate obese children and adolescents' retinol plasma levels and to correlate them with metabolic syndrome components.

Methods:

Cross-sectional study with 61 obese children and adolescents (body mass index Z score - ZBMI>+2). Pubertal development, arterial blood pressure, body weight and height for nutritional classification and waist circumference were obtained. A 15mL blood sample was collected (after a 12-hour fasting in a low luminosity room) for retinol determination (cut-off inadequate if <30µg/dL), lipid profile (HDL-c, LDL-c, and triglycerides), oral glucose tolerance test (fasting and 120 minutes) and for high sensitivity C-reactive protein. Spearman correlation and multiple linear regression were used in the statistical analysis.

Results:

Mean age was 10.7±2.7 years. There was a predominance of male gender 38/61 (62%) and pre-pubertal 35/61 (57%) subjects. The average plasmatic retinol was 48.5±18.6ug/dL. Retinol deficiency and severe obesity were observed in 6/61 (10%) and 36/61 (59%), respectively. Glucose level at 120 minutes was the independent and predictive variable of plasma retinol levels [β=-0.286 (95%CI -0.013 - -0.001)].

Conclusions:

An independent and inverse association between plasma retinol levels and glucose tolerance was observed, suggesting an important contribution of this vitamin in the morbidities associated to obesity in children and adolescents.

Micronutrient status in type 2 diabetes: a review

Type 2 diabetes is characterized by significant losses of important micronutrients due to metabolic basis of the disease and its complications. Evidence of changes in trace mineral and vitamin metabolism as a consequence of type 2 diabetes is reviewed in this chapter. This review is not a meta-analysis but an overview of the micronutrient status, metabolic needs, and potential micronutrient requirements in type 2 diabetics. This chapter will not concentrate on vitamin D and type 2 diabetes as this is a topic that has been extensively reviewed before. The less well-known micronutrients notably zinc, magnesium, chromium, copper, manganese, iron, selenium, vanadium, B-group vitamins, and certain antioxidants are assessed. While some evidence is available to demonstrate the positive influence of micronutrient supplementation on glycemic control, much remains to be investigated. Additional research is necessary to characterize better biomarkers of micronutrient status and requirements in type 2 diabetics. The optimal level of micronutrient supplementation to achieve glucose homeostasis in type 2 diabetics remains a challenge.

Retinoid metabolism and diabetes mellitus

Retinoid acid is a metabolite of vitamin A and functions as an important factor in cell survival, differentiation and death. Most previous studies on retinoid metabolism have focused on its association with cancer, hematologic and dermatologic disorders. Given the special concern over the recent increase in the prevalence of diabetes worldwide, the role of retinoid metabolism on glucose metabolism and insulin resistance in the human body is of marked importance. Therefore, in this issue, we review the literature on the association of retinoid metabolism with glucose tolerance, with regard to insulin secretion, pancreatic autoimmunity, insulin sensitivity and lipid metabolism. Further, we tried to assess the possibility of using retinoids as a novel therapeutic strategy for diabetes.

Relation between glucose levels, high-sensitivity C-reactive protein (hs-CRP), body mass index (BMI) and serum and dietary retinol in elderly in population-based study

The aim of this study was to evaluate the relationships between fasting glucose levels, hs-CRP, BMI and serum retinol and diet in elderly people. For this study, a cross-sectional, epidemiological, population-based format was adopted. One hundred and sixty-three individuals between 60 and 90 years of age participated; the participants were from different socioeconomic and health backgrounds, except for the individuals diagnosed with diabetes. Most subjects had serum concentrations in the reference ranges for all variables. There was not a significant relationship between fasting glucose and serum retinol or diet. There was a significant correlation between hs-CRP and BMI (r=0.22, p=0.0082) and hs-CRP and total calorie intake (p=0.0091), which reinforces the notion that an increased intake of calories results in being overweight and/or obese. Considering the importance of vitamin A in various physiological processes, more studies on these relationships are necessary to establish a recommendation of vitamin A for the treatment and prevention of changes in fasting glucose and obesity in the elderly population.

The effects of 17beta-estradiol and vitamin E treatments on oxidative stress and antioxidant levels in brain cortex of diabetic ovariectomized rats

We investigated the effects of 17beta-estradiol (E 2 ) and vitamin E on lipid peroxidation and antioxidant levels in brain cortex of diabetic ovariectomized (OVX) rats. Forty-two rats were equally divided into seven groups: Control; OVX; OVX+E 2 ; OVX+E 2 +vitamin E; OVX+diabetic; OVX+diabetic+E 2 and OVX+diabetic+E 2 +vitamin E. Then, E 2 (40 microg kg -1 /day) and vitamin E (100 mg kg -1 /day) were given. Glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD), glutathione (GSH), vitamin A and beta-carotene in brain were decreased (p<0.05) when compared with control in OVX but MDA in brain and glucose in plasma were elevated (p<0.05). The antioxidant levels in brain (p<0.05) increased although MDA (p<0.05) in brain and glucose (p<0.05, p<0.01) in plasma decreased in OVX after E 2 and E 2 +vitamin E supplementation. The activities of GSH-Px (p<0.001, p<0.01), CAT (p<005, p<0.001) and SOD (p<0.001) and the levels of GSH (p<0.001), vitamin A (p<0.05) and beta-carotene (p<0.001, p<0.05) were lower in the brain of OVX diabetic rats, while MDA in the brain and glucose in the plasma were higher (p<0.001). The antioxidant enzymes (p<0.05, p<0.01), GSH, vitamin A and beta-carotene (p<0.01, p<0.001) in brain increased while MDA in brain and glucose in plasma decreased (p<0.01, p<0.001) in diabetic OVX after treatments. Finally, the E 2 and E 2 +vitamin E supplementation to diabetic OVX and OVX rats may strengthen the antioxidant system by reducing lipid peroxidation.

The effects of diabetes mellitus, age, and vitamin E on testicular oxidative stress

OBJECTIVE

To examine the effects of age and/or diabetes on oxidative stress and steroidogenesis, and the protective effect of vitamin E in testis tissue.

DESIGN

Controlled experimental study.

SETTING

Pamukkale University School of Medicine animal facility.

ANIMAL(S)

Male Wistar rats divided into six groups with six animals in each group: young control; young diabetic; young diabetic with vitamin E treatment; aged control; aged diabetic; and aged diabetic with vitamin E treatment.

INTERVENTION(S)

Diabetes was induced by a single intraperitoneal injection of 50 mg/kg streptozotocin and was confirmed by testing blood glucose levels 5 to 7 days after injection. Vitamin E was administered orally for 6 weeks.

MAIN OUTCOME MEASURE(S)

Serum testosterone and tissue malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) levels were measured, and testis tissue was examined histopathologically.

RESULT(S)

Elevated malondialdehyde and reduced superoxide dismutase, glutathione, and serum testosterone levels were detected only in the young and aged-diabetic groups. Histopathologic change was not detected in the testis tissue in any of the groups.

CONCLUSION(S)

Age does not alter the effects of diabetes-induced free radical damage in testis tissue; improvement in this damage can be achieved by vitamin E treatment.

Diabetes mellitus and serum carotenoids: findings of a population-based study in Queensland, Australia

BACKGROUND

Epidemiologic evidence suggests that serum carotenoids are potent antioxidants and may play a protective role in the development of chronic diseases including cancers, cardiovascular disease, and inflammatory diseases. The role of these antioxidants in the pathogenesis of diabetes mellitus remains unclear.

OBJECTIVE

This study examined data from a cross-sectional survey to investigate the association between serum carotenoids and type 2 diabetes.

DESIGN

Study participants were adults aged > or = 25 y (n = 1597) from 6 randomly selected cities and towns in Queensland, Australia. Study examinations conducted between October and December 2000 included fasting plasma glucose, an oral-glucose-tolerance test, and measurement of the serum concentrations of 5 carotenoid compounds.

RESULTS

Mean 2-h postload plasma glucose and fasting insulin concentrations decreased significantly with increasing quintiles of the 5 serum carotenoids--alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin, and lycopene. Geometric mean concentrations for all serum carotenoids decreased (all decreases were significant except that of lycopene) with declining glucose tolerance status. Beta-carotene had the greatest decrease, to geometric means of 0.59, 0.50, and 0.42 micromol/L in persons with normal glucose tolerance, impaired glucose metabolism, and type 2 diabetes, respectively (P < 0.01 for linear trend), after control for potential confounders.

CONCLUSIONS

Serum carotenoids are inversely associated with type 2 diabetes and impaired glucose metabolism. Randomized trials of diets high in carotenoid-rich vegetables and fruit are needed to confirm these results and those from other observational studies. Such evidence would have very important implications for the prevention of diabetes.

Oxidative stress as a therapeutic target in diabetes: revisiting the controversy

Oxidative stress has been repetitively shown to be a hallmark of many diseases linked with metabolic or vascular disorders. Therefore diabetes represents an ideal candidate for studying the consequences of oxidative stress and its treatment. Indeed diabetes constitutes a multiple source of free radicals, starting very early in the disease process and worsening over the course of disease. In view of the typical characteristics of diabetes, oxidative stress is expected to have a double impact, on both metabolic and vascular functions. It is therefore particularly disappointing to note the dramatic failure of clinical trials with antioxidants, although it must be pointed out that such studies have not been performed with only diabetic patients. This review describes the many different aspects of oxidative stress in diabetes and proposes possible explanations for the apparent lack of efficacy of antioxidant treatments in patients. Some verifications seem warranted before a definitive conclusion can be drawn about the validity of this therapeutic concept.

Serum nutritional status of tocopherol and retinol normalized to lipids of persons living in the southern rural Terai region in Nepal

OBJECTIVE

The present study examined the levels of serum α-Tocopherol (Toc), retinol (Ret), cholesterol (Chol) and triglycerides (TG), and their correlations in the sera of people in Nepal.

METHODS

The survey was conducted on the general populace in the agricultural Terai region in southern Nepal. The study population consisted of 93 males and 83 females aged 10-68 years. Serum Toc and Ret were measured by high-performance liquid chromatography.

RESULTS

No significant differences were observed between the genders for the average of total Chol (T-Chol) (140 and 145 mg/100 ml, respectively), HDL-C (45 and 47 mg/100 ml), LDL-C (94 and 97 mg/100 ml), and TG (106 and 110 mg/100 ml), and the ratio of LDL/HDL (2.16). The levels of mean Toc (4.32 and 4.27 μg/ml) were about the same for both genders, while the mean Ret levels were significantly higher for males (624 ng/ml) than for females (535 ng/ml) (p<0.001). A direct relationship was found between the levels of Toc and Ret (r=0.46, p<0.001 and r=0.28, p<0.05 for males and females, respectively). Serum levels of Toc and Ret were positively related to the levels of Chol (r=0.48 and r=0.58, p<0.001 for males and r=0.49, p<0.01 and r-0.28, p<0.05 for females, respectively). The ratio of Toc/TG normalized to serum TG was directly correlated to the ratio of Ret/TG (r=0.79 for males, and r=0.72 for females, p<0.001, respectively) and the ratios of Toc/TG and Ret/TG were negatively related to the LDL/HDL levels (r=-0.49 and r=-0.43, for males, and r=-0.46 and r=-0.57 for females, p<0.001, respectively).

CONCLUSION

The levels of Toc and Ret were low in the sera of people living in the southern rural Terai region in Nepal, and it was found that lower levels of Toc and Ret normalized to TG increased the ratio of LDL/HDL. These results suggest that greater intake of foods rich in Toc and Ret should be encouraged to reduce the erisk of coronary heart disease.