Exposure to environmental factors in drinking water: risk of islet autoimmunity and type 1 diabetes--the BABYDIAB study

Dietary nitrate, nitrite, and nitrosamine in association with diabetes: a systematic review and meta-analysis

CONTEXT

Diabetes is a global health concern, and diet is a contributing factor to diabetes. Findings regarding the connection between nitrate, nitrite, and nitrosamine and diabetes risk are inconsistent.

OBJECTIVE

The aim was to examine the effects of these dietary compounds on diabetes risk.

DATA SOURCES

The data were sourced from PubMed, EMBASE, Scopus, and Web of Science until February 28, 2023. Studies that reported individual-level consumption of these compounds were included. Review articles or ecological studies were excluded.

DATA EXTRACTION

The number of events and total observations were recorded.

DATA ANALYSIS

The pooled odds ratio (OR) was calculated and displayed in a forest plot. Subgroup and sensitivity analyses were predefined. A dose-response meta-analysis was conducted to determine the exposure intervals that may increase the risk of disease. Six observational reports that met the inclusion criteria were included, involving 108 615 individuals. Participants in the highest quantile of nitrite intake had a greater risk of diabetes compared with those in the lowest quantile (OR, 1.61; 95% confidence interval [CI], 1.08-2.39; I2 = 74%, P = 0.02). Higher nitrosamine consumption tended to increase diabetes risk (OR, 1.52; 95% CI, 0.76-3.04; I2 = 76%; P = 0.24). The relationship was stronger for type 1 (OR, 1.79; 95% CI, 1.20-2.67; I2 = 58%; P < 0.01) than for type 2 diabetes (OR, 1.42; 95% CI, 0.86-2.37; I2 = 71%; P = 0.17). Additionally, nitrite consumption had a dose-dependent association with both phenotypes. No association was found between diabetes risk and high nitrate intake (OR, 1.01; 95% CI, 0.87-1.18; I2 = 28%; P = 0.87).

CONCLUSION

Attention should be paid to the consumption of nitrite-containing foods.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42023394462 (https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=394462).

Metabolic effects of L-citrulline in type 2 diabetes

The prevalence of type 2 diabetes (T2D) is increasing worldwide. Decreased nitric oxide (NO) bioavailability is involved in the pathophysiology of T2D and its complications. L-citrulline (Cit), a precursor of NO production, has been suggested as a novel therapeutic agent for T2D. Available data from human and animal studies indicate that Cit supplementation in T2D increases circulating levels of Cit and L-arginine while decreasing circulating glucose and free fatty acids and improving dyslipidemia. The underlying mechanisms for these beneficial effects of Cit include increased insulin secretion from the pancreatic β cells, increased glucose uptake by the skeletal muscle, as well as increased lipolysis and β-oxidation, and decreased glyceroneogenesis in the adipose tissue. Thus, Cit has antihyperglycemic, antidyslipidemic, and antioxidant effects and has the potential to be used as a new therapeutic agent in the management of T2D. This review summarizes available literature from human and animal studies to explore the effects of Cit on metabolic parameters in T2D. It also discusses the possible mechanisms underlying Cit-induced improved metabolic parameters in T2D.

Association of Maternal Dietary Components During Pregnancy and/or Lactation with Insulin-Dependent Diabetes Mellitus

CONTEXT

Considering the increasing trend in the incidence of type 1 diabetes mellitus (T1DM), the identification of its environmental determinants, especially those related to the prenatal and lactation period, might ultimately result in primary prevention of the disease. We aimed to review the evidence of the association between mothers' dietary components during pregnancy and/or lactation with T1DM.

EVIDENCE ACQUISITION

An electronic and comprehensive literature search was performed until August 2019 in the international databases, including Web of Science (ISI), PubMed, and Scopus, using the following keywords: type 1 diabetes mellitus, autoimmunity, mother, maternal, diet and lactation in different combinations. Papers related to the objectives of the study were selected.

RESULTS

Based on our review, the maternal consumption of meat, especially processed meat, was associated with increased risk of T1DM, whereas the maternal use of vegetables, potato, low-fat margarine, and berries showed protective effects against the development of T1DM in offspring. There was no significant association between the use of multivitamins and mineral supplements with T1DM, according to the available data. The results of the reviewed studies regarding the association between the maternal use of vitamin D, fatty acids, and coffee during pregnancy with T1DM were not consistent and conclusive.

CONCLUSIONS

Findings of this review indicate that the maternal consumption of some foods is associated with increased or decreased risk of T1DM. However, for some foods or dietary components, including coffee, vitamin D, and fatty acids, the results are not conclusive. We conclude that although maternal diet could influence the development of insulin autoantibodies (IA) and T1DM in offspring, there is no sufficient evidence for most nutrients, and available data are controversial, which should be dealt with in future cohort or interventional studies.

Toxic metals in cord blood and later development of Type 1 diabetes

The incidence of type 1 diabetes (T1D) has increased explained by changes in environment or lifestyle. In modern society dissemination of heavy metals has increased. As the autoimmune process usually starts already, we hypothesized that exposure to toxic metals during fetal life might contribute to development of T1D in children.

We analysed arsenic (AS), aluminium (Al), cadmium (Cd), lithium (Li), mercury (Hg), lead (Pb), in cord blood of 20 children who later developed T1D (probands), and in 40 age-and sex-matched controls. Analysis of heavy metals in cord blood was performed by ALS Scandinavia AB (Luleå, Sweden) using the ‘ultrasensitive inductively coupled plasma sector field mass spectrometry method’ (ICP-SFMS) after acid digestion with HNO₃.

Most children had no increased concentrations of the metals in cord blood. However, children who later developed T1D had more often increased concentrations (above limit of detection; LOD) of aluminium (p = 0.006) in cord blood than the non-diabetic controls, and also more often mercury and arsenic (n.s).

Our conclusion is that exposure to toxic metals during pregnancy might be one among several contributing environmental factors to the disease process if confirmed in other birth cohort trials.

Maternal and Early Life Iron Intake and Risk of Childhood Type 1 Diabetes: A Danish Case-Cohort Study

Background: Iron overload has been associated with diabetes. Studies on iron exposure during pregnancy and in early life and risk of childhood type 1 diabetes (T1D) are sparse. We investigated whether iron supplementation during pregnancy and early in life were associated with risk of childhood T1D. Methods: In a case-cohort design, we identified up to 257 children with T1D (prevalence 0.37%) from the Danish National Birth Cohort through linkage with the Danish Childhood Diabetes Register. The primary exposure was maternal pure iron supplementation (yes/no) during pregnancy as reported in interview two at 30 weeks of gestation (n = 68,497 with iron supplement data). We estimated hazard ratios (HRs) using weighted Cox regression adjusting for multiple confounders. We also examined if offspring supplementation during the first 18 months of life was associated with later risk of T1D. Results: Maternal iron supplementation was not associated with later risk of T1D in the offspring HR 1.05 (95% CI: 0.76–1.45). Offspring intake of iron droplets during the first 18 months of life was inversely associated with risk of T1D HR 0.74 (95% CI: 0.55–1.00) (p_trend = 0.03). Conclusions: Our large-scale prospective study demonstrated no harmful effects of iron supplementation during pregnancy and in early life in regard to later risk of childhood T1D in the offspring.

Drinking Water Nitrate and Human Health: An Updated Review

Nitrate levels in our water resources have increased in many areas of the world largely due to applications of inorganic fertilizer and animal manure in agricultural areas. The regulatory limit for nitrate in public drinking water supplies was set to protect against infant methemoglobinemia, but other health effects were not considered. Risk of specific cancers and birth defects may be increased when nitrate is ingested under conditions that increase formation of N-nitroso compounds. We previously reviewed epidemiologic studies before 2005 of nitrate intake from drinking water and cancer, adverse reproductive outcomes and other health effects. Since that review, more than 30 epidemiologic studies have evaluated drinking water nitrate and these outcomes. The most common endpoints studied were colorectal cancer, bladder, and breast cancer (three studies each), and thyroid disease (four studies). Considering all studies, the strongest evidence for a relationship between drinking water nitrate ingestion and adverse health outcomes (besides methemoglobinemia) is for colorectal cancer, thyroid disease, and neural tube defects. Many studies observed increased risk with ingestion of water nitrate levels that were below regulatory limits. Future studies of these and other health outcomes should include improved exposure assessment and accurate characterization of individual factors that affect endogenous nitrosation.

The Role of Iron in Type 1 Diabetes Etiology: A Systematic Review of New Evidence on a Long-Standing Mystery

BACKGROUND

The incidence of type 1 diabetes (T1D) is rising, which might be due to the influence of environmental factors. Biological and epidemiological evidence has shown that excess iron is associated with beta-cell damage and impaired insulin secretion.

AIM

In this review, our aim was to assess the association between iron and the risk of T1D.

METHODS

A systematic literature search was performed in PubMed and EMBASE in July 2016. Studies investigating the effect of iron status/intake on the risk of developing T1D later were included, and study quality was evaluated. The results have been summarized in narrative form.

RESULTS

From a total of 931 studies screened, we included 4 observational studies evaluating iron intake from drinking water or food during early life and the risk of T1D. The quality of the studies was moderate to high assessed via the nine-star Newcastle Ottawa Scale. One out of the four studies included in this review found estimates of dietary iron intake to be associated with risk of T1D development, whereas three studies found no such relationship for estimates of iron in drinking water.

CONCLUSIONS

The limited number of studies included found dietary iron, but not iron in drinking water, to be associated with risk of T1D. Further studies are needed to clarify the association between iron and risk of T1D, especially studies including measurements of body iron status.

Nitrate-nitrite-nitrosamines exposure and the risk of type 1 diabetes: A review of current data

The potential toxic effects of nitrate-nitrite-nitrosamine on pancreatic β cell have remained a controversial issue over the past two decades. In this study, we reviewed epidemiological studies investigated the associations between nitrate-nitrite-nitrosamines exposure, from both diet and drinking water to ascertain whether these compounds may contribute to development of type 1 diabetes. To identify relevant studies, a systematic search strategy of PubMed, Scopus, and Science Direct was conducted using queries including the key words “nitrate”, “nitrite”, “nitrosamine” with “type 1 diabetes” or “insulin dependent diabetes mellitus”. All searches were limited to studies published in English. Ecologic surveys, case-control and cohort studies have indicated conflicting results in relation to nitrate-nitrite exposure from drinking water and the risk of type 1 diabetes. A null, sometimes even negative association has been mainly reported in regions with a mean nitrate levels < 25 mg/L in drinking water, while increased risk of type 1 diabetes was observed in those with a maximum nitrate levels > 40-80 mg/L. Limited data are available regarding the potential diabetogenic effect of nitrite from drinking water, although there is evidence indicating dietary nitrite could be a risk factor for development of type 1 diabetes, an effect however that seems to be significant in a higher range of acceptable limit for nitrate/nitrite. Current data regarding dietary exposure of nitrosamine and development of type 1 diabetes is also inconsistent. Considering to an increasing trend of type 1 diabetes mellitus (T1DM) along with an elevated nitrate-nitrite exposure, additional research is critical to clarify potential harmful effects of nitrate-nitrite-nitrosamine exposure on β-cell autoimmunity and the risk of T1DM.

Environmental risk factors for type 1 diabetes

The incidence of type 1 diabetes has risen considerably in the past 30 years due to changes in the environment that have been only partially identified. In this Series paper, we critically discuss candidate triggers of islet autoimmunity and factors thought to promote progression from autoimmunity to overt type 1 diabetes. We revisit previously proposed hypotheses to explain the growth in the incidence of type 1 diabetes in light of current data. Finally, we suggest a unified model in which immune tolerance to β cells can be broken by several environmental exposures that induce generation of hybrid peptides acting as neoautoantigens.

Beneficial effects of inorganic nitrate/nitrite in type 2 diabetes and its complications

Background and aim

The ability of inorganic nitrate and nitrite to convert to nitric oxide (NO), and some of its properties e.g. regulation of glucose metabolism, vascular homeostasis, and insulin signaling pathway, have recently raised the hypothesis that inorganic nitrate and nitrite could be potential therapeutic agents in type 2 diabetes. In this review, we reviewed experimental and clinical studies investigating the effect of nitrate/nitrite administration on various aspects of type 2 diabetes.

Findings

Studies showed that an altered metabolism of nitrate/nitrite and impaired NO pathway occurs in diabetes which could contribute to its complications. Some important beneficial properties, including regulation of glucose homeostasis and insulin signaling pathway, improvement of insulin resistance and vascular function, hypotensive, hypolipidemic as well as anti-inflammatory and anti-oxidative effects have been observed following administration of inorganic nitrate/nitrite.

Conclusion

It seems that dietary nitrate/nitrite could be a compensatory fuel for a disrupted nitrate/nitrite/NO pathway and related disorders in diabetes. Although some beneficial properties of nitrate/nitrite have been reported by experimental investigations, long-term clinical studies with various doses of inorganic nitrate/nitrite supplementation, are recommended to confirm these effects.

Can exposure to environmental chemicals increase the risk of diabetes type 1 development?

Type 1 diabetes mellitus (T1DM) is an autoimmune disease, where destruction of beta-cells causes insulin deficiency. The incidence of T1DM has increased in the last decades and cannot entirely be explained by genetic predisposition. Several environmental factors are suggested to promote T1DM, like early childhood enteroviral infections and nutritional factors, but the evidence is inconclusive. Prenatal and early life exposure to environmental pollutants like phthalates, bisphenol A, perfluorinated compounds, PCBs, dioxins, toxicants, and air pollutants can have negative effects on the developing immune system, resulting in asthma-like symptoms and increased susceptibility to childhood infections. In this review the associations between environmental chemical exposure and T1DM development is summarized. Although information on environmental chemicals as possible triggers for T1DM is sparse, we conclude that it is plausible that environmental chemicals can contribute to T1DM development via impaired pancreatic beta-cell and immune-cell functions and immunomodulation. Several environmental factors and chemicals could act together to trigger T1DM development in genetically susceptible individuals, possibly via hormonal or epigenetic alterations. Further observational T1DM cohort studies and animal exposure experiments are encouraged.

Environmental trigger(s) of type 1 diabetes: why so difficult to identify?

Type 1 diabetes (T1D) is one of the most common chronic diseases with childhood onset, and the disease has increased two- to fivefold over the past half century by as yet unknown means. T1D occurs when the body's immune system turns against itself so that, in a very specific and targeted way, it destroys the pancreatic β-cells. T1D results from poorly defined interactions between susceptibility genes and environmental determinants. In contrast to the rapid progress in finding T1D genes, identification and confirmation of environmental determinants remain a formidable challenge. This review article will focus on factors which have to be evaluated and decision to take before starting a new prospective cohort study. Considering all the large ongoing prospective studies, new and more conclusive data than that obtained so far should instead come from international collaboration on the ongoing cohort studies.

Modulation of the pancreatic islet-stress axis as a novel potential therapeutic target in diabetes mellitus

Loss of pancreatic islet function and insulin-producing beta cell mass is a central hallmark in the pathogenesis of both type 1 and type 2 diabetes. While in type 1 diabetes this phenomenon is due to an extensive destruction of beta cells caused by an autoimmune process, the mechanisms resulting in beta cell failure in type 2 diabetes are different and less clear. Also, beta cell destruction in type 1 diabetes occurs early and is the initial step in the pathogenetic process, while beta cell loss in type 2 diabetes after an initial phase of hyperinsulinemia due to the underlying insulin resistance occurs relatively late and it is less pronounced. Since diabetes mellitus is the most frequent endocrine disease, with an increasing high prevalence worldwide, huge efforts have been made over the past many decades to identify predisposing genetic, environmental, and nutritional factors in order to develop effective strategies to prevent the disease. In parallel, extensive studies in different cell systems and animal models have helped to elucidate our understanding of the physiologic function of islets and to gain insight into the immunological and non-immunological mechanisms of beta cell destruction and failure. Furthermore, currently emerging concepts of beta cell regeneration (e.g., the restoration of the beta cell pool by regenerative, proliferative and antiapoptotic processes, and recovery of physiologic islet function) apparently is yielding the first promising results. Recent insights into the complex endocrine and paracrine mechanisms regulating the physiologic function of pancreatic islets, as well as beta cell life and death, constitute an essential part of this new and exciting area of diabetology. For example, understanding of the physiological role of glucagon-like peptide 1 has resulted in the successful clinical implementation of incretin-based therapies over the last years. Further, recent data suggesting paracrine effects of growth hormone-releasing hormone and corticotropin-releasing hormone on the regulation of pancreatic islet function, survival, and proliferation as well as on local glucocorticoid metabolism provide evidence for a potential role of the pancreatic islet-stress axis in the pathophysiology of diabetes mellitus. In this chapter, we provide a comprehensive overview of current preventive and regenerative concepts as a basis for the development of novel therapeutic approaches to the treatment of diabetes mellitus. A particular focus is given on the potential of the pancreatic islet-stress axis in the development of novel regenerative strategies.

Low zinc in drinking water is associated with the risk of type 1 diabetes in children

AIM

To explore if drinking water may influence the development of type 1 diabetes in children, either via enterovirus spread via drinking water or quality of drinking water related to acidity or concentration of certain minerals.

METHODS

One hundred and forty-two families with a child with diabetes and who lived either in seven municipalities with a high annual diabetes incidence during 1977-2001 and in six municipalities with the lowest incidence during those 25 yr were asked to participate. Three hundred and seventy-three families in these communities were used as controls. The families filled a 200-mL plastic bottle with their tap drinking water and returned it by mail. The water samples were analyzed for pH, zinc, iron, nitrate, nitrite, nitrate-nitrogen and nitrite-nitrogen, and occurrence of enterovirus RNA.

RESULTS

Enterovirus RNA was not found in the tap water samples. The concentration of zinc, nitrate, and nitrate-nitrogen was lower in the municipalities with high incidence of type 1 diabetes. The water samples from families with a child with diabetes had lower concentration of zinc than water samples from control families.

CONCLUSION

Low zinc in drinking water is associated with the risk of developing type 1 diabetes during childhood. Enterovirus does not seem to be spread via drinking water in a country with modern water works.

Water quality monitoring records for estimating tap water arsenic and nitrate: a validation study

BACKGROUND

Tap water may be an important source of exposure to arsenic and nitrate. Obtaining and analyzing samples in the context of large studies of health effects can be expensive. As an alternative, studies might estimate contaminant levels in individual homes by using publicly available water quality monitoring records, either alone or in combination with geographic information systems (GIS).

METHODS

We examined the validity of records-based methods in Washington State, where arsenic and nitrate contamination is prevalent but generally observed at modest levels. Laboratory analysis of samples from 107 homes (median 0.6 microg/L arsenic, median 0.4 mg/L nitrate as nitrogen) served as our "gold standard." Using Spearman's rho we compared these measures to estimates obtained using only the homes' street addresses and recent and/or historical measures from publicly monitored water sources within specified distances (radii) ranging from one half mile to 10 miles.

RESULTS

Agreement improved as distance decreased, but the proportion of homes for which we could estimate summary measures also decreased. When including all homes, agreement was 0.05-0.24 for arsenic (8 miles), and 0.31-0.33 for nitrate (6 miles). Focusing on the closest source yielded little improvement. Agreement was greatest among homes with private wells. For homes on a water system, agreement improved considerably if we included only sources serving the relevant system (rho = 0.29 for arsenic, rho = 0.60 for nitrate).

CONCLUSIONS

Historical water quality databases show some promise for categorizing epidemiologic study participants in terms of relative tap water nitrate levels. Nonetheless, such records-based methods must be used with caution, and their use for arsenic may be limited.

An update on preventive and regenerative therapies in diabetes mellitus

Type 1A (immune-mediated) and type 2 diabetes mellitus are two of the most common severe chronic illnesses, affecting over 230 million people worldwide with an estimated global prevalence of 5.1%. Although type 1 and type 2 diabetes differ greatly in modes of pathogenesis, these illnesses share a common pathology and consequences characterized by loss of functional beta-cell mass and subsequent dysregulation of carbohydrate and lipid metabolism. Since therapy for diabetes and the associated complications poses enormous public health and economic burdens, novel preventive and regenerative therapies have emerged in the past decade with the aim to preserve beta-cell mass and delay the onset of diabetes. The goal of this review is to provide a comprehensive overview of current efforts in the fight against diabetes, and attempts to document all strategies that have emerged in clinical studies within the past 25 years. First, strategies to identify individuals at risk, ranging from whole-genome scans to autoantibody screening, will be discussed. Second, novel approaches to prevent or delay the onset of disease will be covered. Particular focus is given on emerging strategies for individuals at risk for type 1 diabetes that target T-cell regulation and induction of tolerance, while new pharmaceutical concepts in combination with lifestyle interventions are discussed within the scope of type 2 diabetes prevention. Lastly, important efforts to halt disease progression with emphasis on beta-cell regeneration are presented.