1.
Cadmium exposure and risk of diabetes and prediabetes: A systematic review and dose-response meta-analysis.
Filippini, T, Wise, LA, Vinceti, M
Environment international. 2022;158:106920
-
-
-
-
Free full text
Plain language summary
Cadmium is a toxic metal released in the environment after both natural and anthropogenic activities, particularly in contaminated and industrial areas devoted to smelting and refining of metals, and the manufacturing of batteries, coatings, or plastics. Exposure to cadmium may occur through occupational activities, smoking, food, and air pollution. The aim of this study was to provide updated literature on cadmium exposure and the risk of both type 2 diabetes and prediabetes, and to model the shape of these associations using a dose response approach. This study is a systematic review and meta-analysis of forty-two studies. Diabetes was investigated as an outcome in thirty-one studies, prediabetes in four studies, and both diabetes and prediabetes in seven studies. Results show that higher cadmium exposure was associated with increased risks of both diabetes and prediabetes. Diabetes risk increased linearly in studies using urinary cadmium concentrations, while disease risk increased only at the highest exposure levels when assessed using blood concentrations. The analysis for prediabetes also showed a linear increase in risk from low exposure, with a flattening effect at higher urinary cadmium concentrations. Authors conclude that their findings add to the available evidence on potential adverse health effects of environmental exposure to cadmium.
Expert Review
Conflicts of interest:
None
Take Home Message:
- Cadmium exposure through diet, occupational exposure and smoking may increase the risk of type 2 diabetes in affected individuals.
Evidence Category:
-
X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
Background
Cadmium exposure might occur through occupational activities, food, air pollution, and smoking. Smokers, in particular, have higher blood cadmium concentrations than non-smokers. Food is the main transmission route for non-smokers, particularly cereals, vegetables, mollusks, and offal. Females and older adults are at a greater risk due to an increased risk of iron deficiency in these population groups, leading to increased absorption, as well as greater age-related bioaccumulation.
Furthermore, cadmium exposure has been associated with an increased risk of diabetes in a number of studies, as referenced in the present manuscript. However, the magnitude and shape of the correlation are uncertain.This systematic review and meta-analysis therefore investigates the relationship between exposure to cadmium and type 2 diabetes and prediabetes risk.
Methods
- The systematic review was conducted and reported in line with the PRISMA 2020 statement. Search strings related to the terms “cadmium” and “diabetes”, or “prediabetes state” in PubMed/MEDLINE, Web of Science and EMBASE databases were employed to search for relevant articles. Latest search date: 1 October 2021.
- Eligibility criteria included: studies evaluating cadmium exposure via biomarker levels with outcomes of interest being type 2 diabetes or prediabetes using WHO criteria and the American Diabetes Association; and reporting of relative risk estimates using the hazard ratio (HR), risk ratio (RR), or odds ratio (OR) with the corresponding 95% confidence interval (CIs). For inclusion in dose-response meta-analysis: reported effect estimates for all exposure categories along with dose in each category.
- Studies were assessed for risk of bias using theROBINS-E tool. Overall certainty of the evidence was assessed using the GRADE approach.
- The meta-analysis involved estimating RRs with corresponding 95% CIs from each study. Generalised least-squares regression with a random effects model and restricted maximum likelihood estimation were used. The highest versus lowest exposure categories were compared. The association between exposure and risk of diabetes or prediabetes was investigated using a one-stage dose-response meta-analysis. Sensitivity analyses were performed and heterogeneity between studies was assessed..
Results
- 42 eligible studies (case-control, cross-sectional, and cohort studies), ranging 65-34, 814 male and female adult participants, were identified investigating the association between cadmium exposure and risk of diabetes or prediabetes. Seven of the included studies were at overall high risk of bias; heterogeneity in the resulting meta-analyses was moderate to substantial. Sensitivity analyses indicated comparable results. Assessment with GRADE found no major inconsistency, indirectness or imprecision for either outcome.
- Comparing the highest versus lowest cadmium exposure concentrations associated with type 2 diabetes resulted in a RR of 1.24 (95% CI 0.96–1.59), RR 1.21 (CI 95% 1.00–1.45), and RR 1.47 (CI 95% 1.01–2.13) for blood, urinary, and toenail matrices, respectively. Concurrently, there was an elevated risk of prediabetes for cadmium levels in urine of RR 1.41 (95% CI: 1.15–1.73) and blood RR 1.38 (95% CI: 1.16–1.63), respectively.
- In the dose-response meta-analysis, a linear positive correlation between increasing urinary cadmium levels and diabetes risk was observed, with a RR 1.25 (95% CI 0.90–1.72) at concentration 2.0 µg/g of creatinine compared with no exposure. Conversely, for blood cadmium concentrations, the diabetes risk seemed to rise above 1 µg/L compared with no exposure. Moreover, prediabetes risk increased up to approximately 2 µg/g creatinine beyond which a plateau was reached with RR 1.40 (95% CI 1.12–1.76) at 2 µg/g creatinine.
- The meta-regression showed a negligible correlation between blood cadmium levels and diabetes risk. However, a positive yet imprecise association was found with increasing urinary cadmium concentrations. Similarly, no association was observed between blood cadmium concentrations and risk of prediabetes, whereas a positive relationship with urinary cadmium levels was observed. However, these findings were based on a limited cohort of studies.
Conclusions
- A positive linear correlation between cadmium concentration (measured in multiple matrices) and risk of both type 2 diabetes and prediabetes with a dose-response relationship (moderate-certainty evidence) were observed in this systematic review and meta-analysis. Diabetes risk increased linearly in studies using urinary cadmium concentrations, whereas disease risk increased only at the highest exposure levels when assessed using blood levels. The analysis for prediabetes also demonstrated a linear increase in risk from low exposure, which plateaued at higher urinary cadmium concentrations.
Clinical practice applications:
- To inform practitioners and clients of the risks of cadmium exposure in the diet, through occupational exposure, and through smoking.
- To motivate practitioners to educate themselves and their clients regarding the foods which may pose a higher risk of cadmium exposure (not reviewed in the present article).
- To advise clients on prediabetes and type 2 diabetes risk from cadmium exposure through smoking.
Considerations for future research:
- As cited by the authors, future studies could incorporate stratified analysis in specific subgroups, e.g., non-smokers, or could be restricted to prospective cohort studies with more sufficient data,
- Large-scale observational studies could be conducted investigating cadmium exposure in smokers versus non-smokers.
- Clinical trials could be performed to evaluate the effect of reduction or cessation of tobacco smoking on total body cadmium concentrations .
- Continuous surveillance of dietary cadmium exposure and other heavy metals should be prioritised to inform public health.
- Dietary interventions could assess the possibility to attenuate the risk of cadmium exposure.
Abstract
BACKGROUND Cadmium exposure has been associated with increased diabetes risk in several studies, though there is still considerable debate about the magnitude and shape of the association. OBJECTIVE To perform a systematic review and meta-analysis of observational studies investigating the relation between cadmium exposure and risk of type 2 diabetes and prediabetes, and to summarize data on the magnitude and shape of the association. DATA SOURCE After conducting an online literature search through October 1, 2021, we identified 42 eligible studies investigating the association between cadmium exposure and risk of diabetes and prediabetes. STUDY ELIGIBILITY CRITERIA We included studies that assessed cadmium exposure through biomarker levels; examined type 2 diabetes or prediabetes among outcomes; and reported effect estimates for cadmium exposure for meta-analysis only. STUDY APPRAISAL AND SYNTHESIS METHODS Studies were evaluated using ROBINS-E risk of bias tool. We quantitively assessed the relation between exposure and study outcomes using one-stage dose-response meta-analysis with a random effects meta-analytical model. RESULTS In the meta-analysis, comparing highest-versus-lowest cadmium exposure levels, summary relative risks (RRs) for type 2 diabetes were 1.24 (95% confidence interval 0.96-1.59), 1.21 (1.00-1.45), and 1.47 (1.01-2.13) for blood, urinary, and toenail matrices, respectively. Similarly, there was an increased risk of prediabetes for cadmium concentrations in both urine (RR = 1.41, 95% CI: 1.15-1.73) and blood (RR = 1.38, 95% CI: 1.16-1.63). In the dose-response meta-analysis, we observed a consistent linear positive association between cadmium exposure and diabetes risk, with RRs of 1.25 (0.90-1.72) at 2.0 µg/g of creatinine. Conversely for blood cadmium, diabetes risk appeared to increase only above 1 µg/L. Prediabetes risk increased up to approximately 2 µg/g creatinine above which it reached a plateau with RR of 1.42 (1.12-1.76) at 2 µg/g creatinine. LIMITATIONS AND CONCLUSIONS This analysis provides moderate-certainty evidence for a positive association between cadmium exposure (measured in multiple matrices) and risk of both diabetes and prediabetes.
2.
Effects of Lactococcus lactis subsp. cremoris YRC3780 daily intake on the HPA axis response to acute psychological stress in healthy Japanese men.
Matsuura, N, Motoshima, H, Uchida, K, Yamanaka, Y
European journal of clinical nutrition. 2022;76(4):574-580
-
-
-
-
Free full text
-
Plain language summary
The hypothalamic-pituitary-adrenal (HPA) axis is involved in the stress response and is linked to the microbiome through a number of possible mechanisms, including immune-related ones. Lactococcus lactis subsp. cremoris YRC3780 (YRC3780), a probiotic isolated from kefir, has been shown to have beneficial immune-modulatory properties. The aim of this double-blind, placebo-controlled trial, which included 27 healthy young men, was to assess sleep quality, mental health, HPA axis activity (salivary cortisol) and response to an acute stress test during/after 8 weeks of supplementation with YRC3780. At 8 weeks, salivary morning cortisol levels were significantly reduced in the probiotic compared to the placebo group. The effect on the stress test depended on whether or not participants were considered “cortisol-responders” or not. Improvements in sleep quality were seen at 6 weeks (but not at any other time points) in 1 out of 2 sleep questionnaires in the YRC3780 group, whilst no significant differences were observed in actigraphy-measured sleep efficiency. There were no differences in mood between groups, but significant improvements in general health in the probiotic group. Interestingly, no changes in the microbiome of the probiotic group were seen, suggesting that the observed effects may be mediated via the immune system.
Expert Review
Conflicts of interest:
None
Take Home Message:
- Research indicates a bidirectional interaction between the gut microbiome and the central nervous system, affecting the functions of the brain and spinal cord.
- This clinical trial suggests that daily intake of Lactococcus lactis subsp. cremoris (YRC3780) may enhance the HPA axis response to acute psychological stress, potentially linked to a reduction in morning cortisol levels.
Evidence Category:
-
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
X
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
Introduction
A randomized, placebo-controlled, double-blind clinical trial was conducted to investigate the influence of Lactococcus lactis subsp. cremoris (YRC3780), isolated from kefir, on stress response, sleep quality, and mental health.
Method
Twenty-seven healthy young men, with an average age of 23.5 years, and mean body mass index of 21.5 kg/m2 , were randomly assigned to either the YRC3780 group or the placebo group. Participants were administered YRC3780 or a placebo daily for 8 weeks.
Throughout the study, participants completed assessments, including the Athens Insomnia Scale (AIS), the Pittsburgh Sleep Quality Index (PSQI), the General Health Questionnaire (GHQ-28), and the Profile of Mood States 2nd Edition-Adult Short, Total Mood Disturbance subscale (POMS 2 TMD), every 2 weeks. Additionally, diurnal rhythms of HPA axis activity were assessed every 2 weeks through saliva samples collected at 2-hour intervals during the day. At the end of the 8-week supplementation period, participants underwent the Trier Social Stress Test (TSST) to evaluate the effects of daily YRC3780 intake on the HPA axis stress response. In addition, three fecal samples were collected to analyse the gut microbiome (on the last day of baseline, and at 4 and 8 weeks).
A total of 27 out of 33 subjects (81%) completed the study, with six participants withdrawing without providing explanations.
Results
The primary findings of this study were as follows:
- At week 6 of YRC3780 supplementation, salivary cortisol levels at 2 hours and 6 hours after waking were significantly lower in the YRC3780 group compared to the placebo group (p=0.05).
- Salivary cortisol concentrations at 40 minutes after the TSST were significantly lower in the YRC3780 group (4.2 ± 4.4 nmol/L, mean ± SD) than in the placebo group (7.6 ± 4.7 nmol/L) (p=0.043).
- AIS scores at 6 weeks and GHQ-28 scores at 8 weeks were significantly lower in the YRC3780 group compared to the placebo group (AIS, p=0.031; GHQ-28, p=0.038) indicating better sleep quality and a better mental state.
Conclusion:
Oral supplementation with YRC3780 may have beneficial effects on the HPA axis response to acute psychological stress, potentially associated with a decrease in morning cortisol levels. Additionally, the study suggests that the lower basal activity and stress reactivity of the HPA axis may lead to improvements in subjective sleep quality and mental health.
Clinical practice applications:
- The precise mechanisms underlying the correlation between the gut microbiota and the gut-brain axis remain incompletely understood, emphasising the need for further research.
- This clinical trial demonstrated that daily intake of YRC3780 decreased morning salivary cortisol levels at 6 and 8 weeks and reduced the salivary cortisol response to acute psychological stress.
Considerations for future research:
- Larger, adequately powered clinical trials are required to provide deeper insights into the mechanisms responsible for the stress-reducing and sleep-improving effects of Lactococcus lactis subsp. cremoris.
- Furthermore, investigations into optimal dosage and duration of probiotic supplementation are warranted for a more comprehensive understanding, particularly in diverse demographic groups.
- Comparative research is needed to explore the effects of various probiotic strains on objective stress responses.
Abstract
BACKGROUND Lactococcus lactis subsp. cremoris (YRC3780), which is isolated from kefir, has been associated with anti-allergic effects in humans. However, it remains unknown whether daily intake of YRC3780 attenuates the response to psychological stress in humans in parallel with changes to the gut microbiome. We examined the fundamental role of YRC3780 in the gut microbiome, stress response, sleep, and mental health in humans. METHODS Effects of daily intake of YRC3780 on the hypothalamic-pituitary-adrenal (HPA) axis response to acute psychological stress were investigated in a double-blind, placebo-controlled clinical trial involving 27 healthy young men (mean age and body mass index: 23.5 years and 21.5 kg/m2) who were randomly assigned to placebo (n = 13) or YRC3780 (n = 14) groups. The HPA axis response to acute psychological stress, the diurnal rhythm of HPA axis activity, and gut microbiome were assessed and compared between the two groups. RESULTS The results showed that daily intake of YRC3780 significantly lowered morning salivary cortisol levels compared with placebo. In addition, salivary cortisol levels following a social stress test significantly decreased +40 min after beginning the TSST in the YRC3780-treated group compared to placebo. There were no significant differences between the two groups in terms of actigraphy-based sleep quality, but the subjective sleep quality and mental health were significantly improved in the YRC3780-treated group compared to placebo. CONCLUSIONS Our study suggests that daily intake of YRC3780 improves the HPA axis response to acute psychological stress, which might be associated with a decrease in morning cortisol levels.