Application of probabilistic methods to address variability and uncertainty in estimating risks for non-cancer health effects.

Human health risk assessment currently uses the reference dose or reference concentration (RfD, RfC) approach to describe the level of exposure to chemical hazards without appreciable risk for non-cancer health effects in people. However, this "bright line" approach assumes that there is minimal risk below the RfD/RfC with some undefined level of increased risk at exposures above the RfD/RfC and has limited utility for decision-making. Rather than this dichotomous approach, non-cancer risk assessment can benefit from incorporating probabilistic methods to estimate the amount of risk across a wide range of exposures and define a risk-specific dose. We identify and review existing approaches for conducting probabilistic non-cancer risk assessments. Using perchloroethylene (PCE), a priority chemical for the U.S. Environmental Protection Agency under the Toxic Substances Control Act, we calculate risk-specific doses for the effects on cognitive deficits using probabilistic risk assessment approaches. Our probabilistic risk assessment shows that chronic exposure to 0.004 ppm PCE is associated with approximately 1-in-1,000 risk for a 5% reduced performance on the Wechsler Memory Scale Visual Reproduction subtest with 95% confidence. This exposure level associated with a 1-in-1000 risk for non-cancer neurocognitive deficits is lower than the current RfC for PCE of 0.0059 ppm, which is based on standard point of departure and uncertainty factor approaches for the same neurotoxic effects in occupationally exposed adults. We found that the population-level risk of cognitive deficit (indicating central nervous system dysfunction) is estimated to be greater than the cancer risk level of 1-in-100,000 at a similar chronic exposure level. The extension of toxicological endpoints to more clinically relevant endpoints, along with consideration of magnitude and severity of effect, will help in the selection of acceptable risk targets for non-cancer effects. We find that probabilistic approaches can 1) provide greater context to existing RfDs and RfCs by describing the probability of effect across a range of exposure levels including the RfD/RfC in a diverse population for a given magnitude of effect and confidence level, 2) relate effects of chemical exposures to clinical disease risk so that the resulting risk assessments can better inform decision-makers and benefit-cost analysis, and 3) better reflect the underlying biology and uncertainties of population risks.

A science-based agenda for health-protective chemical assessments and decisions: overview and consensus statement.

The manufacture and production of industrial chemicals continues to increase, with hundreds of thousands of chemicals and chemical mixtures used worldwide, leading to widespread population exposures and resultant health impacts. Low-wealth communities and communities of color often bear disproportionate burdens of exposure and impact; all compounded by regulatory delays to the detriment of public health. Multiple authoritative bodies and scientific consensus groups have called for actions to prevent harmful exposures via improved policy approaches. We worked across multiple disciplines to develop consensus recommendations for health-protective, scientific approaches to reduce harmful chemical exposures, which can be applied to current US policies governing industrial chemicals and environmental pollutants. This consensus identifies five principles and scientific recommendations for improving how agencies like the US Environmental Protection Agency (EPA) approach and conduct hazard and risk assessment and risk management analyses: (1) the financial burden of data generation for any given chemical on (or to be introduced to) the market should be on the chemical producers that benefit from their production and use; (2) lack of data does not equate to lack of hazard, exposure, or risk; (3) populations at greater risk, including those that are more susceptible or more highly exposed, must be better identified and protected to account for their real-world risks; (4) hazard and risk assessments should not assume existence of a "safe" or "no-risk" level of chemical exposure in the diverse general population; and (5) hazard and risk assessments must evaluate and account for financial conflicts of interest in the body of evidence. While many of these recommendations focus specifically on the EPA, they are general principles for environmental health that could be adopted by any agency or entity engaged in exposure, hazard, and risk assessment. We also detail recommendations for four priority areas in companion papers (exposure assessment methods, human variability assessment, methods for quantifying non-cancer health outcomes, and a framework for defining chemical classes). These recommendations constitute key steps for improved evidence-based environmental health decision-making and public health protection.

Thalamic Gamma Aminobutyric Acid Level Changes in Major Depressive Disorder After a 12-Week Iyengar Yoga and Coherent Breathing Intervention.

Objective: To determine if a 12-week yoga intervention (YI) was associated with increased gamma aminobutyric acid (GABA) levels and decreased depressive symptoms in participants with major depressive disorder (MDD). Methods: Subjects were randomized to a high-dose group (HDG) of three YIs a week and a low-dose group (LDG) of two YIs a week. Thalamic GABA levels were obtained using magnetic resonance spectroscopy at Scan-1 before randomization. After the assigned 12-week intervention, Scan-2 was obtained, immediately followed by a YI and Scan-3. Beck Depression Inventory II (BDI-II) scores were obtained before Scan-1 and Scan-3. Settings/Location: Screenings and interventions occurred at the Boston University Medical Center. Imaging occurred at McLean Hospital. Subjects: Subjects met criteria for MDD. Intervention: Ninety minutes of Iyengar yoga and coherent breathing at five breaths per minute plus homework. Outcome measures: GABA levels and the BDI-II. Results: BDI-II scores improved significantly in both groups. GABA levels from Scan-1 to Scan-3 and from Scan-2 to Scan-3 were significantly increased in the LDG (n = 15) and showed a trend in the total cohort. Post hoc, participants were divided into two groups based on having an increase in GABA levels at Scan-2. Increases in Scan-2 GABA levels were observed in participants whose mean time between their last YI and Scan-2 was 3.93 ± 2.92 standard deviation (SD) days, but not in those whose mean time between their last YI and Scan-2 was 7.83 ± 6.88 SD. Conclusions: This study tentatively supports the hypothesis that one of the mechanisms through which yoga improves mood is by increasing the activity of the GABA system. The observed increase in GABA levels following a YI that was no longer observed 8 days after a YI suggests that the associated increase in GABA after a YI is time limited such that at least one YI a week may be necessary to maintain the elevated GABA levels.

Psychological Function, Iyengar Yoga, and Coherent Breathing: A Randomized Controlled Dosing Study.

BACKGROUND: Evidence suggests that yoga may be an effective treatment for major depressive disorder (MDD). Studies evaluating the "dosing" of yoga treatment and efficacy for MDD are needed. The goal of this study was to assess the effects of an intervention combining Iyengar yoga and coherent breathing in participants with MDD and determine the optimal intervention dose. METHODS: Thirty-two participants (18 to 65 y of age) diagnosed with MDD were randomized to a high-dose group (HDG) or a low-dose group (LDG) of yoga and coherent breathing for 12 weeks. The HDG (n=15) involved three 90-minute yoga classes and four 30-minute homework sessions per week. The LDG (n=15) involved two 90-minute yoga classes and three 30-minute homework sessions per week. Participants were evaluated at baseline, week 4, week 8, and week 12 with the following instruments: Positivity Self-Test, Spielberger State Anxiety Inventory, Patient Health Questionnaire-9, Pittsburgh Sleep Quality Index, and Exercise-induced Feeling Inventory. Data were analyzed using intent-to-treat methods. RESULTS: Significant improvements in all outcome measures were found for both groups, with acute and cumulative benefits. Although the HDG showed greater improvements on all scales, between-group differences did not reach significance, possibly due to lack of power because of the small sample size. Cumulative yoga minutes were correlated with improvement in outcome measures. LIMITATION: This dosing study did not include a non-yoga control. CONCLUSIONS: Improvement in psychological symptoms correlated with cumulative yoga practice. Both interventions reduced symptoms of depression and anxiety and increased feelings of positivity. The time commitment for yoga practice needs to be weighed against benefits when designing yoga interventions.

A randomized controlled dosing study of Iyengar yoga and coherent breathing for the treatment of major depressive disorder: Impact on suicidal ideation and safety findings.

BACKGROUND: Yoga interventions offer promise for the treatment of major depressive disorder (MDD), yet their safety and potential impact on suicidal ideation (SI) have not been well documented. This study evaluated the safety of a randomized controlled dose-finding trial of Iyengar yoga plus coherent breathing for individuals with MDD, as well as the potential effects of the intervention on SI without intent. METHODS: Participants with Beck Depression Inventory-II (BDI-II) scores ≥14 and a diagnosis of MDD (using DSM-IV criteria) were randomized to either a low dose group (LDG) or high dose group (HDG) and received a 12-week manualized intervention. The LDG included two 90-min yoga classes plus three 30-min homework sessions weekly. The HDG offered three 90-min classes plus four 30-min homework sessions weekly. RESULTS: Thirty-two individuals with MDD were randomized, of which 30 completed the protocol. At screening, SI without intent was endorsed on the BDI-II by 9 participants; after completing the intervention, 8 out of 9 reported resolution of SI. There were 17 adverse events possibly-related and 15 definitely-related to the intervention. The most common protocol-related adverse event was musculoskeletal pain, which resolved over the course of the study. CONCLUSIONS: The Iyengar yoga plus coherent breathing intervention was associated with the resolution of SI in 8 out of 9 participants, with mild side effects that were primarily musculoskeletal in nature. This preliminary evidence suggests that this intervention may reduce SI without intent and be safe for use in those with MDD.