Are U-shaped relationships between risk factors and outcomes artifactual?

BACKGROUND

The objective of this study was to evaluate whether the observed nadir in a U- or J-shaped relationship between a particular risk factor and a future health outcome is a function of the distribution of the risk factor in the sample being analyzed.

METHODS

Data from the ORIGIN trial were used to assess the relationship between three risk factors (weight, systolic blood pressure, and serum insulin) and the hazard of a major cardiovascular event comprising a nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death. Three spline curves were generated for each risk factor. The first was based on all available data, the second for a subgroup with a higher mean risk factor level, and the third for a subgroup with a lower mean risk factor level. Nadir levels of the risk factor (i.e., risk factor levels predicting the lowest hazard) were then identified for each spline curve.

RESULTS

When compared to the nadir values based on all available data, nadir values for all three risk factors were higher for the subgroups with higher mean levels and lower for those with lower mean levels.

CONCLUSIONS

The distribution of a risk factor in the population is an important determinant of its nadir value. Populations with high or low values may have high and low nadirs, respectively. Identification of a nadir for a modifiable risk factor from epidemiologic relationships may therefore arise from this distribution bias and is therefore unrelated to therapeutic targets.

Using interview surveys and multispecies occupancy models to inform vertebrate conservation

Species distribution data are an essential biodiversity variable requiring robust monitoring to inform wildlife conservation. Yet, such data remain inherently sparse because of the logistical challenges of monitoring biodiversity across broad geographic extents. Surveys of people knowledgeable about the occurrence of wildlife provide an opportunity to evaluate species distributions and the ecology of wildlife communities across large spatial scales. We analyzed detection histories of 30 vertebrate species across the Western Ghats biodiversity hotspot in India, obtained from a large-scale interview survey of 2318 people who live and work in the forests of this region. We developed a multispecies occupancy model that simultaneously corrected for false-negative (non-detection) and false-positive (misidentification) errors that interview surveys can be prone to. Using this model, we integrated data across species in composite analyses of the responses of functional species groups (based on disturbance tolerance, diet, and body mass traits) to spatial variation in environmental variables, protection, and anthropogenic pressures. We observed a positive association between forest cover and the occurrence of species with low tolerance of human disturbance. Protected areas were associated with higher occurrence for species across different functional groups compared with unprotected lands. We also observed the occurrence of species with low disturbance tolerance, herbivores, and large-bodied species was negatively associated with developmental pressures, such as human settlements, energy production and mining, and demographic pressures, such as biological resource extraction. For the conservation of threatened vertebrates, our work underscores the importance of maintaining forest cover and reducing deforestation within and outside protected areas, respectively. In addition, mitigating a suite of pervasive human pressures is also crucial for wildlife conservation in one of the world's most densely populated biodiversity hotspots.

Relationship between creatinine to body weight ratios and diabetes mellitus: A Chinese cohort study

BACKGROUND

Research on the relationship between creatinine to body weight ratios (Cre/BW ratios) and the prevalence of diabetes is still lacking. The intention of this research was to explore the potential relationship between Cre/BW ratio and diabetes prevalence in Chinese adults.

METHODS

This retrospective study was conducted on 199 526 patients in the Chinese Rich Healthcare Group from 2010 to 2016. The participants were divided into four groups on the basis of the quartiles of the Cre/BW ratios. Multivariate multiple imputation and dummy variables were used to handle missing values. Multivariate regression analysis was applied to detect the relationship between Cre/BW and diabetes. A smoothing plot was also used to identify whether there were nonlinear relationships.

RESULTS

After handling missing values and adjusting for potential confounders, the multivariate Cox regression analysis results showed that Cre/BW was inversely correlated with diabetes risk (hazard ratio [HR]: 0.268; 95% confidence interval [CI]: 0.229-0.314, p < 0.00001). For men, the HR of incident diabetes was 0.255 (95% CI: 0.212-0.307) and for women it was 0.297 (95% CI: 0.218-0.406). Moreover, sensitivity analysis confirmed the stability of the results. Furthermore, the smoothing plot revealed that there was a saturation effect between Cre/BW and the incidence of diabetes.

CONCLUSIONS

This study demonstrated that increased Cre/BW is negatively correlated with diabetes in Chinese adults. It also found that Cre/BW has a nonlinear relationship with the incidence of diabetes.

Effect of baseline body mass index on glycemic control and weight change with exenatide monotherapy in Chinese drug-naïve type 2 diabetic patients

BACKGROUND

The weight-reducing effect of exenatide has been proved, but too much weight loss in normal-weight patients may concern physicians. This study evaluated the effects of exenatide monotherapy on glycemic control and weight change in normal-weight, overweight, and obese patients with newly diagnosed type 2 diabetes (T2D).

METHODS

In this multicenter prospective study, 29 normal-weight, 54 overweight, and 27 obese newly diagnosed and drug-naïve patients with T2D were treated with exenatide for 48 weeks. The primary efficacy endpoint was the effect of baseline body mass index (BMI) on glycemic control, measured as the change in HbA1c from baseline to Week 48 compared among different BMI groups. Other endpoints included comparisons of the effects of exenatide on fasting plasma glucose (FPG), postprandial plasma glucose (PPG), body weight, and other metabolic indices.

RESULTS

After 48-week treatment, the estimated mean changes in HbA1c in normal-weight, overweight, and obese patients were -1.9%, -1.8%, and -1.5%, respectively (P = 0.290 among groups after adjustment for baseline values). There were similar declines in FPG and 0.5- and 2-hour PPG among groups. There were non-significant trends from normal-weight to overweight to obese patients for increased weight reduction (decreases of 2.2, 3.9, and 4.0 kg, respectively; P = 0.104) and changes in waist circumference (decreases of 2.2, 3.2, and 5.6 cm, respectively; P = 0.078).

CONCLUSIONS

Baseline BMI had no effect on glycemic control, weight change, or other metabolic indices with exenatide monotherapy. Normal-weight patients with T2D would benefit from exenatide as much as overweight or obese patients on glucose control, without increased risk of excess weight loss.

Gain in adiposity over 3 years is associated with progressive renal decline in multi-ethnic South-east Asians with type 2 diabetes

BACKGROUND

This study evaluated the association between gain in adiposity and renal decline in a large prospective multiethnic South-east Asian cohort with type 2 diabetes mellitus (T2DM).

METHODS

Three years after the baseline visit, 2057 T2DM subjects were recalled for reassessment. The final cohort comprised 1014 subjects and was categorized into tertiles based on changes in body weight (ΔWt), body mass index (ΔBMI), visceral fat area (ΔVFA), and BMI-adjusted VFA (ΔVFA_BMI ). Outcomes included annual and rapid (≥3 mL/min per 1.73 m² per year) decline in estimated glomerular filtration rate (eGFR) and progression of albuminuria.

RESULTS

Participants (mean [±SD] age 57 ± 11 years, 48.8% women, BMI 27.7 ± 5.4 kg/m² ) exhibited a median annual decline in eGFR of 1.0 mL/min per 1.73 m² . Compared with the lower tertiles, Tertile 3 of ΔWt, ΔBMI, ΔVFA, and ΔVFA_BMI had the highest anthropometric increase, albeit of modest magnitude, and this was accompanied by the worst renal outcomes (all P < 0.05). The relationship between annual eGFR decline and Tertile 3 of ΔWt, ΔBMI, and ΔVFA_BMI persisted after multivariate adjustment in men but not in women. In addition, Tertile 3 of ΔWt, ΔBMI, ΔVFA, and ΔVFA_BMI predicted rapid eGFR decline. Anthropometric gains were also associated with progression of albuminuria.

CONCLUSIONS

Modest longitudinal gain in adiposity was associated with progressive renal decline in T2DM patients, suggesting that increased adiposity over time adversely affects renal outcomes. Therefore, a carefully designed weight-neutral or -loss antidiabetic treatment regimen is important when managing T2DM in the clinic.