Publication Bias: The Elephant in the Review

Is chocolate consumption associated with health outcomes? An umbrella review of systematic reviews and meta-analyses

BACKGROUND & AIMS

The literature regarding the potential health benefits of chocolate consumption are unclear and the epidemiological credibility has not been systematically scrutinized, while the strength of the evidence is undetermined. We therefore aimed to map and grade the diverse health outcomes associated with chocolate consumption using an umbrella review of systematic reviews.

METHODS

Umbrella review of systematic reviews of observational and intervention studies (randomized placebo-controlled trials, RCTs). For each association, random-effects summary effect size, 95% confidence interval, and 95% prediction interval were estimated. We also assessed heterogeneity, evidence for small-study effect and evidence for excess significance bias. For significant outcomes of the RCTs, the GRADE assessment was furtherly used.

RESULTS

From 240 articles returned, 10 systematic reviews were included (8 of which included a meta-analysis), including a total of 84 studies (36 prospective observational studies and 48 interventional). Nineteen different outcomes were included. Among observational studies, including a total of 1,061,637 participants, the best available evidence suggests that chocolate consumption is associated with reduced risk of cardiovascular disease (CVD) death (n = 4 studies), acute myocardial infarction (n = 6), stroke (n = 5) and diabetes (n = 6), although this was based on a weak evidence of credibility. Across meta-analyses of intervention studies, chocolate consumption was positively associated with flow-mediated dilatation at 90-150 min (n = 3) and at 2-18 weeks (n = 3), and insulin resistance markers (n = 2). However, using the GRADE assessment, the evidence for these outcomes was low or very low. Data from two systematic reviews, reported that chocolate consumption was not associated with better depressive mood or cognitive function.

CONCLUSIONS

There is weak evidence to suggest that chocolate consumption may be associated with favorable health outcomes.

The Association between Lead and Attention-Deficit/Hyperactivity Disorder: A Systematic Review

The etiology of Attention-Deficit/Hyperactivity Disorder (ADHD) is complex and multifactorial. Although the development of ADHD symptoms remains to be elucidated, in recent years, epigenetic processes have emerged as candidate mechanisms. Lead is one of the most dangerous environmental pollutants, and it is suspected to be associated with ADHD. The aim of the present study was to review the epidemiological literature currently available on the relation between lead exposure and the diagnosis of ADHD. The PubMed and EMBASE databases were searched from 1 July 2018 up to 31 July 2018. The authors included observational studies (cohort, case⁻control and cross-sectional studies) published in English carried out on children within the last 5 years, measuring lead exposure and health outcomes related to ADHD. Seventeen studies met the inclusion criteria: 5 of these studies found no association between lead exposure and ADHD whereas the remaining 12 studies showed positive associations, even though not all of them were homogeneous in terms of exposure periods considered or ADHD diagnosis. To conclude, the evidence from the studies allowed us to establish that there is an association between lead and ADHD and that even low levels of lead raise the risk. However, there is still a lack of longitudinal studies about the relationship between lead exposure and the development of ADHD. Given the potential importance for public health, further research that includes the entire potential risk factors for ADHD in children must be encouraged.

Monoclonal gammopathy of undetermined significance and bone health outcomes: a systematic review and exploratory meta-analysis

Monoclonal gammopathy of undetermined significance (MGUS) is a common condition in the elderly. A number of studies have investigated the relationship between MGUS and bone health outcomes including bone mineral density (BMD), osteoporosis and fractures, but no meta-analysis exists. We conducted a systematic review and exploratory meta-analysis comparing bone health outcomes in patients with MGUS. Two independent authors searched PubMed and Scopus from inception until 19 October 2016. A meta-analysis of cross-sectional and longitudinal studies investigating fractures and BMD was conducted. Standardised mean differences (SMD) ± 95% confidence intervals (CIs) were calculated for BMD, and risk ratios (RRs) were calculated for prevalent and incident fractures. Of 174 initial hits, 10 studies of moderate methodological quality were eligible, including 8711 individuals with MGUS vs. 52,865 controls. Compared to controls, subjects with MGUS showed significantly lower values for radial cortical volumetric BMD (1 study; SMD = -5.45, 95% CI: -7.24 to -3.66), but not at the lumbar spine, femoral neck or hip. The incidence of fractures was higher in people with MGUS (n = 7466) vs. controls (n = 52,304) (RR = 1.36, 95% CI 1.28-1.44, I 2 = 0%) over a median of 12.5-year follow-up. The incidence of vertebral fractures was particularly elevated (RR = 2.50, 95% CI 1.53-4.06) although limited to two studies. In conclusion, although with limitations, our preliminary meta-analysis suggests that patients with MGUS are at higher risk of fractures despite evidence for differences in BMD being equivocal. Future longitudinal research is required to confirm our findings and determine if fracture prevention interventions are warranted in people with MGUS.