The triangular association of ADH1B genetic polymorphism, alcohol consumption and the risk of depression in older men

Association between dietary habits and the risk of migraine: a Mendelian randomization study

Objective

The important contribution of dietary triggers to migraine pathogenesis has been recognized. However, the potential causal roles of many dietary habits on the risk of migraine in the whole population are still under debate. The objective of this study was to determine the potential causal association between dietary habits and the risk of migraine (and its subtypes) development, as well as the possible mediator roles of migraine risk factors.

Methods

Based on summary statistics from large-scale genome-wide association studies, we conducted two-sample Mendelian randomization (MR) and bidirectional MR to investigate the potential causal associations between 83 dietary habits and migraine and its subtypes, and network MR was performed to explore the possible mediator roles of 8 migraine risk factors.

Results

After correcting for multiple testing, we found evidence for associations of genetically predicted coffee, cheese, oily fish, alcohol (red wine), raw vegetables, muesli, and wholemeal/wholegrain bread intake with decreased risk of migraine, those odds ratios ranged from 0.78 (95% CI: 0.63-0.95) for overall cheese intake to 0.61 (95% CI: 0.47-0.80) for drinks usually with meals among current drinkers (yes + it varies vs. no); while white bread, cornflakes/frosties, and poultry intake were positively associated with the risk of migraine. Additionally, genetic liability to white bread, wholemeal/wholegrain bread, muesli, alcohol (red wine), cheese, and oily fish intake were associated with a higher risk of insomnia and (or) major depression disorder (MDD), each of them may act as a mediator in the pathway from several dietary habits to migraine. Finally, we found evidence of a negative association between genetically predicted migraine and drinking types, and positive association between migraine and cups of tea per day.

Significance

Our study provides evidence about association between dietary habits and the risk of migraine and demonstrates that some associations are partly mediated through one or both insomnia and MDD. These results provide new insights for further nutritional interventions for migraine prevention.

The alcohol flushing response is associated with the risk of depression

The alcohol flushing response is experienced by 36–45% of East Asians after they consume a small amount of alcohol. Because individuals with this response are unable to metabolize the toxic acetaldehyde derived from alcohol effectively, the response offers a potential indicator of the health risks associated with alcohol intake. Depression is a major health problem linked to alcohol consumption; it might also be associated with the alcohol flushing response. Therefore, we examined the association between the alcohol flushing response and the risk of depression in the general population of South Korea. Our analysis included 139,380 participants and used data from the 2019 Korean Community Health Survey. Only current drinkers were considered in the analysis. The relationship between the alcohol flushing response and depression was evaluated by logistic regression analysis using SAS 9.4. Of the participants, more than one-third were current flushers; compared to never flushers, current flushers had a significantly greater risk of depression (adjusted odds ratio [AOR] 1.23, 95% confidence interval [CI] 1.12–1.34, P < 0.001). Former flushers did not exhibit a risk of depression. The risk of depression was significantly greater among alcohol flushers who drank < 15 g alcohol/day (< 5 g alcohol/day: AOR 1.20, 95% CI 1.07–1.35, P = 0.002; 5–14.9 g alcohol/day: AOR 1.39, 95% CI 1.13–1.70, P = 0.002). In conclusion, a large number of South Koreans experience the alcohol flushing response; compared with never flushers, current flushers are more likely to develop depression with a small dose of alcohol (< 15 g alcohol/day).

Frequent Cannabis Use Moderates the Relationship Between Sexual Dysfunction and Depression Among Female German Adults

BACKGROUND

Sexual dysfunction and heavy substance use (alcohol, tobacco, and cannabis) play an important role in the development of depression, while frequent substance use affects sexual dysfunction.

AIM

This study aimed to investigate the association between sexual dysfunction and depression among German adults in a nationally representative sample and the effect of alcohol, tobacco, and cannabis use on this association using moderator analysis.

METHODS

Data come from the German Health and Sexuality Survey (GeSiD) with N = 4,955 men and women aged between 18 and 75 years. We used multiple logistic regression analysis to examine the moderation effect of substance use between sexual dysfunction and depression by including an interaction term.

OUTCOMES

Self-reported diagnosed and treated depression within the last 12 months and the moderation effect of substance use on the association between sexual dysfunction and depression.

RESULTS

Men and women with at least 1 sexual dysfunction were more likely to be affected by depression as compared to those without sexual dysfunction. A moderation effect of frequent cannabis use was found between sexual dysfunction and depression among women.

CLINICAL IMPLICATIONS

Clinicians and therapists addressing addiction, depression, and dysfunction should keep the complex interactions in mind.

STRENGTHS & LIMITATIONS

This study provides new data on the association between sexual dysfunction and depression among German adults in a nationally representative sample and the moderation effect of substance use on this association. Further studies should disentangle the pathways between sexual dysfunction, cannabis use, and depression through moderated mediation analyses.

CONCLUSION

Frequent cannabis use plays a moderating role in the association between sexual dysfunction and depression among German adult women. Belau MH, Wiessner C, Becher H, et al. Frequent Cannabis use Moderates the Relationship between Sexual Dysfunction and Depression Among Female German Adults. J Sex Med 2022;19:940-949.

Effect of vortioxetine in subjects with major depressive and alcohol use disorders: a 6-month retrospective analysis

BACKGROUND

Major depressive disorder (MDD) and alcohol use disorder (AUD) are highly comorbid, with greater clinical complexity and psychosocial impairment. Several antidepressants have been used in this population, with mixed results. This preliminary study aims to investigate the effects of the multimodal antidepressant vortioxetine in MDD + AUD subjects.

METHODS

We retrospectively evaluated 57 MDD + AUD and 56 MDD outpatients, matched for baseline characteristics. Patients were assessed after 1, 3, and 6 months treatment with vortioxetine (10-20 mg/d, flexibly dosed) in combination with continuous psychosocial support. The primary outcome was improvement in depressive symptoms measured by the Montgomery-Åsberg Depression Rating Scale. We also investigated changes in anxiety, anhedonia, cognition, functioning, quality of life, and clinical global severity using the following instruments: Hamilton Anxiety Rating Scale, Snaith-Hamilton Pleasure Scale, Digit Symbol Substitution Test, Perceived Deficits Questionnaire-Depression, Functioning Assessment Short Test, Quality of Life Index, and Clinical Global Impression-Severity Scale.

RESULTS

Vortioxetine significantly improved mood in MDD + AUD patients (P < .001), with no differences when compared to MDD (P = .36). A substantial rate (45.6%) of comorbid subjects obtained clinical remission at endpoint (P = .36 vs MDD). We additionally observed baseline to endpoint improvements on all secondary outcomes (P < .001), with no significant difference between groups. Overall, vortioxetine was safe and well tolerated.

CONCLUSIONS

Given its effectiveness on mood, cognition, and functioning, its good safety and tolerability profile, and low potential for abuse, vortioxetine could represent a valid pharmacological intervention in MDD + AUD patients as part of an integrated therapeutic-rehabilitation program.

Using Mendelian randomization analysis to better understand the relationship between mental health and substance use: a systematic review

BACKGROUND

Poor mental health has consistently been associated with substance use (smoking, alcohol drinking, cannabis use, and consumption of caffeinated drinks). To properly inform public health policy it is crucial to understand the mechanisms underlying these associations, and most importantly, whether or not they are causal.

METHODS

In this pre-registered systematic review, we assessed the evidence for causal relationships between mental health and substance use from Mendelian randomization (MR) studies, following PRISMA. We rated the quality of included studies using a scoring system that incorporates important indices of quality, such as the quality of phenotype measurement, instrument strength, and use of sensitivity methods.

RESULTS

Sixty-three studies were included for qualitative synthesis. The final quality rating was '-' for 16 studies, '- +' for 37 studies, and '+'for 10 studies. There was robust evidence that higher educational attainment decreases smoking and that there is a bi-directional, increasing relationship between smoking and (symptoms of) mental disorders. Another robust finding was that higher educational attainment increases alcohol use frequency, but decreases binge-drinking and alcohol use problems, and that mental disorders causally lead to more alcohol drinking without evidence for the reverse.

CONCLUSIONS

The current MR literature increases our understanding of the relationship between mental health and substance use. Bi-directional causal relationships are indicated, especially for smoking, providing further incentive to strengthen public health efforts to decrease substance use. Future MR studies should make use of large(r) samples in combination with detailed phenotypes, a wide range of sensitivity methods, and triangulate with other research methods.

Risk factors and consequences of depression in later life: Findings from the health in men study (HIMS)

Background

The Health In Men Study (HIMS) has been collecting data on risk factors and health events for the past 25 years in a large community-representative sample of older men. This paper summarises key-findings of the study about depression in later life.

Methods

Narrative review of selected HIMS studies published over the past 15 years describing risk factors associated with prevalent and incident depression in older men, as well as clinical outcomes associated with depression.

Results

Data from HIMS showed that cardiovascular diseases and risk factors are associated with increased risk of depression, but this association is neither specific nor causative. Findings from HIMS are not supportive of the vascular hypothesis of depression in later life. Studies investigating lifestyle have generated risk tables capable of guiding risk reduction strategies. Other potentially modifiable risk factors associated with depression in the HIMS cohort included abnormal allostatic inflammatory response, high plasma homocysteine and low testosterone. The results from HIMS also showed that depression is most likely a prodromal manifestation of dementia rather that a true risk factor, but it increases frailty and mortality. The association between depression and suicide in older men is largely mediated by deteriorating health and increasing frailty.

Conclusion

HIMS has contributed to advance knowledge about risk factors associated with depression, as well as the health consequences of depression in older men. The study is ongoing and the investigators welcome the opportunity to share data with colleagues who are interested in the health of older people.

Prevalence of anxiety and depression symptoms, and association with epidemic-related factors during the epidemic period of COVID-19 among 123,768 workers in China: A large cross-sectional study

BACKGROUND

COVID-19 has gained intense attention globally. However, little is known about the COVID-19-ralated mental health status among workers.

METHODS

The cross-sectional online survey with 123,768 workers was conducted from February 2, 2020 to February 7, 2020 on a mega-size labor-intensive factory in Shenzhen, China. Oral consent was obtained prior to the questionnaire survey. The information collected in the survey included demographic characteristics, psychological symptoms, COVID-19-related information, and demands for psychological education and interventions. Symptoms of anxiety and depression were measured by the Zung's Self-Rating Anxiety Scale and Self-Rating Depression Scale. Logistic regression models were performed to determine the association between related factors and mental health status.

RESULTS

The prevalence of anxiety and depression symptoms was 3.4% and 22.8%, respectively. The dominant epidemic-related factors were having confirmed cases in the community (odds ratio [OR], 2.75, 95% CI, 2.37-3.19) and having confirmed friends (OR, 2.44; 95% CI, 1.69-3.52) for the increased risk of anxiety and depression symptoms, respectively. Nevertheless, major traditional risk factors such as general or poor health status and always drinking alcohol were still the dominant factors associated with the increased risk of anxiety and depression symptoms. Overall, 67.3% and 26.8% workers reported desire for psychological education and interventions, respectively.

LIMITATIONS

All assessments were self-reported, resulting in a risk of method bias.

CONCLUSIONS

Our findings show a relatively low prevalence of anxiety symptoms, a relatively high prevalence of depression symptoms, and urgent demand for psychological education and interventions among workers during the COVID-19 outbreak.

Alcohol Use and Depression: A Mendelian Randomization Study From China

Background: Alcohol use has been linked to a number of physical conditions, but the relationship between alcohol drinking and depression, one of the most common mental disorders that is a significant contributor to the global burden of disease, is still under debate. We aim to help fill the literature gap on the causal effect of alcohol use on depression by using genetic instruments of ALDH2 rs671 and ADH1B rs1229984 in the Mendelian randomization (MR) framework.

Materials and Methods: We collected a sample of 476 middle-aged and older adults from mainland China. The 10-item Center for Epidemiologic Studies Depression Scale (CESD-10) was used to measure the status of depression. The frequency and intensity of alcohol consumption were measured by (1) a binary indicator of drinking or not, (2) the total number of drinking occasions during the past 30 days, and (3) the weekly ethanol consumption in grams.

Results: MR estimates indicated that alcohol use was causally associated with a lower risk of depression. Parameter estimates of drinking or not (b = −0.127, p = 0.048), number of drinking occasions (b = −0.012, p = 0.040), and weekly ethanol consumption (b = −0.001, p = 0.039) were all negative and statistically significant. The results were robust after adjustments for potential confounders (e.g., income, smoking, and parental drinking behaviors), and the exclusion of heavy or former drinkers.

Conclusions: This is one of the first study to investigate the causal relationship between alcohol use and mental health using an MR design in East Asian populations. Further studies are needed to clarify the mechanisms of this causal link.

Effect of alcohol use disorders and alcohol intake on the risk of subsequent depressive symptoms: a systematic review and meta-analysis of cohort studies

BACKGROUND AND AIMS

Alcohol use disorders (AUD) are often comorbid with depressive symptoms. Cohort studies on the association between AUD and subsequent depressive symptoms have produced inconsistent results. Moreover, regarding alcohol intake, the risk of developing depressive symptoms might vary with alcohol intake level. We aimed to investigate the association between AUD, alcohol intake and subsequent depressive symptoms.

DESIGN AND SETTING

We conducted a systematic search in PubMed, Embase and PsycINFO for cohort studies on the association between AUD or alcohol intake and subsequent depressive symptoms.

PARTICIPANTS

We included 338 426 participants from 42 studies. Six and four studies analyzed only females and males, respectively.

MEASUREMENTS

We combined risk estimates for developing depressive symptoms using a random-effects model. We divided alcohol intake into abstinence, light (0-84 g/week), moderate (85-168 g/week) and heavy drinking (> 168 g/week or > 48 g/day at least weekly). We conducted a categorical analysis to compare the risk of depressive symptoms between abstinence and different intake categories. Further, we conducted a dose-response analysis to investigate the alcohol-depression association.

FINDINGS

We analyzed 42 studies (follow-up time: 1-40 years). AUD was associated with significantly increased risk of subsequent depressive symptoms [relative risk (RR) = 1.57, 95% confidence interval (CI) = 1.41-1.76]. Regarding alcohol intake, heavy drinking had an increased risk of depressive symptoms; however, the association was only significant when controls were limited to non-heavy drinkers (RR = 1.13, 95% CI = 1.05-1.22). Taking into consideration the possibility of publication bias and confounding factors made the association non-significant. We observed J-shaped associations in both categorical and dose-response analyses where light-moderate drinking had a significantly decreased risk of depression, while heavy drinking did not show a significant association with depressive symptoms compared with non-drinkers.

CONCLUSION

Alcohol use disorders are associated with increased the risk of subsequent depressive symptoms. Heavy drinking does not significantly predict occurrence of depressive symptoms after adjusting for potential confounders.

Recent advances in genetic studies of alcohol use disorders

PURPOSE OF REVIEW

Alcohol use disorder (AUD) is a complex genetic disorder with very high heritability. This polygenic disorder not only results in increased morbidity and mortality, it is also a substantial social and economic burden on families and the nation. For past three decades, several genetic studies were conducted to identify genes and pathways associated with AUD. This review aims to summarize past efforts and recent advances in genetic association studies of AUD and related traits.

RECENT FINDINGS

Initial genetic association studies achieved a limted success and suffered from low power due to small sample sizes. AUD is a polygenic trait and data from several thousands individuals was required to identify the genetic factors of small effect sizes. The scenario changed recently with technological advances and significant reduction in cost of the genome wide association analyses (GWAS). This enabled researchers to generate genomic data on mega biobanks and cohorts with access to extensive clinical and non-clinical phenotypes. Public access to data from biobanks and collaborative efforts of researchers lead to identification of several novel loci associated with AUDs and related traits. Efforts are now underway to identify the causal variants under the GWAS loci to identify target genes and biological mechanisms underpining AUDs. Many GWAS variants occur in promoter or enhancer regions of the genes and are involved in regulation of gene expression of causal genes. This, large amounts of "omics" data from projects such as "ENCODE", RoadMap and GTEx is also helping researchers to integrate "multi-omics" data to interpret functional significance of GWAS variants.

SUMMARY

With current review, we aim to present the recent advances in genetic and molecular studies of AUDs. Recent successes in genetic studies of AUDs will definetely motivate researchers and lead to better therapeutic interventions for this complex disorder.

Evidence of causal effect of major depression on alcohol dependence: findings from the psychiatric genomics consortium

BACKGROUND

Despite established clinical associations among major depression (MD), alcohol dependence (AD), and alcohol consumption (AC), the nature of the causal relationship between them is not completely understood. We leveraged genome-wide data from the Psychiatric Genomics Consortium (PGC) and UK Biobank to test for the presence of shared genetic mechanisms and causal relationships among MD, AD, and AC.

METHODS

Linkage disequilibrium score regression and Mendelian randomization (MR) were performed using genome-wide data from the PGC (MD: 135 458 cases and 344 901 controls; AD: 10 206 cases and 28 480 controls) and UK Biobank (AC-frequency: 438 308 individuals; AC-quantity: 307 098 individuals).

RESULTS

Positive genetic correlation was observed between MD and AD (rgMD-AD = + 0.47, P = 6.6 × 10-10). AC-quantity showed positive genetic correlation with both AD (rgAD-AC quantity = + 0.75, P = 1.8 × 10-14) and MD (rgMD-AC quantity = + 0.14, P = 2.9 × 10-7), while there was negative correlation of AC-frequency with MD (rgMD-AC frequency = -0.17, P = 1.5 × 10-10) and a non-significant result with AD. MR analyses confirmed the presence of pleiotropy among these four traits. However, the MD-AD results reflect a mediated-pleiotropy mechanism (i.e. causal relationship) with an effect of MD on AD (beta = 0.28, P = 1.29 × 10-6). There was no evidence for reverse causation.

CONCLUSION

This study supports a causal role for genetic liability of MD on AD based on genetic datasets including thousands of individuals. Understanding mechanisms underlying MD-AD comorbidity addresses important public health concerns and has the potential to facilitate prevention and intervention efforts.

Alcohol consequences, not quantity, predict major depression onset among first-year female college students

Alcohol use and its consequences have often been associated with depression, particularly among female college students. Interpretation of this association has been challenging due to potential reverse causation. The current study sought to clarify the temporality of these relationships. We examined: (1) the association between alcohol consumption and onset depression among female college students, and (2) the association between drinking consequences and onset depression among drinkers only. We used a prospective longitudinal design. Participants were first-year female college students who completed a baseline survey at study entry, and monthly assessments of alcohol consumption, drinking consequences, and depression symptoms. Cox proportional hazards regression with time-varying covariates were constructed among the full sample (N = 412) and the drinkers only sample (N = 335). Adjusted hazard ratios accounted for known risk factors for depression such as race/ethnicity, academic challenge, not getting along with one's roommate, sexual victimization prior to college, marijuana use, and socioeconomic status. For each additional average drink per week, adjusting for all covariates, there was no (95% CI: -4%, +4%) increased risk of onset depression. For each additional alcohol consequence, adjusting for all covariates, there was a 19% (95% CI: 5%, 34%) increased risk of onset depression. This significant relationship remained after adjusting for quantity of alcohol consumption. Quantity of alcohol consumed did not predict incident depression. However, experiencing alcohol consequences, regardless of consumption, did increase the risk of incident depression. College substance use and mental health interventions should aim to reduce not only alcohol consumption, but also alcohol-related consequences.

Different patterns of alcohol consumption and the incidence and persistence of depressive and anxiety symptoms among older adults in Ireland: A prospective community-based study

BACKGROUND

The associations of different patterns of alcohol consumption and the incidence and persistence of depressive and anxiety symptoms in older age remain unclear.

METHODS

Data on 6095 adults aged ≥ 50 years old from the Irish Longitudinal Study on Aging (TILDA) was analyzed. Participants completed the CAGE instrument to screen for problematic alcohol use at baseline between October 2009 and February 2011. Outcomes were incident (assessed by the CES-D scale) and anxiety (assessed by the Hospital Anxiety and Depressive scale) symptoms after a two-year follow-up as well as persistence of probable depression and anxiety among those with a positive screen for those disorders at baseline. Associations were adjusted for potential confounders through multivariable models.

RESULTS

In the overall sample, problem drinking did not predict incident and persistent depression and anxiety in this sample. Among females, problem drinking increased the risk for incident depression (OR = 2.11; 95%CI = 1.12-4.00) and anxiety (OR = 2.22; 95%CI = 1.01-4.86). In addition, problem drinking increased the risk of persistent depressive symptoms (OR = 2.43; 95%CI = 1.05-5.06) among females.

CONCLUSION

Problem drinking may increase the risk of incident probable depression and anxiety among older females. Furthermore, problem drinking led to a higher likelihood of persistent depressive symptoms in older female participants. Interventions targeting problem drinking among older females may prevent the onset and persistence of depression in this population, while also decreasing the incidence of anxiety symptoms.

Mapping risk factors for depression across the lifespan: An umbrella review of evidence from meta-analyses and Mendelian randomization studies

The development of depression may involve a complex interplay of environmental and genetic risk factors. PubMed and PsycInfo databases were searched from inception through August 3, 2017, to identify meta-analyses and Mendelian randomization (MR) studies of environmental risk factors associated with depression. For each eligible meta-analysis, we estimated the summary effect size and its 95% confidence interval (CI) by random-effects modeling, the 95% prediction interval, heterogeneity with I², and evidence of small-study effects and excess significance bias. Seventy meta-analytic reviews met the eligibility criteria and provided 134 meta-analyses for associations from 1283 primary studies. While 109 associations were nominally significant (P < 0.05), only 8 met the criteria for convincing evidence and, when limited to prospective studies, convincing evidence was found in 6 (widowhood, physical abuse during childhood, obesity, having 4-5 metabolic risk factors, sexual dysfunction, job strain). In studies in which depression was assessed through a structured diagnostic interview, only associations with widowhood, job strain, and being a Gulf War veteran were supported by convincing evidence. Additionally, 8 MR studies were included and provided no consistent evidence for the causal effects of obesity, smoking, and alcohol consumption. The proportion of variance explained by genetic risk factors was extremely small (0.1-0.4%), which limited the evidence provided by the MR studies. Our findings suggest that despite the large number of putative risk factors investigated in the literature, few associations were supported by robust evidence. The current findings may have clinical and research implications for the early identification of individuals at risk for depression.

ADH1B: From alcoholism, natural selection, and cancer to the human phenome

The ADH1B (Alcohol Dehydrogenase 1B (class I), Beta Polypeptide) gene and its best-known functional alleles, Arg48His (rs1229984, ADH1B*2) and Arg370Cys (rs2066702, ADH1B*3), have been investigated in relation to many phenotypic traits; most frequently including alcohol metabolism and alcohol drinking behaviors, but also human evolution, liver function, cancer, and, recently, the comprehensive human phenome. To understand ADH1B functions and consequences, we provide here a bioinformatic analysis of its gene regulation and molecular functions, literature review of studies focused on this gene, and a discussion regarding future research perspectives. Certain ADH1B alleles have large effects on alcohol metabolism, and this relationship particularly encourages further investigations in relation to alcoholism and alcohol-associated cancer to understand better the mechanisms by which alcohol metabolism contributes to alcohol abuse and carcinogenesis. We also observed that ADH1B has complex mechanisms that regulate its expression across multiple human tissues, and these may be involved in cardiac and metabolic traits. Evolutionary data strongly suggest that the selection signatures at the ADH1B locus are primarily related to effects other than those on alcohol metabolism. This is also supported by the involvement of ADH1B in multiple molecular pathways and by the findings of our recent phenome-wide association study. Accordingly, future studies should also investigate other functions of ADH1B potentially relevant for the human phenome. © 2017 Wiley Periodicals, Inc.

Excessive alcohol consumption increases mortality in later life: a genetic analysis of the health in men cohort study

We designed this cohort study of men aged 70-89 years to determine if excessive alcohol use increases mortality. They reported history of alcohol use (never, past, ≤ two daily drinks, two to four daily drinks, four to six daily drinks, > six daily drinks) and donated a blood sample in 2001-2004. We determined the ADH1B rs1229984 G>A polymorphism and retrieved mortality data from the Western Australian Data Linkage System. Other study measures included age, education, body mass index, smoking, and history of hypertension, diabetes, chronic respiratory diseases, coronary heart disease and stroke. Of the 3496 participants, 225 (6.4 percent) carried the ADH1B rs1229984 G>A polymorphism. Carriers consumed significantly less alcohol than non-carriers. The adjusted mortality hazard ratio (MHR, 95 percent confidence interval-95%CI) over 8.0 years (range: 10 weeks to 11.2 years) relative to never drinkers was 1.15 (95%CI = 0.86, 1.55) for past drinkers, 0.98 (95%CI = 0.76, 1.25) for men consuming ≤ two daily drinks, 1.13 (95%CI = 0.85, 1.49) for two to four drinks, 1.18 (95%CI = 0.81, 1.71) for four to six drinks and 1.87 (95%CI = 1.11, 3.12) for those consuming more than six daily drinks on a regular basis. The MHR associated with the ADH1B rs1229984 G>A polymorphism was 0.68 (95%CI = 0.54, 0.87). Excessive alcohol use in later life is associated with increased mortality, and this association is likely to be causal. We found no evidence that light to moderate alcohol use decreases the mortality of older men. Health messages regarding the safe use of alcohol in older age may benefit from taking these findings into account.

Mendelian randomization studies: a review of the approaches used and the quality of reporting

BACKGROUND

Mendelian randomization (MR) studies investigate the effect of genetic variation in levels of an exposure on an outcome, thereby using genetic variation as an instrumental variable (IV). We provide a meta-epidemiological overview of the methodological approaches used in MR studies, and evaluate the discussion of MR assumptions and reporting of statistical methods.

METHODS

We searched PubMed, Medline, Embase and Web of Science for MR studies up to December 2013. We assessed (i) the MR approach used; (ii) whether the plausibility of MR assumptions was discussed; and (iii) whether the statistical methods used were reported adequately.

RESULTS

Of 99 studies using data from one study population, 32 used genetic information as a proxy for the exposure without further estimation, 44 performed a formal IV analysis, 7 compared the observed with the expected genotype-outcome association, and 1 used both the latter two approaches. The 80 studies using data from multiple study populations used many different approaches to combine the data; 52 of these studies used some form of IV analysis; 44% of studies discussed the plausibility of all three MR assumptions in their study. Statistical methods used for IV analysis were insufficiently described in 14% of studies.

CONCLUSIONS

Most MR studies either use the genotype as a proxy for exposure without further estimation or perform an IV analysis. The discussion of underlying assumptions and reporting of statistical methods for IV analysis are frequently insufficient. Studies using data from multiple study populations are further complicated by the combination of data or estimates. We provide a checklist for the reporting of MR studies.