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Table 7 Summary of findings of the effect of different levels of alcohol consumption compared to no or very low level (zero to <10 g/week) consumption on cognition

From: Long-term effects of alcohol consumption on cognitive function: a systematic review and dose-response analysis of evidence published between 2007 and 2018

Certainty assessmentImpactCertaintyImportance (of outcome)
№ of studiesStudy designRisk of biasInconsistencyIndirectnessImprecisionOther considerations
Cognition (women only) (follow up: range 3 years to 13 years; assessed with: various scales and tests (standardised mean difference))
 5observational studiesvery serious aserious bnot seriousnot serious cnoneThere was no important difference in cognitive function between women who consumed one to two standard drinks (<20 grams of alcohol) per day and non-drinkers but the evidence is very uncertain.
For alcohol consumption less than 25.9 grams alcohol/day (the point at which the predicted lower bound of the confidence interval crosses zero; ~2.5 standard drinks), cognition was slightly better in those consuming alcohol than current non-drinkers. However, the SMDs were small, with a maximum SMD of 0.18 (95%CI 0.02, 0.34), occurring at an intake of 14.4 grams alcohol/day. The effects are particularly uncertain at higher levels of alcohol consumption (>30 grams per day), since only one study (Kesse-Guyot 2012) contributes data for these levels of intake.

VERY LOW
CRITICAL
Cognition (men only) (follow up: range 1 years to 13 years; assessed with: various scales and tests (standardised mean difference))
 6observational studiesvery serious aserious dnot seriousnot serious cnoneThere was no important difference in cognitive function between men who consumed one to two standard drinks (<20 grams of alcohol) per day and non-drinkers but the evidence is very uncertain.
The maximum SMD of 0.05 (95%CI 0.00, 0.10), occurring at an intake of 19.4 grams alcohol/day, was very small. For all levels of alcohol consumption, the predicted lower bound of the confidence interval of the SMD indicated that cognition was similar or poorer as compared to current non-drinkers, but the SMDs were small for alcohol intakes less than 55 grams/day. The effects are particularly uncertain at higher levels of alcohol consumption (>30 grams per day), since only one study (Kesse-Guyot 2012) contributes data for these levels of intake.

VERY LOW
CRITICAL
Cognition (women and men) (follow up: range 3 years to 34 years; assessed with: various scales and tests (standardised mean difference))
 4observational studiesvery serious aserious enot seriousnot serious cnoneThere was no important difference in cognitive function between adults who consumed one to two standard drinks (<20 grams of alcohol) per day and non-drinkers but the evidence is very uncertain.
The maximum SMD of 0.24 (95%CI -0.03, 0.51) occurred at an intake of 25 grams alcohol/day. For higher levels of alcohol consumption (e.g. >55 grams alcohol/day) there may be detrimental effects on cognition, however, this is where there is most uncertainty in the predictions, since only one study (Kitamura 2017) contributes data for these levels of intake.

VERY LOW
CRITICAL
Cognition (young people up to age 25) (follow up: range 12 months to years; assessed by: any scale or test or diagnostic criteria)
 0      None of the included studies examined the effects of different levels of alcohol consumption on cognition among young people, or the effects of different levels of alcohol consumption up to age 25 on cognition over the life-course (any age). Note, studies examining only acute effects (intoxication or withdrawal) were ineligible for the review.-CRITICAL
  1. Explanations: a. Downgrade for very serious risk of bias. All studies were at serious risk of selection bias (due to lag time between initiating drinking and first alcohol measurement) and serious risk of misclassification of alcohol consumption status (no lifetime measures or measures of variation in consumption over time; recall bias). Also moderate-serious concern about bias arising from residual confounding and missing outcome data. b. Downgraded for serious inconsistency. There was evidence of heterogeneity in the study-specific dose-response coefficients (I2 = 69.5%, Q-test for heterogeneity p-value = 0.001). There are important differences between studies that may account for the observed heterogeneity, but it was not possible to explore whether these differences explained the observed heterogeneity. c. Not downgraded for imprecision despite wide confidence interval, since interpretation of the upper and lower bound of the interval suggests small, probably unimportant effects with considerable uncertainty due to the risk of bias and inconsistency. d. Downgraded for serious inconsistency. There was evidence of heterogeneity in the study-specific dose-response coefficients (I2 = 56.6%, Q-test for heterogeneity p-value = 0.011). There are important differences between studies that may account for the observed heterogeneity, but it was not possible to explore whether these differences explained the observed heterogeneity. e. Downgraded for serious inconsistency. There was evidence of heterogeneity in the study-specific dose-response coefficients (I2 = 47.2%). Differences between studies may account for the observed heterogeneity, but it was not possible to explore whether these differences explained the observed heterogeneity.