Table of Contents
In the last 4 lessons I discussed the 3 primary macronutrients (protein, carbohydrate, and fat) as well as fiber, all of which are the building blocks of foods we eat. In this lesson I will discuss alcohol, the last macronutrient, and its impact on the dieting process as well as overall health.
Note: The impact of alcohol on health is controversial, and I discuss this in a lot of detail below to try to present a fair overview of the literature. For those who do not wish to read through all of this, you can get all the main points of this lesson by reading the:
- summary in the section of the short-term impact of alcohol on dieting and exercise
- 2020-2025 Dietary Guidelines for the Americas recommendation regarding alcohol intake listed at the beginning of the section of the long-term impact of alcohol on health
- summary in the section of the long-term impact of alcohol on dieting and health
- conclusion at the end
Short-term impact of alcohol on dieting and exercise
Considerations for short-term intake are much different than long-term intake. Short-term refers to within a single session. Binge drinking has negative impacts on health and I will not discuss this further as there is no controversy in the literature regarding this point. I will consider intermittent episodes of non-binge drinking here.
Impact on caloric consumption
A 2019 systematic review and meta-analysis (“SR/MA”) on the impact of alcohol consumption on food energy intake concluded that people generally do not compensate fully for the calories they consume through alcohol, meaning alcohol intake leads to greater energy intake overall.(Kwok, 2019) However, there were inconsistencies in some of the studies. The authors allude to the fact that other than heavy alcohol drinking (above the guideline listed below) there is no consistent association of alcohol intake with overweight and obesity, and wine has actually shown a protective effect against weight gain.
A 2021 narrative review came to similar conclusions.(Fong, 2021) The authors note that while alcohol intake can lead to greater caloric consumption acutely this does not seem to influence long term weight gain, potentially due to various compensatory mechanisms such as increased physical activity.
Note: Alcohol has 7 kcal per gram, but many alcoholic drinks also have added sugar that further increase their caloric content. All of this counts if you are counting calories. Alcohol does have a relatively high thermic effect of feeding (more similar to that of protein than to carbohydrate or fat), but as most people consume relatively low amounts of alcohol this will not have a meaningful impact on dieting overall. Click here for a calculator to determine the caloric intake of different alcoholic beverages.
A 2016 study attempted to examine the impact of decreasing alcohol intake in an overall weight management behavioral intervention.(Kase, 2016) Among other things, generic advice was given to decrease alcohol consumption. Over a 1-year time span a decrease in alcohol consumption was not associated with weight changes overall. However, when looking at subjects who were determined to have a high level of behavioral impulsivity, alcohol reduction was associated with weight loss. It is possible that these individuals benefit most from alcohol reduction as this may decrease disinhibition (leading to less caloric consumption). It is also possible that decreased alcohol intake led to a decrease in the general expectancy that they will eat more calories when consuming alcohol, thus leading to fewer calories being consumed on occasions of alcohol intake.
Impact on exercise
A 2018 review discussed the various studies showing how alcohol potentially disrupts muscle protein synthesis in a variety of different ways.(Kimball, 2018) The majority of the literature on this subject is based on in vitro and animal model studies; there is a paucity of human literature. As discussed in a separate review of the muscle protein synthesis response to meals after resistance training, one study in humans has shown a significant detrimental impact of binge drinking, but there is a lack of studies assessing the impact of only 1-2 drinks on muscle protein synthesis.(Trommelen, 2019)
Summary of the short-term literature
Thus, overall, there is no strong evidence in the literature that a low level of alcohol intake (consistent with the guideline listed below) will have a harmful effect on dieting and resistance training progress. This is also seen in longer term observational studies, with no association between alcohol intake and overweight/obesity in cohort studies and only a mild association (due to heavy alcohol consumption beyond the guideline discussed below) seen in cross-sectional studies.(Golzarand, 2021)
However, for individuals who are more prone to eating larger amounts of food with alcohol intake or who are more prone to take the mentality after consuming alcohol that they have “ruined” their dieting for the day and thus should do whatever they want and get back on track tomorrow, minimizing alcohol consumption would likely be helpful when actively dieting to lose weight.
Long-term impact of alcohol on health
The following note shows one set of guidelines for alcohol intake.
Note: Regarding alcohol intake, the 2020-2025 Dietary Guidelines for Americans recommends:
- 1 alcoholic drink-equivalent should be defined as containing 14 grams of pure alcohol (0.6 fluid ounces)
- This is equivalent to 12 fluid ounces of regular beer (5% alcohol), 5 fluid ounces of wine (12% alcohol), or 1.5 fluid ounces of 80 proof distilled spirits (40% alcohol).
- Females should consume no more than 1 drink daily and should especially avoid binge drinking (no more than 3 drinks in ~2 hours).
- Males should consume no more than 2 drinks daily and should especially avoid binge drinking (no more than 4 drinks in ~2 hours).
- People who do not currently drink alcohol should not begin drinking alcohol. Additionally, people should not drink alcohol if they are pregnant (or may be pregnant), younger than 21 years old*, recovering from alcoholism or unable to control the amount they drink, have certain medical conditions, or take certain medications that interact with alcohol.
The majority of the literature agrees with not going above these guidelines. However, there is significant controversy regarding whether alcohol intake within these guidelines provides a net health benefit or harm relative to abstaining from alcohol completely. There was even controversy when writing the 2020-2025 Dietary Guidelines for Americans regarding this specific point (see discussion here). I will attempt now to present a fair overview of this debate.
Several review articles have been published over the years discussing potential benefits and harms of alcohol. A 2012 review discussed some of these findings but concluded there was inconsistency in the literature and that it was too soon to recommend moderate consumption of ethanol as a strategy to promote better health.(Nova, 2012) A 2013 consensus document overviewing the beneficial and harmful aspects of alcohol intake that was then updated in 2015 stated many of the same findings.(Poli, 2013; Poli, 2015) The authors concluded that abstainers should not be advised to start drinking but that people keeping intake within the guideline listed above should not be encouraged to decrease their intake. Also in 2015 a separate review discussed cardiovascular risks and benefits of moderate & heavy alcohol consumption, noting there is publication bias with studies discussing outcomes and there is no definite benefit for all-cause mortality (“ACM”).(Fernández-Solà, 2015)
In 2016 a consensus document specifically focusing on beer came to many of these same findings as the prior reviews.(de Gaetano, 2016) These authors also stated that unless there is concern for a high risk of alcohol-related cancer there is no reason to encourage healthy adults with regular light-to-moderate volume beer intake to decrease their consumption, but they additionally added that there is no evidence that adult abstainers who start drinking alcoholic beverages in moderation reduce their risk of chronic disease.
Note: See below for a brief discussion of comparisons of different sources of alcoholic beverages (ie, beer vs wine).
A 2018 review article discussed several prior studies and reviews indicating a benefit of low level alcohol intake on cardiovascular mortality and other health parameters.(O’Keefe, 2018) The authors noted that benefits are seen more frequently in middle-aged and older individuals than younger-aged, there are ethnic differences, and many benefits last <24 hours (which may help justify regular low level intake for sustained benefit rather than intermittent intake). They also stated that studies show it is difficult to predict who will be at risk for problem drinking once they begin and they cite the American Heart Association’s recommendation that nondrinkers should not be advised to start drinking.
A separate 2018 review came to similar conclusions.(Goel, 2018) The authors here also noted that benefits are more often seen as one’s age increases and the risks of developing drinking problems and binge drinking may outweigh the benefits for the younger population. They also found ethnic differences. They concluded that 1-2 drinks daily is not dangerous but abstainers should not be encouraged to start drinking as there is no way to predict if a person would only consume alcohol in moderation after starting.
A 2019 review took a favorable view of low-level alcohol intake towards overall health, calling into question the methodology of the Stockwell and the Mendelian randomization analyses discussed below, suggesting both may be invalid.(Costanzo, 2019) Of note, this review was funded by the European Foundation for Alcohol Research and the International Scientific Forum on Alcohol Research.
Note: This is one of several topics in the field of nutrition where industry seems to exert some level of influence on research findings. While research sponsored by industry is not necessarily biased or untrustworthy, it is generally worth considering if the majority of the industry-sponsored research leans one way while non-industry-sponsored research takes a different point of view. See below for a more concrete example of the alcohol industry influencing research.
In 2019 another large review article on the impact of moderate alcohol consumption on cardiovascular disease (“CVD”) was published, echoing several of the findings discussed in the prior reviews.(Chiva-Blanch, 2019) The authors noted that women absorb alcohol differently due to lower body water, smaller stature, and lower gastric alcohol dehydrogenase content and that many studies have found sex-specific differences. Benefits for all-cause mortality (ACM) are typically only seen in white & Hispanic populations, not black/Indian/Chinese, and Asians seem to have a higher risk of hypertension & stroke at the same level of intake. Harmful effects of abusive or heavy intake, however, are the same throughout the globe. Findings from this review include:
- Moderate alcohol consumption seems to attenuate inflammation, decrease fibrinogen & fibrin D-dimer, increase tissue plasminogen activator & plasminogen concentrations, inhibit platelet reactivity, and increase HDL cholesterol.
- The risk of hypertension increases linearly with alcohol intake though <1-2 drinks daily with meals may not be detrimental.
- Low-to-moderate alcohol intake is associated with a decreased risk of heart failure and in people with CVD a lower incidence of ACM.
However, the authors mentioned that some data indicating benefits for ACM are only seen in generally older populations. They noted consumers who consider alcohol intake as healthy for CVD have been shown to consume 1.5x more alcohol than those who do not consider it healthy. They concluded stating it would be wise to suggest low-to-moderate alcohol consumption among current drinkers and to never recommend drinking in order to improve health.
A 2021 narrative review regarding the impact of alcohol on cardiovascular health highlighted much of the controversy, noting there is evidence of a negative impact of mild-to-moderate alcohol intake on some medical conditions as shown in their table reproduced below.(Stătescu, 2021)
The authors also highlighted differences in:
- race (light-to-moderate drinking is connected to lower risk of ACM in white individuals but not black individuals)
- ethnic origin (Italians experience improved health outcomes with low-to-moderate drinking while Chinese and Indians do not)
- genetic background
- type of alcoholic beverage (red wine may have greater health-promoting properties).
The authors acknowledged we need large randomized controlled trials. They recommended for individuals at high risk of CVD to minimize consumption and when consuming alcohol to consume wine at low-to-moderate intake.
A separate 2021 review of alcohol and cardiovascular health found some potential benefit at very low levels of intake (up to 1 drink daily) but also concluded there is a risk of harm for several conditions, there are many confounding factors in the literature, and an improvement in the overall body of evidence is needed to draw confident conclusions.(Roerecke, 2021)
In addition to all of the overview articles listed above, I will point out a handful of the more influential studies and then additional analyses that have been done in recent years.
Mendelian randomization analyses
In 2014 an important Mendelian randomization analysis was conducted.(Holmes, 2014) For a review of Mendelian randomization studies, particularly as it pertains to this analysis, please read through the following note prior to continuing. This can be a somewhat complicated concept and it is certainly not necessary to read through this note to understand the main point of this analysis discussed below.
Note: Mendelian randomization studies (some people prefer the term “genetic instrumental variable analysis”) essentially function as long-term randomized controlled trials. The idea is that a genetic variant is linked to a variable (ie, alcohol intake) which is then linked to an outcome (ie, coronary heart disease). For this analysis the authors looked at genetic mutations of ADH1B, which are known to be associated with decreased alcohol consumption. Thus, people with this mutation are “randomized” into a group that consumes less alcohol. Ideally this would be the only difference and thus if this group had different health outcomes it would be due to drinking less alcohol.
However, in practice there are other considerations, and this has led to some criticism of Mendelian randomization studies regarding alcohol intake. Some of these include:
- As this mutation alters the metabolism of acetaldehyde (a byproduct of alcohol breakdown in the body), if acetaldehyde directly influences any health benefits/harms then it will be unclear if health changes are due to different amounts of alcohol intake vs. different profiles of acetaldehyde metabolism.
- If this mutation associates with any other factors there can be confounding. As one example, this could occur if people who drink less alcohol are less likely to live a “party lifestyle” and are more likely to associate with other similar-minded individuals. Thus, there would be social differences between genetic carriers and non-carriers of the mutation and this could impact health outcomes.
- Any decrease in alcohol consumption due to this mutation would possibly extend to parental alcohol consumption prior to conception and possibly during pregnancy, which may substantially influence one’s health.
- If this mutation causes less alcohol consumption and moderate alcohol consumption is actually beneficial then this mutation may be associated with harm. However, if this mutation causes less binge drinking and binge drinking is detrimental then this mutation may be associated with benefit. Given potential competing factors, it can be hard to draw any definitive conclusion about what influences the actual health outcomes.
If curious, a 2020 publication addresses many of the criticisms that apply to the utilization of Mendelian randomization studies in general and in particular regarding alcohol intake.(Davey Smith, 2020)
This analysis was based on individual participant data from >260,000 people across 56 studies. The authors found that carriers of the variant allele consumed 17.2% less units of alcohol weekly, had an odds ratio of 0.70 of being in the top 1/3 of drinkers, had an odds ratio of 0.78 for binge drinking, and had an odds ratio of 1.27 of being abstainers from consuming alcohol. Thus, carriage of the variant allele was associated with all types of self-reported drinking behavior, which is important as this could then be used for analysis in individuals drinking amounts along the spectrum of low, moderate, and high alcohol quantities. The idea is that in any predefined bin of alcohol intake carriers would be drinking a lower amount of alcohol in that bin relative to non-carriers.
Their main finding was that for people who consumed alcohol, carriers had decreased odds (0.86) of coronary heart disease (“CHD”) compared to non-carriers. The same protective effect was seen at intakes of 0-6 units weekly, 7-20 units weekly, and ≥21 units weekly. Thus, as carriers consumed less alcohol in all of these different groups of alcohol intake, the fact that they had lower risk of CHD implies that alcohol increased the risk of developing CHD. Importantly, the risk was not decreased in abstainers, which implies the genetic variant itself did not provide protection from CHD.
In 2021 a SR of Mendelian randomization studies was published, including 24 such studies.(van de Luitgaarden, 2021) The authors noted a lot of heterogeneity in the methodology. Only one of these studies evaluated ACM, finding a detrimental effect of alcohol. However, 67% of the studies evaluating CVD and 75% of the studies evaluating diabetes found null effects. Thus, Mendelian randomization analyses provide variable results regarding the association of alcohol consumption with different health outcomes.
Concerns of abstainer bias
In 2016 a very large and influential SR/MA was published.(Stockwell, 2016) To understand the importance of this study, first please read the note below regarding abstainer bias.
Note: Most prospective studies on alcohol intake and its impact on mortality have historically considered people who abstain from alcohol intake to be a control group. They have then compared low, moderate, and heavy alcohol intake to the abstainers (different studies have defined low, moderate, and heavy in different ways).
The potential issue here is that many people who are former drinkers have quit in part due to health problems related to their prior drinking. When they enroll in one of these studies they may still be placed in the control group as they are currently abstaining from alcohol intake. This will lead to the abstainer group having worse outcomes and thus people drinking a low level of alcohol may appear to have better health outcomes in comparison. To try to eliminate this “abstainer bias”, it is important to separate “lifelong abstainers” from “former drinkers”. One caveat is that lifelong abstainers may have other confounding factors (ie, be part of certain religions or communities that abstain from alcohol) that could then influence health outcomes in other ways.
The authors specifically looked at 87 prospective studies that considered the relationship between alcohol intake and ACM. They noted that historically studies showed a low level of drinking yielded better outcomes than not drinking at all. When looking at all 87 studies they found a protective effect of occasional and low volume alcohol drinking for ACM (relative risk of 0.84 and 0.86, respectively). However, when only looking at the 13 studies free of abstainer bias, they found no benefit to occasional or low volume drinking. When looking at the 7 of these 13 studies considered to be higher quality, they still found no benefit of drinking alcohol at any level. Former drinkers had a 38% increased risk of mortality relative to lifetime abstainers. They noted that if occasional drinkers were used as the reference group, then the low volume group still would not have decreased risk, implying no level of alcohol intake leads to decreased risk of ACM.
Note: A commentary on this study brought up concerns that most of the studies only assessed alcohol intake once while drinking patterns change over time and that in a US national survey >50% of people describe themselves as lifetime abstainers in follow-up after reporting drinking previously.(Rehm, 2016) The vast majority of large epidemiologic studies in the nutrition field only measure exposure level one time at baseline, and this is a common (and valid) criticism as many people will have exposure levels vary over time. This is discussed further below. The concern of people misremembering or simply lying about prior exposure is also a common occurrence in the nutrition field (ie, as mentioned in Lesson 2 many people misreport the number of calories they consume). While these two criticisms are valid, I do not believe either invalidates the findings of this study.
Perhaps a more appropriate criticism would be the concern of confounding lifestyle variables for lifetime abstainers These lifestyle factors would be very difficult to control for and may considerably influence the outcomes regarding ACM.
After this analysis more attention has been paid to the control group utilized in studies. In 2017 an analysis of US data using the National Health Interview Survey (NHIS) from 1997-2009 linked with the National Death Index divided groups into lifetime abstainers, lifetime infrequent drinkers, former drinkers, current light drinkers, current moderate drinkers, and current heavy drinkers, and found benefits for death from ACM, cancer, heart disease, and cerebrovascular disease for the light and moderate drinkers (hazard ratios ~0.80 relative to lifetime abstainers).(Xi, 2017) These benefits were only seen in individuals who reported no binge drinking (one exception: for ACM people who took part in binge drinking <1 day monthly also saw benefit). More beneficial effects were seen as age increased. Of note, alcohol intake was only assessed one time in each participant.
A 2018 article looking at this same NHIS data (and also data from the VA (Veterans Affairs)) found the lowest risk of death when drinking ~3 times weekly in the NHIS data and 2-3 times weekly in the VA data, with increased risk when drinking ≥5 days weekly.(Hartz, 2018) Of note, both of these data sets had alcohol measured only once and used in-person surveys (previously shown to yield underreporting of alcohol intake relative to anonymous surveys).
Additionally in 2018, a large analysis using data from 2016 looking at alcohol use globally across a large variety of health outcomes concluded that the optimal level of intake when looking at all health conditions is 0 drinks daily, though the authors found similar results with 1 drink daily.(GBD, 2018) The only health conditions for which they found a benefit of alcohol intake were ischemic heart disease and diabetes mellitus. For the majority of health outcomes they looked at they found increased risk of harm at any level of alcohol intake.
Another large study came out in 2018 that looked at almost 600,000 current drinkers across 83 studies.(Wood, 2018a) Here the authors excluded abstainers due in part to the various concerns noted above. Thus, they were attempting to determine for people who drink alcohol what level of intake is associated with the best outcomes. Of interest, ~71,000 of these participants from 37 studies had repeat measures of alcohol consumption and they calculated a regression dilution ratio of 0.50 (see note below for an explanation; similar to above this is a somewhat complicated concept and also is not necessary to understand the main points of the analysis).
Note: Regression dilution bias comes from the concept that there will always be some variability in measurements. This can come from instrument error (ie, lack of precision in the measuring device), but for the consideration of alcohol intake the big concern here (as well as other areas of nutrition) is that people may vary their intake over time. Hence, if measurements are done at baseline but not throughout the study then categorizing people by their baseline level of intake may not reflect their intake throughout the study. As health outcomes will more generally reflect past alcohol intake at all time points and not just the baseline time point of a given study, this will weaken (“dilute”) the calculated association (calculations are frequently done via some method of regression) between the health outcome and alcohol intake. Hence the phrase “regression dilution bias”.
By using repeat measurements over time, you can estimate the strength of this regression dilution, and then this can be applied as a correction factor.(Clarke, 1999) So, given a regression dilution ratio of 0.50, this implies that the regression coefficient relating health outcomes to baseline alcohol intake is ~1/2 the corrected regression coefficient relating health outcomes to alcohol intake throughout the study duration. Thus, the associations may be twice as strong as what studies that only consider baseline measurements indicate.
The authors found the lowest risk of ACM as well as CHD (not including myocardial infarction) with alcohol intake <100 grams weekly. The mean intake for the <100g intake group was 56 grams weekly (4 standard drinks). They found blood pressure and HDL cholesterol (the “good” cholesterol) increased with increasing alcohol consumption. For any given volume of weekly alcohol intake, they saw worse outcomes in people who drank less frequently (thus implying more potential binging). One commentary on this study noted that there were not worse numbers when drinking up to 200g weekly (14 standard drinks) in individuals who spread this out to ≥3 days weekly.(Thompson, 2018) The original authors caution in a response that <50% of the recorded deaths had drinking frequency information and there were wide confidence intervals when attempting to examine the hazard ratio for the association of binge drinking & disease outcomes, implying they do not have a complete enough data set to conclusively support that observation.(Wood, 2018b)
A 2019 publication used data from the Health and Retirement Study that examined elderly individuals over 15 years, separated lifetime abstainers from former drinkers, took measures of alcohol intake every 2 years (one of the few studies with repeat measurements), and considered many confounders.(Keyes, 2019) They found that occasional and low levels of alcohol intake had a hazard ratio of 0.81-0.93 for ACM relative to abstention. However, they also did not find an increased risk for heavy drinkers, which is not what has typically been seen previously; they attribute this to possible errors with self-reporting or reverse causation where people who are unhealthy decrease their alcohol intake. It is unclear to what degree this calls into question the overall results of the study.
A 2021 analysis of UK Biobank data (this is a cohort of individuals aged 40-69 years at baseline with lots of health metrics tracked and followed over many years) found that for multiple different organ evaluations by MRI, increased alcohol intake at any level of intake was associated with likely pathologic changes (ie, decreased brain volume, increased left ventricular mass, decreased descending aorta distensibility, and increased liver fat).(Evangelou, 2021) On average these changes were relatively small; it’s unclear if certain individuals may be more susceptible to greater pathologic changes.
A separate 2021 analysis of UK Biobank data found that among people who consume alcohol regularly(Jani, 2021):
- Predominantly spirits and beer/cider drinkers had higher health risks (including ACM, major adverse cardiovascular events, liver cirrhosis, and accidents/self-harm) than predominantly red wine drinkers.
- Splitting alcohol consumption over 3-4 days led to better health outcomes than 1-2 days (regarding ACM and major adverse cardiovascular events) or daily consumption (regarding liver cirrhosis).
- Consuming alcohol with meals led to better health outcomes than consuming alcohol in isolation.
Of interest, this study also considered a small subset of the cohort (n=15,750) who had repeat measurements of alcohol consumption. Of these individuals:
- 90% reported a change in the amount of weekly alcohol units they consumed (on average there was a decease by 1.5 drinks over time)
- 48.6% had a change in the predominant type of alcohol they consumed
- 46.3% had a change in at least 1 aspect of their alcohol consumption pattern from baseline
- 40.5% had a change in frequency of consumption
- 31.8% had a change in their alcohol consumption pattern with respect to meals
When repeating the above analyses with this subset of individuals and considering their changes in alcohol consumption over time there was no consistent effect of alcohol type or consumption pattern with outcomes, though the confidence intervals were very large implying there were too few subjects to determine meaningful differences.
Thus, this data set further shows the potential peril of only including baseline alcohol intake measurements.
A 2021 analysis of dose-response relationships for alcohol use and various diseases using lifetime abstention as the reference group noted that most diseases have monotonic increasing relationships (meaning the risk continually increases as alcohol intake increases).(Rehm, 2021) The two exceptions seem to be ischemic diseases (such as heart attacks and stroke) and diabetes. For prevention of these diseases an intake of 10-20 grams daily may be optimal though the protective effect is greater in females than males.
Additional analyses of prospective cohorts have been done as well:
- Two cohort studies examined ethnic groups previously shown to have higher health risks with alcohol intake:
- A 2021 prospective cohort study of Chinese individuals found the lowest composite risk of mortality, CVD, and cancer with 1-25 grams of alcohol intake weekly (≤2 standard alcoholic drinks per week).(Zhang, 2021)
- A 2021 prospective cohort study of Korean adults found a dose-response relationship where increasing alcohol intake at any level associated with increased cancer mortality.(Ko, 2021)
- A 2021 analysis of 16 cohorts (15 European, 1 Australian) found that alcohol intake of ~5 grams daily (which is ~3 drinks weekly) was associated with a reduced risk of ACM, cardiovascular mortality and other causes of mortality other than mortality from cancer (no association was seen with cancer mortality at this level of intake).(Di Castelnuovo, 2021)
Lastly, a 2022 Mendelian randomization analysis using the UK Biobank data found that any level of alcohol intake increases the risk of hypertension and coronary artery disease.(Biddinger, 2022) The risk is only minimally increased when consuming up to 7 drinks weekly but increases considerably from that point upward, as shown in the figure below. Of interest, in this cohort individuals with light-to-moderate drinking levels have healthier lifestyle habits than those who abstain from alcohol, which would mask the harmful effect of alcohol consumption when comparing light-to-moderate consumers to those who abstain.
Alcohol and cancer
In 2014 a MA was published that attempted to synthesize all of the available evidence to determine a dose-response relationship of alcohol intake with site-specific cancer incidence.(Bagnardi, 2015) The authors presented data for the relative risk of light, moderate, and heavy alcohol intake, which they describes as consuming on average ≤12.5, >12.5 but ≤50, and >50 grams of alcohol per day, respectively. I have reproduced their figure for this data below.
They also presented dose-response curves for the site-specific cancer types; I have reproduced their figure for this data below.
A group of authors in 2021 published updated estimates of the global burden of cancer attributable to alcohol consumption.(Rumgay, 2021b) In this analysis the authors considered global alcohol consumption patterns in 2010 and subsequent cancer incidence in 2020, under the assumption there will be a ~10 year lag time between alcohol intake and cancer development. They also used relative risk numbers from the World Cancer Research Fund (“WCRF”) Continuous Update Project:
- Click here for the WCRF page on alcohol, if you download the available document you can find the specific relative risk numbers per 10 grams of alcohol intake on page 25.
- If curious, the reason I included the separate data above (despite the WCRF report being more recent) is because the report only provided the relative risks in a 10 gram per day increment, which is less informative than separating the risk based on light, moderate, and heavy intake if the risk is non-linear.
The authors combined the alcohol intake estimates with the cancer incidence and relative risk data to determine what percentage of the cancer cases could be attributed to alcohol consumption. They specifically focused on the cancer types with more confirmatory data regarding a causal impact of alcohol intake. I have reproduced their data below showing the number of cases of each type of cancer attributed to alcohol consumption as well as the population attributable fraction for each type of cancer below:
- Esophageal – 189,700 cases; population attributable fraction = 31.6%
- This means 189,700 cases were due to alcohol intake and almost 1/3 of cases of esophageal cancer were due to alcohol intake.
- Liver – 154,700; 17.3%
- Breast – 98,300; 4.4%
- Colon – 91,500; 8.1%
- Lip and oral cavity – 78,900; 20.2%
- Rectal – 65,100; 9.0%
- Pharyngeal – 39,400; 22%
- Laryngeal – 27,600; 15%
- Total – 741,300; 4.1%
Note: The above data does indicate alcohol consumption of any level will increase the risk of some types of cancers. However, as all of the data was observational, it is important to keep in mind that correlation does not necessarily mean causation. For example:
- Perhaps confounding factors that were not perfectly accounted for, such as smoking associated with alcohol intake, explain some of the increased risk of cancer.
- Several Mendelian randomization studies have not found associations between alcohol intake and cancer incidence, at least for some sites such as breast cancer.(Rumgay, 2021b) As discussed above Mendelian randomization studies are not perfect but this also indicates confounding factors may play a role.
- Perhaps people under-reported their level of alcohol consumption; this would make low levels of alcohol intake seem more harmful than it actually is.
- The abstainer bias mentioned above could be a factor here as well; this would make alcohol intake seem less harmful than it actually is.
Even though it is difficult to know exactly how much of an increased risk alcohol consumption contributes to cancer incidence, as alcohol is known to exert direct carcinogenic effects it is unlikely that there is no impact of alcohol consumption on cancer incidence given the above data. If this is a concern for you then you can consider decreasing your alcohol consumption accordingly.
Summary of the long-term evidence
Overall, it is very difficult to determine the true impact of low levels of alcohol intake relative to abstaining from alcohol consumption. The various reviews highlight potential improvements in biomarkers with low levels of alcohol intake, but it’s not clear how this translates to health outcomes in the long run. The Mendelian randomization analyses generally show increased health risks with alcohol consumption but have significant potential confounding aspects as alluded to above. While the above cohort studies and other analyses generally indicate more optimal health outcomes with low levels of intake at or below the lower level of the dietary guidelines (ie, 3 drinks spread throughout the week), it seems any level of alcohol consumption may increase the risk of cancer, and there are many important variables to consider:
- the total quantity of alcohol consumed
- alcoholic beverage choice
- the pattern of alcohol consumption
- whether alcohol is or is not consumed with meals
- changes in the above four variables over time
- the reference group considered and any confounding factors this may generate
- current non-drinkers may include people who have stopped drinking due to poor health
- lifetime abstainers may have other differing lifestyle factors that influence health outcomes
- genetic risk differences between different study groups
Given all of these variables and the conflicting results, it is not possible to state conclusively one way or another from the literature described above if a low level of alcohol intake yields superior health benefits to no intake at all, let alone if any such guidance would apply to all individuals equally. As summarized in a fairly recent overview of this controversy, large randomized trials would be the next step to try to determine the true health impact of low levels of alcohol consumption.
Large randomized trial?
It is clear that some studies find benefits of alcohol consumption and some do not. Ideally, we could conduct a randomized trial over an extended period of time to determine what health outcomes are observed. Recently there was going to be a randomized trial (“Moderate Alcohol and Cardiovascular Health” trial) to help answer some of these questions. This was going to attempt to enroll 7,800 people, randomize them into groups of low-level intake or no intake of alcohol, and compare incidence of new cases of CVD as well as new cases of diabetes. However, it required and garnered so much financial support from the alcohol industry that the industry was beginning to influence the study significantly. Due to this, an NIH investigation was conducted and the study was shut down due to the likely bias.(Mitchell, 2020)
I have not come across any literature to suggest further randomized controlled trials are currently being planned. Without these trials it will be very difficult, if not impossible, to resolve the controversy alluded to above.
Sources of alcohol
Overall, much of the research looks at alcohol intake as a whole and does not break sources down to wine, beer, spirits, etc. A 2021 SR evaluating prospective cohort analyses found no consistent differences in health outcomes between wine, beer, and spirits when examining their association with ACM, CVD, diabetes, and various cancers.(Estruch, 2021) However, the authors acknowledge there can be many confounding factors that mask any significant associations. This was emphasized in a separate 2021 review, finding predominantly wine drinks had healthier overall lifestyles than predominantly beer drinkers, who themselves had healthier overall lifestyles than predominantly spirit drinkers.(Kosti, 2021)
That said, there is some evidence that fermented alcoholic beverages (ie, beer and wine) may provide better health effects than distilled beverages (ie, liquors and spirits) due to fermentation yielding a higher concentration of bioactive compounds (ie, polyphenols).(Chiva-Blanch, 2019) These are typically most present in red wine > white wine > beer, while they are at much lower concentrations in liquors and spirits. Of note, specifically regarding polyphenols, strong evidence regarding a beneficial impact of their consumption is lacking (their consumption is thought to be beneficial but this has not been shown conclusively).(Visioli, 2020)
Nonetheless, beer itself has still been shown to have several potential health benefits at low levels of intake.(de Gaetano, 2016; Spaggiari, 2020; Marcos, 2021) Given many confounding factors between lifestyles of people who prefer wine vs beer vs liquor it is difficult to draw firm conclusions; as indicated above some prospective cohort analyses indicate beer consumption is harmful regarding mortality risk.(Jani, 2021) For individuals who do choose to consume alcohol, until further evidence suggests otherwise, wine, particularly red wine, may be the alcoholic beverage of choice from a health perspective.
So what can I ultimately conclude regarding alcohol intake and its impact on health? I think the jury is still out regarding if there is a net benefit with low level of intake over an extended period of time. It is possible that any true cardiovascular benefit would be “cancelled out” by an increased risk of harm from cancer. The epidemiologic research base has many controversial components as discussed above (due to issues with self-reporting of intake, many confounding factors, and a general lack of repeat measurements over time) No randomized controlled trials have been performed in part due to influence from the alcohol industry.
With the documented risk that initiating alcohol consumption may lead to progressively heavier consumption, and no overwhelming evidence of a net benefit at low intake levels, I agree with the authors of most of the reviews and the dietary guidelines listed above that alcohol intake should be kept at a low volume of intake for people who do consume alcohol (and should preferentially consume red wine, white wine, or beer, likely in that order of preference), binging should be avoided, and people who abstain should not be encouraged to begin consuming alcohol. For people who are dieting, if alcohol consumption triggers greater caloric intake then this should be minimized if possible.
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