New research published in the journal Alcohol and Alcoholism suggests that moderate to heavy drinking tends to be associated with increased bodily inflammation, even for individuals who maintain a highly nutritious diet. The study provides evidence that eating well might not be enough to counter the harmful physical effects of frequent alcohol consumption.
Scientists Kailyn Lowder and Jimikaye Beck Courtney wanted to better understand how two common lifestyle factors, diet and alcohol consumption, interact to influence systemic chronic inflammation. Jimikaye Beck Courtney is an assistant professor and an A. Donald and Billie J. Stallings fellow at the University of North Carolina at Chapel Hill.
“I studied nutritional sciences during my undergraduate degree and began researching alcohol use during my postdoctoral fellowship,” Courtney said. “Across those experiences, I’ve been interested in the complexity of how both nutrition and alcohol use impact health outcomes.”
“For instance, past research indicated that moderate alcohol use may be protective against cardiovascular disease, but the U.S. Surgeon General more recently advised that any alcohol use increases cancer risk.”
Systemic chronic inflammation is a persistent, low level immune response. When the immune system is constantly activated in this way, it can induce oxidative stress and eventually damage healthy tissues. This persistent damage provides a foundation for various severe health conditions like cardiovascular disease, cancer, diabetes, and nonalcoholic fatty liver disease.
“The first author, Kailyn Lowder, was a master’s student in EXSS at UNC Chapel Hill who also had a nutrition background and was studying inflammation in cancer,” Courtney noted. “We were interested in investigating whether alcohol use was detrimental to inflammation after accounting for the healthfulness of a person’s diet.”
To answer these scientific questions, the researchers recruited 91 adults between the ages of 21 and 44 years old. The participants all had a Body Mass Index of 25 or higher, classifying them as either overweight or obese. Body Mass Index is a standard measurement tool that uses a person’s height and weight to estimate their total body fat.
The selected sample was predominantly White, non-Hispanic, and female. The study utilized an intensive longitudinal design, meaning the researchers tracked the participants closely over a relatively short period of 21 consecutive days.
At the beginning of the study, the participants filled out initial surveys detailing their typical drinking habits over the previous month. Based on this retrospective information, the researchers categorized the participants into four distinct groups. These categories included nondrinkers who consumed zero drinks, light drinkers who consumed up to three drinks per week, moderate drinkers who consumed up to 14 drinks per week for men or seven for women, and heavy drinkers who exceeded those moderate limits.
During the 21 days, participants answered daily smartphone surveys each morning to report their exact alcohol consumption. The participants also completed highly detailed dietary recall interviews at the start of the study and again at the end.
The researchers used this food data to calculate a total Healthy Eating Index score for each person. Higher scores indicate a healthier diet rich in whole grains, fruits, and vegetables, and lower in saturated fats.
At the end of the 21 days, the participants returned to the laboratory for a follow up blood draw. The researchers analyzed the blood samples for specific inflammatory markers known as cytokines. Cytokines are proteins that the immune system releases in response to stress or injury.
In small amounts, cytokines are a normal part of the body’s defense system. However, when they are persistently elevated, known as chronic low grade inflammation, they can contribute to the development of heart disease, cancer, and diabetes.
The specific cytokines measured included C-reactive protein, tumor necrosis factor alpha, interleukin 6, and interleukin 1 beta. C-reactive protein is one of the most commonly used clinical markers of inflammation because it can be measured with a routine blood test. Elevated levels of C-reactive protein have been associated with an increased risk of cardiovascular disease, diabetes, and other chronic conditions.
When looking strictly at the daily drinking logs from the 21 day period, the researchers found no significant associations between the daily average of drinks consumed and the levels of inflammatory proteins in the blood. However, when the scientists looked at the habitual drinking categories based on the past month of overall behavior, habitual alcohol consumption appeared to be detrimentally associated with specific inflammatory markers. This specific relationship remained intact even after factoring in how well the participants ate.
The scientists found significant differences based on biological sex regarding C-reactive protein levels. Females who fell into the moderate and heavy drinking categories had significantly higher levels of C-reactive protein compared to females who were only light drinkers. Interestingly, there were no such differences among the male participants in the study.
“I was somewhat surprised that males did not show any differences in inflammation (specifically C-reactive protein [CRP]) regardless of how much alcohol they consumed, whereas females had increased inflammation even when drinking moderately (4-7 drinks/week),” Courtney said. “This was surprising given previous research suggesting that moderate alcohol use may lower risk. In general, the results varied by inflammatory biomarker, showing how complicated the relationship is between nutrition, alcohol use, and inflammation.”
The authors note that females generally produce fewer of the enzymes needed to metabolize alcohol in the stomach and liver, and they tend to have less fat free body mass than males. These inherent biological differences mean females usually experience higher blood alcohol concentrations from the exact same amount of alcohol, which might explain their heightened inflammatory response.
When looking at tumor necrosis factor alpha, the scientists found that heavy drinkers of both biological sexes had significantly higher levels of this inflammatory protein compared to light drinkers. The researchers found no major associations between drinker type and interleukin 1 beta. For interleukin 6, female sex moderated the association among moderate drinkers, but the differences between the specific drinking groups were not statistically significant enough to draw firm conclusions.
Regarding overall diet, the researchers found that higher Healthy Eating Index scores were associated with slightly lower levels of C-reactive protein, tumor necrosis factor alpha, and interleukin 1 beta. Consuming more whole grains was linked to lower interleukin 6, while consuming more saturated fat was linked to higher interleukin 6. While eating a high quality diet did provide a small protective effect against inflammation, it did not cancel out the much larger spikes in inflammation seen in the moderate and heavy drinking categories.
“Inflammation increases disease risk, and alcohol use may exacerbate inflammation regardless of how healthy the rest of your diet is,” Courtney told PsyPost. “It’s worth noting that our study focused specifically on adults who were overweight or obese, so these findings may not apply equally to everyone, if you’re unsure what this means for you personally, it’s worth talking to your doctor. That said, if you are an adult who is overweight or heavier based on a body mass index > 25 kg/m², our findings suggest it may be worth avoiding more than 3 alcoholic drinks per week.”
Courtney also outlined a few limitations and potential misunderstandings regarding the findings. “It is important for readers to note that, although light drinking females (1-3 drinks/week) had lower CRP than moderate and heavy drinking females, they were not lower than non-drinkers,” Courtney said. “In other words, please do not interpret these findings to suggest that light drinking is better than non-drinking when it comes to inflammation.”
The researchers note that the findings might not apply to the broader general population or to people with different body compositions. “As well, this was a sample of disease-free adults who were overweight or heavier based on body mass index,” Courtney noted. “It’s possible that the impact of alcohol use and nutrition on inflammation could be different among adults who are normal weight, because overweight and obesity increase inflammation, as well as among adults who already have diseases like hypertension or diabetes.”
Additionally, the dietary data only covered two single days over the entire three week study period. Nutritionists generally recommend collecting dietary data over at least three or four days to get a truly accurate picture of a person’s habitual eating patterns. Another potential misinterpretation could arise from the reliance on self reported data for alcohol consumption.
“My overarching goal in research is to help people live healthier and happier lives by, for instance, helping them make informed decisions about whether drinking alcohol is a good decision for their health and well-being,” Courtney said. “For next steps, I’m continuing to investigate the impact of alcohol use and other lifestyle behaviors, like nutrition and physical activity, on inflammation to help achieve that long-term goal.”
Future research should aim to include larger and more diverse groups of people over extended periods of time. The scientists suggest that future studies could use objective measures of biological alcohol exposure, such as wearable alcohol sensors or breathalyzers, to eliminate the potential inaccuracies of self reporting.
“As with all research, replication and further investigation are always needed,” Courtney said. “In the meantime, guidance from medical organizations and the U.S. Surgeon General on alcohol use remains the best resource for making informed decisions about drinking. On that note, I want to highlight that Kailyn Lowder, the first author, was instrumental in this research, she is the one who initiated this specific research question. She’s an MD/PhD student, and I feel certain she is an upcoming leader in medicine and research.”
The study, “Moderate-to-heavy habitual alcohol use appears to be detrimentally associated with inflammation even when accounting for diet quality in humans: findings from an observational intensive longitudinal study,” was authored by Kailyn Lowder and Jimikaye Beck Courtney.
