This study shows that energy drink intake is associated with risky behaviours and suboptimal physical status, such as obesity, e-cigarette use, smoking, binge drinking, and use of illicit drugs, and highlights the complexity of the public health problems related to consumption of these products. Our results are also consistent with previously reported associations between energy drink intake and risky behaviours, especially among teenagers and young adults, including illicit drug use, alcohol dependence and binge drinking, prescription drug misuse, and other harmful outcomes^{(16,17,25,26,30)}. For example, Buja et al. (2017)⁽³¹⁾ found that caffeinated energy drink consumption was associated with negative impacts on digital well-being, revealed by problematic social network site usage among young teenagers in North-eastern Italy. An Icelandic study additionally showed that adolescent caffeine consumption was associated with self-reported physically aggressive behaviours towards others, including punching and kicking other individuals⁽³²⁾. Finally, researchers have also reported significant associations between increased energy drink consumption and suicide attempts among teenagers in South Korea and Ontario, Canada^(7,33). Overall, energy drink consumption has been correlated with risky behaviours that can have short-term, long-term, and/or permanent negative effects, especially among youth.

Much of the current literature on caffeinated energy drinks focuses on teenagers and younger/college-age adults^(17,18), as well as military personnel who may be of a similar age as many enlist or are conscripted as young adults^(19–21). Few studies, however, appear to assess the effects of caffeinated energy drinks among adults who are older than college age, and even fewer look together at risky behaviours among them and their offspring. Lieberman et al. analysed 2007–2012 NHANES data for adults aged 19+ years, primarily looking at demographic factors, as well as some health status characteristics and risky behaviours associated with all caffeine intake (not just caffeinated energy drink consumption); they found that smoking, higher calorie intake and alcohol consumption (when adjusted for employment factors) were associated with increased caffeine usage⁽³⁴⁾. In a study of energy drink intake among illicit drug users who participated in the online 2014 Global Drug Survey of individuals aged 16 years or older, Peacock et al. (2017)⁽²⁷⁾ found that over two-thirds of participants reported ever consuming energy drinks and higher levels of energy drink use were associated with several risky health behaviours, including use of tobacco, marijuana, amphetamine, 3,4-methylenedioxymethamphetamine (MDMA/ ecstasy) and cocaine.

Given the general dearth of energy drink consumption and risky behaviour data among adults, and the potential for adverse health outcomes from these behaviours, we believe that our study provides a unique opportunity to assess the behaviours that may accompany energy drink consumption among slightly older adults – study participants were generally older than those considered in much of the literature, with participant mean baseline ages ranging from a college student age common in the literature of 19·61 years (GUTS non-consumers) to a much older 33·96 years (NHS3 non-consumers). Furthermore, our study found several risky behaviours associated with energy drink consumption in a large, robust sample size. Additionally, we assessed certain risky behaviours related to energy drink use that have not often been assessed in the literature, including tanning bed use, lifetime number of sexual partners and use of muscle enhancement supplements. These findings help shed light on health issues and activities of concern to both the general public and, perhaps, also serve as a warning sign for medical and other health practitioners to look for other unsafe behaviours as well.

A potential limitation with our study is that the two cohorts are fundamentally very different in terms of their sample source. However, we believe that the benefits of pooling the cohorts outweigh this limitation. First, although population characteristics are different between the two cohorts, we found similar associations for many variables, showing the robustness of our findings. Second, the heterogeneity in associations for some variables allows us to have a better understanding of the associated patterns of energy drink intake. Third, by combining the NHS3 and GUTS, our study has ample power to achieve a strong conclusion of our research question, particularly in the presence of overall low energy drink consumption. Another limitation is that some of the data used for the GUTS analysis is from 2011, meaning that behaviours and other relevant information may have changed since the data were collected.

Limitations of addressing different study periods and exposure windows notwithstanding, as previously mentioned, an analysis of CAERS and NPDS data found that consumption of caffeinated energy drinks could lead to a variety of serious and life-threatening events, including tachycardia and other cardiac disorders, nervous system irregularities, nausea/vomiting and even death⁽³⁾. A recent systematic review of thirty-two studies found that insomnia was frequently associated with energy drink consumption, both among children and adults⁽³⁵⁾. Other studies have also reported associations between energy drink consumption and cardiac outcomes, including life-threatening arrhythmias^(10,11), and possibly hepatic and kidney damage⁽³⁶⁾. While most consumption of caffeine can be generally considered safe⁽³⁷⁾, use of caffeinated energy drinks can present health-threatening risks⁽³⁾ that warrant consideration in conjunction with the other unhealthy behaviours addressed in this analysis.

Certain limitations constrained this study, which nevertheless identified several characteristics and risky behaviours correlated with energy drink use in adults. First, even though the study used data from longitudinal cohort studies, the cross-sectional analysis restricted our ability to assess temporality between consumption of energy drinks and behaviours⁽¹⁷⁾; therefore, we are unable to determine if consumption of energy drinks actually led to the risky behaviours, if the risky behaviours simply happened concurrently with energy drink use, and/or if the behaviours actually preceded energy drink intake. Furthermore, we are unable to see if and/or how energy drink consumption may have changed over time and whether such variability would affect the associations detected in the cross-sectional analysis. When data from future iterations of questionnaires among the same cohorts become available, conducting longitudinal analysis will be possible, which in turn will help further elucidate these potential relationships and provide better insight to potentially inform consumer outreach and education and public health interventions going forward. Finally, we could not analyse the relationship between the specific products (e.g. individual brands) and the behaviours assessed, because user characteristics and health outcomes can vary by product⁽³⁾.