This study involving a very large stratified random sample of military SMs found that 45 % of SMs used ≥ 1 SRNS at least once per week and use of sport drinks, bars, and gels was reported by 32, 27, and 3 % of SMs, respectively. Multivariable logistic regression indicated that greater use of any SRNS was independently associated with male gender, younger age, single marital status, more weekly aerobic or resistance training, tobacco use, higher alcohol intake, officer status, combat arms occupations, and service in the Marine Corps or Navy (compared to the Air Force). Overall, the proportion of users reporting ≥ 1 AE was 2.0 %, with 1.3 % for sport drinks, 1.6 % for sport bars, and 2.8 % for sport gels.
Prevalence
The use prevalence of sport drinks was previously reported in several military and civilian studies. Among Australian soldiers, 42 % reported consuming sport drinks ≥ 1 time/wk [18], and among British soldiers 49 %, reported using sport drinks “currently” [19]. Among young adults in the US (18 to 31 year of age), 31 % reported consuming sport drinks ≥ 1 time/week [20], and in a representative sample of the entire US population (18 to > 65 year of age), 15 % reported sport drink consumption “on a regular and consistent basis” [11]. Previous US military studies [4,5,6] found sport drinks were used by 24, 23, 51, and 36 % of Air Force, Army, Marine Corps, and Navy personnel, respectively. In these same four services, the current study found use prevalence of 29, 34, 43 and 30 %, respectively. Overall, these data indicate that the prevalence of sport drink use among US SMs is lower than among Australian and British soldiers, similar to young adults in the US, and higher than in the general US population. In making comparisons among prior US military studies [4,5,6] it should be noted that the Army, Air Force, and Navy/Marine Corps data was collected in 2006–2007, 2010–2011, and 2011–2012, respectively. Thus, these data also suggest that sport drink use may have increased over time in the Air Force and Army while it has decreased in the Marine Corps and Navy.
The prevalence of sport bar and gel use have also been reported previously in several studies. Among Australian soldiers, 6 and 3 % reported use of either sport bars or gels ≥ 1 time/week, respectively [18], and among British soldiers “current” use of these supplements was reported by 18 and 10 %, respectively [19]. About 11 % of the general US population reported use of sport bars on a “regular and consistent basis” in 2011 [11]. Previous studies of US military personnel [4,5,6] conducted between 2006 and 2012 have combined sport bar and sport gel use and report that 9, 6, 22 and 23 % of Air Force, Army, Marine Corps and Navy personnel, respectively, use these supplements. This compares to 25, 27, 35, and 28 % of these four services in the current study. Overall, these data suggest that sport bar and sport gel use is considerably higher among US soldiers compared to Australian soldiers and the general US population. British soldiers have a lower use of sport bars than US soldiers but higher use of sport gels. Considering the temporal factors mentioned above (i.e., how long ago studies were conducted), these data also suggest use of these supplements has increased over time in all services, especially the Air Force and Army.
A meta-analysis [3] of 18 studies encompassing a wide range of athletic samples found that 44 % (95 %CI = 24–66 %) of male athletes and 35 % (95 %CI = 22–51 %) of female athletes used sport drinks; however, as indicated by the 95 %CIs, there was a very wide range of prevalence depending on the sport and country of origin. The current study found that 34 and 23 % of male and female SMs, respectively, used sport drinks. Summary prevalence estimates from 10 studies reporting on athletes’ use of sport bars found that 28 % (95 %CI = 14–56 %) of male athletes and 32 % (95 %CI = 22–51 %) of female athletes used this supplement [3], compared to 28 and 21 % of men and women in the present study. Thus, compared to a wide range of athletic populations, SM use of sport drinks is, on average, lower. Prevalence of sport bar use among male athletes and male SMs is similar, but female athletes tend to use sport bars more often than female SMs.
Factors associated with SRNS use
In agreement with the current study, most [5, 6, 11, 12, 18, 21, 22], but not all [4, 11, 22] investigations have been relatively uniform in demonstrating that the proportion of individuals who used sport drinks decreased with age; was higher among men; those who were single; those employed in combat arms occupations; and had little association with BMI. No previous investigation has reported these factors in multivariable analysis, but in the current investigation, these relationships were generally maintained in the logistic regression when all variables were considered together. On the other hand, previous studies [4,5,6, 11, 12] have not been consistent in finding associations between sport gel/bar use and these factors. In the current study, the relationship between sport bar/gel use was similar to that of sport drinks in that use was highest among younger age groups and was higher among men and those in combat arms occupations. However, in contrast with sport drinks, married SMs and those with BMI in the 25.0-29.9 kg/m2 range had the highest use of sport bars/gels. Marine Corps personnel had the highest use of all three SRNS types in both univariate and multivariable analyses.
Previous studies [4,5,6, 18, 21, 22] have been generally consistent in reporting that sport drink and sport bar/gel use increases as physical activity increases, in agreement with the current study. Military personnel are much more physically active compared to civilian populations [23, 24] because they must acquire and maintain a relatively high level of physical fitness to pass regular physical fitness tests [25] and because of heavy physical requirements in many occupational specialties [26]. The fact that use of all types of SRNSs was higher as the duration of training increased is likely because SRNSs are often used in connection with sport and exercise activity and as individuals train more, they are more likely to use SRNSs. Interestingly, in the current study sport gel use was substantially higher with higher levels of aerobic or resistance training in the univariate analysis. However, in multivariable analysis the relationship between sport gel use and resistance training duration was severely attenuated while that with aerobic exercise was considerably enhanced. This suggested that aerobic exercise duration had a much stronger relationship with sport gel use compared to resistance training duration.
In the current study, tobacco users (current smoker or smokeless tobacco user) were more likely to use SRNSs, and as alcohol consumption increased there was increased use of all three types of SRNSs. In multivariable analysis, the relationship between smoking and sport bar and sport gel use was no longer significant, but the other relationships were maintained. A number of studies that have examined smoking and SRNSs have shown little association between smoking and sport drink or sport bar/gel use [4, 12, 20], but two investigations [21, 22] found adolescent smokers were about twice as likely as nonsmokers to use sport drinks. The reasons for the conflicting results are not apparent. In univariate and multivariable analyses in the current study, alcohol use demonstrated a strong and dose-related relationship with sport drinks, bars, and gels in that use of these SRNSs was higher with increasing levels of alcohol consumption. No previous studies could be found on this relationship, suggesting further research is required.
Adverse effects
In the present study, the prevalence of self-reported AEs for all types of SRNSs was low with 1.3, 1.6, and 2.8 % of SMs reporting ≥ 1 AE for sport drinks, bars, and gels, respectively. In a previous study of Navy and Marine Corps personnel, 3.7 % of participants reported ≥ 1 AE for sport drinks and 3.1 % for sports bars/gels [6]. The AE prevalence for SRNSs is in contrast to dietary supplements for which 8–29 % of military SMs have previously reported AEs, but largely using convenience samples [6, 13, 27,28,29,30,31,32,33]. Data recently collected on a large stratified random sample of SMs reported that 18 % of DS users reported AEs, near the middle of this range [13]. Nutritional supplements like SRNSs are regulated by the FDA as foods and are subject to the regulatory framework of the Federal Food, Drug, and Cosmetic Act of 1938, and the numerous modifications to that act since 1938 [34, 35]. This legislation prescribes that no substance can be introduced into the US food supply unless it has been “generally recognized as safe” meaning that “there is a reasonable certainty in the mind of competent scientists that the substance is not harmful under its intended conditions of use” [36]. By statute, a “Nutrition Fact” label is required on the food packaging, and that label must contain all ingredients by their common name and in descending order of amount [36]. In contrast, DSs are controlled under the DSHEA of 1994 [8], which gives the FDA limited regulatory authority. Manufacturers must notify the FDA before marketing a new DS, but FDA approval is not required for retailing the product. The FDA has the burden of demonstrating a specific product is unsafe, although manufacturers are required to notify the FDA about serious AEs [37, 38]. A “Supplement Facts” label is required on DS packaging that must show the ingredients in the supplement [39], but for proprietary blends, amounts of the ingredients are not required. The low incidence of AEs among SRNSs examined here suggest regulation as “foods” results in a lower incidence of AEs compared with DSs which are regulated separately.
Strengths and limitations
The current study had the advantage of employing a very large random sample of SMs that was stratified on known demographics of gender and military service. The questionnaire was standardized and based on previous questionnaires designed for obtaining similar supplement data from SMs [16]. Nonetheless there were some limitations to this study. All data were self-reported and suffer the usual weaknesses associated with this method including recall bias, social desirability, errors in self-observation, and inadequate recall [40, 41]. An attempt was made to mitigate some of these factors by requesting SRNS use only in the last 6 months. In self-reporting AEs, participants were limited to nine AE categories, although they could report and describe other AEs that were subsequently categorized by the investigators. Matching SRNS use with AEs reported in clinical medical records would have provided a more definitive description of the AEs.
