Introduction and research questions
Nowadays, citizens in industrialized countries can look forward to a high life expectancy. The crucial element for being able to enjoy this long life is good health. Public-policy makers aim to improve citizens’ health to ensure quality of life during aging, if not to reduce costs in the healthcare system. Much of the responsibility for a person’s health status rests, though, on the individual: day-to-day decisions about what to eat, in which amount and combination and in conjunction with how much physical activity yield differing degrees of healthy lifestyles. People are increasingly willing to take control of their diets [1,2]. Available options include products with enhanced health properties, such as functional food [3-5] and food supplements .
Supplement users fit a certain sociodemographic profile, e.g. tend to be females, well-educated, and older . In addition, it has been observed that supplement users appear to lead a relatively healthy lifestyle . Thus, they do not necessarily constitute the segment in greatest need of supplements, an observation which is termed the ‘inverse supplement hypothesis’ . The probable cause of this is that consumers motivated and able to lead a healthy lifestyle are more inclined to and capable of adopting supplement usage behaviour. Supplement usage might be related to the increasing popularity of complementary and alternative medicine (CAM), which is driven by the search for a more self-determined and holistic approach to health, well-being and lifestyle [10,11]. However, it has been observed that consumers equate the ‘naturalness’ of e.g. botanical supplements with ‘safety’ , and therefore, at times do not inform their doctors about their supplement use, a fact that has caused concern about adverse health effects [2,12]. A range of factors may influence how consumers view supplements, e.g., the type of product or substance , the perceived relevance of the effect , beliefs and expectations about health outcomes . More general factors might also have an impact on supplement use, such as the prevalence of use in the respective country , or for example, the degree of celebrity use and endorsement . Supplement use or the type of supplement chosen might furthermore be influenced by individual attitudes and interests within the food and health domain, such as the degree of preference for naturalness  or interests in certain food types and dietary trends [3,16]. As the influence of the factors listed above might vary considerably, depending on the substance and the individual in question , there is a need to test the interrelation for specific supplement groups or substances. In addition, psychographic variables have not yet been explored thoroughly in the analysis of food supplement users .
The aim of this paper is to analyse the role of individual characteristics in determining favourable attitudes and adoption intentions toward the resveratrol supplement in two countries, namely the United States and Denmark. Resveratrol is as yet relatively unknown in Denmark, while it is a rather established substance among the food supplement range in the United States (see ), which is why the between-country comparison can shed light on the differences between a developed and an emerging food supplement market. Resveratrol is a substance that may help reduce the risk of chronic diseases such as osteoporosis, cancer and Alzheimer’s disease; it is also said to potentially alleviate the negative effects of obesity, aging and lack of exercise [18-21]. It is a substance naturally found in grapes and wine and has been discussed in relation to the so-called ‘French paradox’ [22,23]. The French paradox is the observation that even though there is a high intake of saturated fats in France, the mortality rate from coronary heart disease is low. This effect was later linked to the traditional diet of the Mediterranean region (i.e., rich in whole-grain cereals, fruits, vegetables, wine, fish, legumes, nuts, and olive oil, and moderate in meat, see ) and might be one of the reasons for the popularity of Mediterranean cuisine. Because of its varying possible effects and associations, resveratrol is a substance especially interesting to study, with regard to how psychographic constructs are related to food-impact health behaviours. In a departure from previous research, the following four research questions are addressed:
Are US and Danish consumers who have favourable attitudes and adoption intentions toward a botanical food supplement containing resveratrol…
… characterised by the same sociodemographic variables as has been found for other supplements or supplements in general (e.g., being female, relatively older, and well-educated)?
… of good health status and behaviour, indicating that the ‘inverse supplement thesis’ applies to the supplement in question?
… expressing favourable health beliefs and behaviours, indicating that they believe in non-medicinal actions (expectations about the health effects of resveratrol, holistic health beliefs, and reporting the use of CAM)?
… characterised by psychographic constructs that can be assumed to explain general favourable reactions to botanicals and more specifically, reactions to resveratrol (e.g., higher interest in natural food, the indulgence dimension of food, and Mediterranean cuisine)?
In the following, we outline the current state of research on the characteristics of supplement users, in relation to each of our four research questions.
Country differences in usage and sociodemographic characteristics of food supplement users
The use of dietary supplements in industrialised countries is said to have increased over the past decades [8,14,25]. In the United States in the 1990s, around 40% of the adult population was found to be regular supplement users, whereas after the turn of the millennium, as many as 73% claimed to have taken supplements during the previous 12 months . Other studies, however, cite statistics such as 40–48%  or 49% (44% male, 53% female ) for the United States during the same time frame. The differences in numbers probably stem from differences in the definition of supplements or the definition of regular supplement use. Findings for Europe, though, generally tend to be lower: in 2001, a national survey in the UK stated that 17% of females use supplements , a representative survey in the Netherlands established that 30% of the respondents claimed to use functional food or a supplement at least once a week , while in Germany, 18% of men and 25% of females used supplements regularly . In Switzerland, however, as much as 41.5% of the population appeared to use supplements . Egan et al. conclude that within Europe, usage is highest in Scandinavian countries and lowest in the Mediterranean, citing results of the EPIC study that found the average share of users ranges from 2–52% among men and from 7–66% among women .
With regard to the sociodemographic profile of supplement users, it is rather established that females are overrepresented among supplement users [8,9,25-28]. In addition, results tend to show that higher age , higher education  and higher income characterise supplement users , as Egan et al. also concluded in their review . However, a study focusing on weight loss supplements in the United States found that users were typically only 25–34 years old and of lower education level , thus strengthening de Jong et al.’s conclusion that characteristics of users depend on the substance in question . Interestingly, a US study indicated that herbs and botanicals are chosen by men in particular , which shows user characteristics might be quite contrary to general findings when focusing on specific supplement types.
Health status and health behaviour of supplement users
Quite a number of authors comment that supplement users tend to exhibit a relatively healthy lifestyle—termed the ‘inverse supplement hypothesis’ - [2,9,13]. De Jong et al. and Beitz et al. found that supplement users indeed showed a healthier eating pattern for specific indicators in the Netherlands and Germany, concluding however that it depends on the substance  and that the healthier eating pattern is not related to a difference in energy intake, but rather, to a difference in food composition . Van der Horst et al. found evidence for the inverse supplement thesis in Switzerland, but at the same time also found support for the opposing hypothesis, because some supplement users were consuming a significantly less healthy diet . In addition, they observed supplement users being relatively less health conscious . This suggests that, apart from user characteristics depending on the supplement substance in question, user groups of the same product might differ in the role that they attach to supplements—as a ‘remedy’ against their existing unhealthy eating patterns or as one of many features of their healthy eating pattern.
Health beliefs and potential psychographic characteristics of supplement users
It is interesting to note that users of complementary and alternative medicine (CAM) are similarly characterised as food supplement users and tend to be female, well-educated, and relatively older . Considering the similarity of the role of CAM and of supplements—both supporting health in a ‘soft’ way and acknowledging the close ties between nutrition, well-being and health - users of CAM and supplement users can be expected to overlap in their psychographic profile to some extent. It has been found that users of CAM hold strong beliefs about the influence of psychological factors (e.g. ‘state of mind’, stress, well-being ) on health. Only a few studies extended research on supplement users to a range of psychological measures and influence factors . An example is an Australian study by Conner et al., who positively tested the explanatory value of the theory of planned behaviour . It has been found that CAM users exhibit modern health worries , including worries about genetic modification and pesticides. Modern health worries, in turn, were found to be related to interest in the naturalness of food [29,30], and consumers tend to prefer ‘naturalness’ in foods more than in medicine . Food supplements and botanicals are perceived as playing a role between both of these, and the role of consumer preference, for naturalness in supplements specifically, is not well known. Furthermore, the indulgence aspect of food might play a role in psychological ‘well-being’, which, in the holistic view of food and health relations, is supposed to impact health.
Research on resveratrol and on botanicals in general
Little research can be found on consumer behaviour in relation to resveratrol, whether as a substance in a supplement or in a food product. To our knowledge, the only study published is one by Barreiro-Hurlé et al. The authors analysed Spanish wine consumers’ preferences for resveratrol-enriched wine with the help of a survey and choice test, and identified a willingness to pay a 55% premium for the health-enhancing wine. However, the respondents regarded wine as generally healthy, although few were able to explain why exactly they thought this to be the case . Interestingly, the health benefits of wine appear to be an emerging research area and point of consumer interest [32,33].
A large share of the supplements used consists of vitamins and minerals . An important and growing area, though, are so-called botanicals . Among the different categories of food supplements, resveratrol-containing products are likely to be subsumed under botanicals. Such plant-based supplements have been examined within the scope of an EU research project [7,34]. It is argued that plant-based supplements are more likely to be used by consumers as a means of medication than as a method to improve nutrition, although it is difficult to disentangle the use for one from the other. From a public-health perspective, this fact calls for more intense scrutiny of consumer behaviour and the characteristics of users of this kind of supplement .