Consumption of Dietary Supplements among Working-Age Residents of Lithuania in the Period from 2021 to 2023

Background and Objectives: The aim of this study was to assess the consumption of dietary supplements (DS) among working-age residents of Lithuania from 2021 to 2023 with respect to social and demographic factors and an assessment of personal health. Materials and Methods: Using stratified sampling techniques, this study included three samples of working-age residents (1600 each year, 4800 total). Three surveys were conducted, the distribution of the respondents between groups was compared using the χ2 test. Results: The consumption of DS significantly differed each year and accounted for 78.1%, 71.6%, and 72.7% of the respondents, respectively (p < 0.05). In 2022, the prevalence of the consumption of DS was lower in the majority of social and demographic groups (p < 0.05). In 2023, it was higher among females, younger residents, and those from larger families, who suffered from COVID-19 (p < 0.05). Despite similar changes found in the consumption of DS among those who negatively assessed their health, this group showed more prevalent consumption of DS among residents with non-university education, unemployed respondents, and those with lower income (p < 0.05). Conclusions: Despite a significantly lower prevalence in the consumption of DS in 2022, it was higher again in 2023. The assessment of personal health shows different habits in the consumption of DS.


Introduction
When nutrition does not meet recommendations, dietary supplements may help correct micronutrient deficiency and maintain adequate intake [1].On the other hand, overconsumption of dietary supplements should be avoided because of possible adverse health effects [2], especially those triggered by food supplements purchased illegally [3].However, researchers bring to light a lack of awareness of these products observed among their consumers [3,4].Major determinants of the consumption of dietary supplements include not only personal factors such as sociodemographic characteristics, older age, perceived benefits of dietary supplements, the history of illness, physiological conditions, and lifestyle factors, but also socio-economic factors like subjective norms, the price of food, and commercial considerations of the sectors involved in the production and sale of dietary supplements [2,5].Attention should be drawn to the fact that dietary supplements are most commonly taken by people with no clinical signs or symptoms of deficiency [1], especially those with an interest in physical performance.Moreover, consumers of dietary supplements tend to have a better overall diet quality with their nutrient intake from foods that most commonly meet the recommended intake levels [1,6,7].
Multiple studies have shown that the COVID-19 pandemic had a significant impact on the prevalence of the consumption of dietary supplements [8][9][10][11].Even though some of them revealed an increase in consumption [8][9][10], there were studies highlighting a decrease in the prevalence of the consumption of dietary supplements [11].In addition to this, it was found that during the COVID-19 pandemic, the perceptions of dietary supplements changed.If, before the pandemic, dietary supplements were associated with healthcare and life cycle-related topics, for example, pregnancy, after the COVID-19 pandemic, consumer interests have shifted to disease prevention [12].
Despite the fact that sex, age, education, place of residence, marital status, number of family members, presence of children in the family, employment, income, COVID-19 cases in a family, and food selection criteria were analyzed as determinants of the nutritional habits and consumption of dietary supplements in previous studies, there is a lack of country-representative studies on the ongoing trends in the consumption of dietary supplements after the COVID-19 pandemic.There is an insufficient level of research carried on DS consumption among diverse social and demographic groups, especially among those with a negative assessment of personal health.After taking into account the inequalities in the consumption of dietary supplements and the occurrence of unequal changes in consumption during the COVID-19 pandemic [8], the aim of this study was to assess the consumption of dietary supplements among working-age residents of Lithuania in the period from 2021 to 2023 with respect to social and demographic factors and the assessment of personal health.

Procedure of Data Collection
The data for this study were collected after conducting three independent crosssectional surveys in October and November of 2021, in October and November of 2022, and in October and November of 2023.A representative sample of adults aged 18 to 64 was formed each year.The multistage stratified probabilistic sampling method was used to select participants for this study.It ensured an equal probability for every household in the country to be surveyed, and, according to target criteria (sex, age, municipality, education, income, employment, marital status), the sample represented the general population of working-aged citizens of Lithuania.Data was collected by conducting an internet-based survey.Random samples of citizens were formed according to the Registry of Residents of Lithuania.Every selected resident received an invitation to participate in this study with a link to the anonymous questionnaire by email.The participants of this study filled out the questionnaire by themselves at a time that was convenient to them.It was possible to fill out the questionnaire only once.Only working-aged citizens of Lithuania were included in this study.This study did not include refugees and other people without Lithuanian citizenship.
Each of the samples independently included 1600 residents.The design of this study was not longitudinal.No data about the inclusion of the respondents in more than one sample were collected.In total, the answers of 4800 respondents are analyzed in this paper.
The comparison of the consumption of dietary supplements before the COVID-19 pandemic with the data collected during the first survey in 2021 has already been published [8].The current paper focuses on the post-pandemic period and the analysis of the prevalence of the consumption of dietary supplements with respect to the subjective assessment of personal health, which had not been covered in our previous paper.
This study was reviewed by the Vilnius Regional Ethics Committee for Biomedical Research.

Description of the Questionnaire
Each of the three surveys was carried out using the same questionnaire with a minimal adaptation for the post-pandemic period.An anonymous questionnaire included questions about the social and demographic characteristics of the respondents, the COVID-19 cases in respondents' families or among friends, their subjective assessment of personal health, nutrition, consumption of food supplements and physical activity.The questionnaire was formed on the basis of the previously used questionnaire about nutrition and consumption of food supplements [13].In this paper, we present the analysis of the questions included in the questionnaire (    Two of the questions regarding the respondents' age and place of residence were open-ended.To achieve an unambiguous interpretation of the results, we transformed them into a binary format.Respondents were asked to identify the municipality they live in.Respondents from 5 municipalities with the largest number of residents were assigned to the "City" group, while the remaining respondents were attributed to the "Towns and villages" group.The age was categorized by median to the range up to 41-year-olds and from 42-year-olds.All other questions were closed.Respondents with primary or secondary education and high school graduates were assigned to the "Nonuniversity education" group.Respondents with unfinished or finished university studies were assigned to the "University education" group.In terms of employment status, the "Employed" and "Unemployed" groups were created.Heads of companies or departments, office workers, civil servants, service sector employees, sellers, workers, and farmers were assigned to the "Employed" group.Retirees, housewives, persons on parental leave, nonemployed persons and students were categorized into the "Unemployed" group.The variable representing an income per member of a family was transformed into a binary format with "Higher income" and "Lower income" categories.With respect to a salary increase, the cut-off point for those groups was 350 EUR in 2021, 400 EUR in 2022, and 470 EUR in 2023.In addition to this, more binary variables were created, such as the number of family members, marital status, and children under 18 years old.The categorization of the rest of the questionnaire is presented in Table 2.

Statistical Analysis
The normality of the variable representing the age of respondents in general samples was tested using the Kolmogorov-Smirnov test with Lilliefors significance correction.This test showed non-normal distributions.Therefore, medians with an interquartile range (Q1-Q3) were presented for this variable.The Pearson's chi-squared test (χ 2 ) was used to determine whether there was a statistically significant difference between the expected frequencies and the observed frequencies in one or more of the categories.Differences were considered statistically significant when the p-value was lower than 0.05.

Results
In total, this study included 4800 respondents: 1600 in 2021, 1600 in 2022 and 1600 in 2023.The median age in the samples collected in 2021 and 2022 was 42 (29-54) years, while in the sample of 2023 it was 43 (30-54) years.The majority of the respondents were employed, married (or with partners), from small towns or villages, with university education, and without children under 18 years old.The samples were similar in terms of sex, age, education, type of place of residence, children under 18 years old, employment status, income, and the subjective assessment of personal health (p > 0.05).The sample collected in 2022 compared to that in 2021 included relatively more single respondents and those who selected foods following other than strengthening health criteria (p < 0.05).In comparison to the 2022 sample, the 2023 sample included relatively more married (or with partners) respondents and those who selected foods with the aim of strengthening of their health (p < 0.05).The distribution of the respondents by social and demographic factors is presented in Table 2.
In 2021, the consumption of dietary supplements was prevalent among 1240 (78.1%) respondents.In 2022, the prevalence of the consumption of dietary supplements significantly lowered and accounted for 1131 (71.6%) subjects (p < 0.001).In 2023, compared to 2022, a higher prevalence of the consumption of dietary supplements was observed: 1163 (72.7%) respondents indicated the consumption of dietary supplements (p = 0.044).Nevertheless, the distribution of the respondents by the majority of purposes for the consumption of dietary supplements remained similar (p > 0.05).The consumption of dietary supplements with the aim of protection against the COVID-19 infection in 2023 was significantly lower than in the previous years (p = 0.004) (Table 3).
The comparison of the prevalence of the consumption of dietary supplements between the three samples revealed the differences within all social and demographic groups (p < 0.05) except for the respondents with children under 18 years old, unemployed respondents, those with lower income, those who indicated health strengthening as the main criterion for the selection of foods, and those who suffered from the asymptomatic or mild form of COVID-19 (p > 0.05).In 2022, the lower prevalence of the consumption of dietary supplements was observed in almost all social and demographic groups: among males, females, employed, younger and older residents of Lithuania, those with and without university education, those from big and small municipalities, those with and without a partner, from families of at least two members, without children, with lower and higher income, those who selected their foods for other than health strengthening criteria, those with and without COVID-19 cases in their families, those who suffered from a severe form of COVID-19, and those who assessed their health positively or negatively (p < 0.05).In terms of the prevalence of the consumption of dietary supplements, the samples of 2021 and 2022 did not differ among the respondents of one-person families, those with children under 18 years old, those who suffered from the asymptomatic or mild form of COVID-19, and those who indicated health strengthening as the main criteria for the selection of foods (p > 0.05).In 2023, no difference in the prevalence of the consumption of dietary supplements was found within all social and demographic groups (p > 0.05), except for a higher prevalence among females, younger residents of Lithuania, those from families with two or more members, those who suffered from COVID-19, and those who suffered from a severe form of COVID-19 (p < 0.05) (Table 4).In at least two of the samples, a higher prevalence of consumption of dietary supplements was observed among females, those with university education, those from larger municipalities, employed respondents, those with higher income, those who suffered from COVID-19, and those who indicated health strengthening as the main criteria for the selection of foods (p < 0.05) (Table 4).
The comparison of the prevalence of a negative assessment of personal health between the three samples revealed no difference (p > 0.05) within all the social and demographic groups except among females, residents from smaller municipalities, adults with lower income, and those who suffered from the asymptomatic or mild form of COVID-19 (p < 0.05).In 2022, a higher prevalence of a negative assessment of personal health was observed among employed respondents and those with lower income (p < 0.05).A lower prevalence was observed among those who suffered from the asymptomatic or mild form of COVID-19.In 2023, a higher prevalence of a negative assessment of personal health was observed among females and those who suffered from the asymptomatic or mild form of COVID-19 (p < 0.05) (Table 5).In at least two of the samples, a higher prevalence of the negative assessment of personal health was observed among older, unemployed respondents, those with non-university education, without children, with lower income, and those who indicated other than health strengthening as the main criteria for selecting foods (p < 0.05) (Table 5).
After comparing the prevalence of the consumption of dietary supplements among those who negatively assessed their personal health between the three samples, the differences were observed among males, older, employed respondents, those with non-university education, without children, those from families consisting of two or more members, those who indicated health strengthening and other criteria as the main criteria when selecting foods, and those with various forms of COVID-19 (p < 0.05).Among those who negatively assessed their personal health in 2022, a significantly lower prevalence of the consumption of dietary supplements was observed among males, older, employed respondents, those with non-university education, residents from cities and smaller municipalities, those with and without a partner, those from families with two or more members, those with and without children under 18 years old, those who indicated other than health strengthening as the main criteria for the selection of foods, and those who suffered from a severe form of COVID-19 (p < 0.05).Among those who negatively assessed their personal health in 2023, no difference in the prevalence of the consumption of dietary supplements was found compared to the previous year (p > 0.05), except for a higher prevalence among those who suffered from a severe form of COVID-19 and those who indicated strengthening of health as the main criterion for the selection of foods (p < 0.05) (Table 6).* a significant difference (p < 0.05) between all the three samples (2021, 2022 and 2023); ˆa significantly higher prevalence (p < 0.05) compared to the sample collected one year before (2021 vs. 2022, 2022 vs. 2023); @ a significantly lower prevalence (p < 0.05) compared to the sample collected one year before (2021 vs. 2022, 2022 vs. 2023); a -a significantly higher prevalence within the sample (p < 0.05); b -a significantly lower prevalence within the sample (p < 0.05).
In at least two of the samples, among the respondents who assessed their health negatively, a higher prevalence of the consumption of dietary supplements was observed among older respondents, those with non-university education, unemployed respondents, those with lower income, those who suffered from a severe form of COVID-19, and those who indicated other than health strengthening as the main criteria for the selection of foods (p < 0.05) (Table 6).
In all three samples, the top six reasons for the consumption of dietary supplements among the respondents who assessed their health negatively were strengthening the immune system, the overall strengthening of the body, strengthening the cardiovascular system, strengthening the bones and joints, boosting the nervous system, and improving digestion.Except for the lower prevalence of the consumption of dietary supplements with the aim to strengthen the cardiovascular system in 2022 (p < 0.05), the distribution pattern of the respondents who assessed their health negatively by purpose for the consumption of dietary supplements was similar in all three samples (p > 0.05) (Table 7).
In all three samples, the consumption of dietary supplements for better digestion was more prevalent among those who assessed their health negatively in comparison to those who assessed their health positively (p < 0.05).This trend was also observed with dietary supplements for the regulation of sleep and boosting the nervous system in 2021 and 2022, as well as for strengthening the cardiovascular system in 2021 (p < 0.05).A lower prevalence of dietary supplements for the overall strengthening of the body among those who assessed their health negatively was observed in 2023 (p < 0.05).No association between the consumption of dietary supplements for other purposes and the subjective assessment of personal health was observed (p > 0.05) (Table 7).
The distribution of the respondents by the consumption of exact supplements was similar in 2022 and 2023.This was observed among the whole sample of consumers and in a subgroup of those who assessed their health negatively.The most prevalent dietary supplement was vitamin D.Moreover, highly prevalent were the complexes of vitamins and minerals: magnesium, vitamin C, omega-3 fatty acids, vitamins of the B group, and fish oil.Other dietary supplements were two or more times less prevalent (Table 8).In 2022, among the respondents who assessed their health negatively, the consumption of B-group vitamins, other vitamins (other than those listed in Table 7), magnesium potassium was higher than among those who assessed their health positively (p < 0.05).In 2022, the consumption of selenium was lower among those who assessed their health negatively (p < 0.05).In 2023, no association between the subjective assessment of personal health and the consumption of exact dietary supplements was observed (p > 0.05).Also, the distribution of the respondents who assessed their health negatively by the consumption of exact supplements was similar to that observed in 2022 (p > 0.05) (Table 8).

Discussion
This study revealed the change in the prevalence of the consumption of dietary supplements among the working-age residents of Lithuania in the period from 2021 to 2023, covering the end of the COVID-19 pandemic and two years later, including the period of the wide-scale war in Ukraine.The results of this study revealed changes in the consumption of dietary supplements in many social and demographic groups, as well as in a subgroup of those who negatively assessed their personal health.Taking into account such a period of time, to our knowledge, up to this date, this study is the first published country-representative study of this topic.
Our results revealed that the prevalence of the consumption of dietary supplements was significantly lower in 2022, after the COVID-19 pandemic, when a wide-scale war in Ukraine began.Results of the 2023 survey showed the stabilization of the prevalence of the consumption of dietary supplements and even a higher prevalence of consumption among females, younger residents of Lithuania, and those from families with at least two members.The post-pandemic decrease in the prevalence of the consumption of dietary supplements was expected in advance because a study conducted in Poland showed that the prevalence of consumption was likely to decrease during the third wave of the pandemic [9].Despite the decrease, the prevalence of consumption in 2022 and 2023 was higher than in 2017 and 2019 [8,14].
Despite the lower prevalence of consumption of dietary supplements in 2022, our study revealed that there were several social and demographic groups where no significant changes in the prevalence of consumption of dietary supplements were observed.These included respondents from one-person families, those with children under 18 years old, and those who indicated health strengthening as the main criteria for the selection of foods.Other researchers emphasize additional factors, such as the Russian-Ukrainian war, that could impact nutrition in the post-pandemic period, which caused a socioeconomic crisis [15].Socioeconomic factors, as shown in other studies, are important determinants for the consumption of dietary supplements [2].
Contrary to the findings of other researchers, our study revealed no significant difference in the prevalence of consumption of dietary supplements between those with positive and negative assessments of personal health [7].The higher prevalence of the consumption of dietary supplements was observed only during the pandemic, in 2021, but not in the postpandemic period.What is more, our study revealed opposite tendencies in the prevalence of consumption of dietary supplements among those with negative assessments of their personal health.While in the general population the prevalence was higher among females, those with university education, those from larger municipalities, employed residents, those with higher income, and those selecting foods with the aim of health strengthening, among the residents with negative assessment of their personal health, a higher prevalence in the consumption of dietary supplements was observed among older adults, those with non-university education, unemployed residents, those with lower income, and those selecting foods according to other than health strengthening criteria.These results seem to be contradictory to the findings of other researchers, who presented that lower socio-economic status is associated with more frequent inadequacy of dietary supplements [16].Unfortunately, we were not able to assess the actual nutrition of the participants of our study; subsequently, we were not able to assess the adequacy of an intake of dietary supplements.Notably, the improvement of health [17][18][19], advertising [20], and other factors [2] are presented as important determinants for the consumption of dietary supplements by other researchers.However, concerns about the inadequate consumption of dietary supplements have been raised for quite some time [21].
Similar to our results, other studies also show a high prevalence of consumption of dietary supplements containing vitamin D, multivitamins, vitamin C, omega-3 fatty acids, probiotics, and zinc [22,23].In our study, the prevalence of these dietary supplements was observed in the general samples also in the subgroups of respondents with a negative assessment of personal health.However, these subgroups presented several differences.Despite a few other mismatches, different from the general population, those with a negative assessment of their personal health more frequently selected dietary supplements for better digestion, regulation of sleep and boosting the nervous system.Despite the fact that only in 2021, a significantly higher prevalence of the consumption of dietary supplements for strengthening the cardiovascular system was observed among those with a negative assessment of their personal health, in 2022, such group of respondents more frequently consumed magnesium and potassium, as well as the B-group vitamins.These findings possibly show the necessity to adapt or specifically target nutrition education and health promotion interventions according to the assessment of personal health [24].

Limitations
We were able to assess only the subjective views of the respondents on the consumption of dietary supplements because of the cross-sectional design of the study.A longitudinal study would have allowed us to objectively assess the changes in consumption of dietary supplements at an individual level.In addition, this would have allowed us to use more advanced statistical methods to predict the change in the consumption of dietary supplements.On the other hand, this study included three country-representative samples, which were larger than sufficient to assess the consumption of dietary supplements among adult residents of Lithuania.
Also, in order to simplify the presentation and interpretation of the results, we converted the age-representing variable into binary.Despite the fact that it revealed some significant differences in the consumption of dietary supplements, in the upcoming studies, it would be beneficial to perform a more detailed analysis because such conversion might hide some subgroups that might significantly differ from each other.
Despite the fact that we analyzed the consumption of dietary supplements with respect to many social, demographic and health-related factors, there might be important factors that were not included in our analysis.

Conclusions
In comparison to 2021, among working-age Lithuanian residents, the prevalence of the consumption of dietary supplements was significantly lower in 2022, when the COVID-19

Table 1 .
Questions about the consumption of dietary supplements included in this study.

Table 2 .
Distribution of the respondents by social and demographic factors.

Table 3 .
Distribution of the respondents by purpose for the consumption of food supplements and the consumption within the past 12 months in the three samples.

Table 4 .
Distribution of the respondents who indicated the consumption of dietary supplements by social and demographic factors in the three samples.

Table 5 .
Distribution of the respondents who assessed their health negatively and social and demographic factors in the three samples.
@ a significantly lower prevalence (p < 0.05) compared to the sample collected one year before (2021 vs. 2022, 2022 vs. 2023); a -a significantly higher prevalence within the sample (p < 0.05); b -a significantly lower prevalence within the sample (p < 0.05).

Table 6 .
Distribution of the respondents who indicated the consumption of dietary supplements and negatively assessed their health by social and demographic factors in the three samples.

Table 7 .
Distribution of the respondents who negatively assessed their health by purpose for the consumption of food supplements in the three samples.

Table 8 .
Distribution of the respondents by the consumption of exact dietary supplements in the samples of 2022 and 2023, with respect to a subjective health assessment.