Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Original article 60 ABSTRACT Secular trends in body height and body mass serve as critical indicators of a population's nutrition, health, and overall well-being. This comprehensive study delves into the anthropometric data of Slovenian young adults spanning a remarkable 65-year period, comparing these findings with secular trends observed in other populations. Data acquisition was accomplished through the utilization of the SLOfit system and the integration of earlier research studies in Slovenia. Height and body mass measurements were collected employing standardized methodologies. Generalized Additive Models for Location, Scale, and Shape (GAMLSS) were harnessed to derive centile curves and establish reference values. Slovenian males consistently grew taller than females, reaching their peak in 2019. Young Slovenian adults continue to grow taller and gain more body mass, with substantial changes in recent years. The largest changes in body mass in both males and females occurred in years between 2015 and 2019, with wider spreads in mass centiles in these years compared to the beginning of the observed period. Healthcare and diet improvements likely contributed to increased body mass, yet sedentary lifestyles and altered diets may also be involved. This research enhances our understanding of environmental, and socio-economic factors in human growth, with implications for public health policies and long-term planning. While this study spans 65 years, it faces limitations in measurement consistency and demographic data. Future research should explore region-specific influences on these trends. In conclusion, monitoring secular trends in body height and body mass is crucial for evidence-based policymaking, health planning, and public health interventions, enabling the promotion of healthy lifestyles and the proactive management of emerging health challenges. Keywords: secular trends, body height, body mass, young adults, Slovenia 1Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia 2Biotechnical faculty, University of Ljubljana, Ljubljana, Slovenia IZVLEČEK Sekularni trendi telesne višine in telesne mase služijo kot pokazatelji prehranjenosti, zdravja in splošnega dobrega počutja prebivalstva. Ta obsežna študija se pogloblja v antropometrične podatke slovenskih mladih odraslih v 65- letnem obdobju in primerja te ugotovitve s sekularnimi trendi drugod po svetu. Podatke smo črpali iz sistema SLOfit in jih integrirali s prejšnjimi raziskavami narejenimi na Biotehnični fakulteti. Meritve višine in telesne mase so bile zbrane z uporabo standardiziranih metodologij. Splošni aditivni modeli (GAMLSS) so bili uporabljeni za izpeljavo centilnih krivulj in določitev referenčnih vrednosti. Ugotovili smo, da so slovenski moški skozi leta vedno višji in da so dosegli vrhunec rasti v letu 2019. Največje spremembe v telesni masi tako pri moških kot pri ženskah so se zgodile v letih med 2015 in 2019, z večjimi razmiki v centilih telesne mase v teh letih v primerjavi z začetkom opazovanega obdobja. Izboljšave zdravstvene oskrbe, boljše prehrane in bolj pogost sedentarni način življenja, so verjetno prispevali k povečani telesni masi slovenskih mladih odraslih. Ta raziskava izboljšuje naše razumevanje okoljskih in socialno-ekonomskih dejavnikov v človeški rasti. Čeprav ta študija traja 65 let, se sooča z omejitvami glede doslednosti meritev in demografskih podatkov. Prihodnje raziskave bi morale raziskati vplive posameznih regij na te trende. Skratka, spremljanje sekularnih trendov v telesni višini in telesni masi je ključnega pomena za oblikovanje politik, ki temeljijo na zdravstvenemu načrtovanju in javnozdravstvenih intervencijah, kar pa omogoča promocijo zdravega načina življenja in proaktivno obvladovanje nastajajočih zdravstvenih izzivov. Ključne besede: medgeneracijske spremembe, telesna masa, telesna višina, mladi odrasli, Slovenija Corresponding author*: Vedrana Sember Faculty of Sport, University of Ljubljana, 1000 Ljubljana, Slovenia E-mail: vedrana.sember@fsp.uni-lj.si https://doi.org/10.52165/kinsi.30.1.60-81 Vedrana Sember 1,* Gregor Jurak 1 Petra Golja 2 Bojan Leskošek 1 Gregor Starc 1 Tatjana Robič Pikel 2 SECULAR TRENDS IN BODY HEIGHT AND BODY MASS OF SLOVENIAN YOUNG ADULTS FROM 1954 TO 2019 SEKULARNI TRENDI TELESNE VIŠINE IN TELESNE MASE PRI SLOVENSKIH MLAJŠIH ODRASLIH MED LETI 1954 DO 2019 Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 61 INTRODUCTION The phenomenon of secular trends in body height and body mass are widely acknowledged as a pivotal indicator of population nutrition, health, and overall well-being (Cole, 2003). Examining these trends yields valuable insights into the evolution of human body composition at the population level (Zhang et al., 2019). The variations seen in body growth can partly be explained by differences in living conditions and the availability or allocation of resources. (Malina et al., 2011). Such disparities can be attributed to a range of factors, also including genetics (Lauby-Secretan et al., 2016) but are hugely determined by environmental conditions (Dubois et al., 2012), socioeconomic status (Öberg, 2014), health status, and the complexity of nutrition (Tanner, 1992). In this regard the steady increase in body height and body mass worldwide can be attributed to lifestyle changes and socioeconomic conditions (Kuh et al., 1991; Marmo et al., 2004; Padez, 2003; Prebeg, 1998; Rodriguez-Martinez et al., 2020a; Thomas & Frankenberg, 2002). This phenomenon, referred to as the secular trend in body height, has led to successive generations surpassing their predecessors (Malina, 1990). The pace and timing of this phenomenon exhibit considerable variation across different countries (Bentham et al., 2016). While most European populations have witnessed a noticeable surge in average body height (Carrascosa et al., 2004; Garcia & Quintana-Domeque, 2007; Roczen Kirsten, 2000), past decades’ studies indicate that this upward trend has plateaued in certain countries, such as Germany (Zellner et al., 2004), Poland (Krawczynski et al., 2003) and Denmark (Schönbeck et al., 2013). This stagnation in body height increase is attributed to either a cessation in socioeconomic advancement or the population attaining their maximum genetic potential in these regions. In contrast, Asian countries continue to experience growth at varying rates (Bentham et al., 2017; Bents et al., 2018). The long-term pattern of body growth has shown an upward direction over the past two centuries (Bodzsar, 1998; Roche, 1979; Tanner, 1966; Van Wieringen, 1986), nevertheless with notable interruptions during periods of crisis in Europe, such as World War I and II (de Muinck Keizer-Schrama & Mul, 2001). Situated at the nexus of pivotal European cultural and trade routes, Slovenia has long been a focal point of strategic interests for major European powers, resulting in a diverse genetic pool (Fertil, 2010; Reeves, 1921; Taylor & Gradišnik, 1956). The pre-WWII evidence is scarce, but the most extensive accelerated growth of young adults in Slovenia was recorded in the first two decades after the WWII (Štefančič, 2008). There was also a significant increase in body mass, Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 62 although not proportional to the increase in height (Štefančič, 2008), while the measurements, which took place between 1981/82 and 1991/92, showed a slowing down of the acceleration tendencies (Štefančič, 2008). The availability of cross-sectional data on body height and mass from individual sources over the last few decades enabled the study of secular trends concerning body height and mass across the entire adult population aged 18-74 in Slovenia (Robič Pikel et al, 2023). However, with rare exceptions (Robič Pikel, 2022), these analyses have not specifically addressed the young adult segment of this population in detail for the past century. The present study tries to close this gap by analysing pertinent data regarding the anthropometric parameters of Slovenian young adults over a period of 65 years and contrast them with the secular trends observed in other populations and age cohorts. Additionally, the study aims to ascertain alterations in the amplitude and orientation of secular trends in body height and body mass of Slovenian young adults in the age group of 18-25 years, spanning a period of 65 years. METHODS Data were collected within the SLOfit study of the Faculty of Sport, University of Ljubljana (No. 6-2019-539) and with regular measurements and data collection within the (data) Base of Anthropometric Measurements (BAM) (Golja & Pikel, 2021) at the Department of Biology, University of Ljubljana, approved by the Slovenian National Medical Ethics Committee (KME 104/12/10) and following the Declaration of Helsinki. In the analysis, we used anonymised data. Participants Body height and body mass data between 1954 and 1990 were obtained from measurements at the Biotechnical Faculty of the University of Ljubljana and collected from BAM (Golja and Robič Pikel, 2021), while the after 1990 data were obtained through the SLOfit system for population aged 18 – 25 years. The SLOfit system is a population-based national surveillance system that tracks somatic and motor development of children, youth, and adults in Slovenia on the population level (Jurak et al., 2020, 2022). All available data were merged into a single dataset and Table 1 provides sample sizes of individual measurements from 1950 to 2019. Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 63 Table 1. Sample sizes (N) and mean age of participants [years] (M) separated by sex and year of measurement. Male Female Male Female Year N M N M Year N M N M 1954 264 20,7 183 20,2 1996 5935 18,5 6428 18,5 1955 158 20,9 20 21,0 1997 4884 18,5 4652 18,5 1956 100 20,6 113 20,0 1998 5211 18,5 5054 18,5 1957 131 21,3 145 20,5 1999 4974 18,5 5093 18,5 1958 90 23,3 56 22,4 2000 5058 18,5 4672 18,5 1959 224 20,5 292 19,7 2001 4983 18,5 4786 18,5 1960 224 20,5 194 20,8 2002 5102 18,5 4867 18,5 1961 216 19,7 152 19,9 2003 5036 18,5 5023 18,5 1962 219 21,7 124 21,3 2004 4253 18,5 4202 18,5 1963 197 21,5 104 20,4 2005 4374 18,5 4430 18,5 1964 210 20,4 264 20,4 2006 5693 18,5 5818 18,5 1965 61 21,9 114 21,3 2007 3453 18,5 3918 18,5 1967 41 23,5 33 23,4 2008 3491 18,5 3462 18,5 1969 32 22,8 91 23,0 2009 5297 18,5 5545 18,5 1981 54 20,0 84 19,2 2010 4698 18,5 5534 18,5 1982 203 19,2 179 18,9 2011 4769 18,5 4972 18,5 1983 36 20,0 87 19,9 2012 5628 18,5 5562 18,5 1987 89 20,4 187 19,3 2013 5031 18,5 5374 18,5 1988 188 20,6 142 19,7 2014 5269 18,5 5041 18,5 1990 3611 18,4 5268 18,4 2015 6259 18,7 6543 18,7 1991 3576 18,4 5120 18,5 2016 6246 18,5 6105 18,5 1992 4794 18,5 6326 18,5 2017 6046 18,5 5995 18,5 1993 5118 18,5 6321 18,5 2018 5058 18,5 5291 18,5 1994 6211 18,5 7116 18,5 2019 2559 18,5 2670 18,5 1995 5950 18,5 6578 18,5 Testing and measurements A comprehensive approach was adopted to ensure the use of standardized research tools and the availability of necessary measurement equipment and personnel. Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 64 Testing and measurements at the Biotechnical Faculty A part of the anthropometric measurements was conducted between 1954 and 1990 at the Department of Biology on an annual basis by proficient personnel. Standardized equipment and procedures were applied (Weiner & Lourie 1969, Lohman et al. 1988). Practitioners belonging to three different generations were responsible for taking measurements. Each examiner underwent direct training from their predecessor, ensuring that all measurements were consistently performed following the same procedure. During the measurements, the subjects were barefoot and dressed in light clothing. Body mass was measured with certified calibrated personal scale to the nearest 0.5 kg (a standard physician balance beam scale). Body height was measured with standardized anthropometer to the nearest 0.1 cm according to the following protocol: no shoes were worn, upright stance with subject’s heels together, with subject having relaxed shoulders and back as straight as possible, and with head positioned in Frankfort plane (Kotnik & Golja, 2012). Testing and measurements within the SLOfit system Anthropometric measurements within SLOfit system were performed between 1990 and 2019 in Slovenian high schools. All anthropometric variables were performed by Physical Education teachers, who were extensively trained in anthropometry and SLOfit measurement protocols by the Faculty of Sport. Height was measured to the nearest 0.1 cm with head positioned in Frankfort plane, while body mass was measured to the nearest 100 grams (Kovač, Marjeta, Jurak Gregor, Starc Gregor, 2017). Statistical analyses Centile curves and reference values were obtained using Generalised Additive Models for Location, Scale and Shape (GAMLSS) (Rigby & Stasinopoulos, 2005). Three continuous (Box- Cox Cole and Green [BCCG], Box-Cox power exponential [BCPE], Box-Cox-t [BCT], generalised inverse Gaussian) distributions were fitted to the data as appropriate, optimising the degrees of freedom (DF) for P-splines fit for all parameters of the respective distributions using Schwarz Bayesian criterion (SBC) (Schwarz, 1978). Appropriate link functions were used for the parameters. BCCG is routinely used in the Lambda Mu Sigma (LMS) method (Cole & Green, 1992). BCPE and BCT are extensions of LMS adding an extra parameter, ν, to allow modelling (positive or negative) kurtosis [with ν=2 BCPE and BCCG (LMS) coincide]. The best-fitted model was selected based on SBC, observation of worm plots (Buuren & Fredriks, 2001) and comparison of estimated and empirical centiles. In all the models, λ=0.5 was used Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 65 for the power transformation of age. Separate analyses were performed for males and females. DFs (Degrees of Freedom) for P-splines fit for the extra parameter were optimised, as described previously. The analysis was performed using the R language for statistical computing (R version 3.6.3, R Foundation for Statistical Computing, Vienna, Austria); GAMLSS were fitted using R package gamlss (Stasinopoulos & Rigby, 2007). The best-fitted models with the optimal DFs for the P-splines fit for all parameters of the respective distributions and SBC for each gender are reported in Supplemental files (see Table S1, S2, S3, S4). RESULTS In present study, we examined the body height and body mass of 311634 young adults, comprising of 151304 males and 160330 females, who were measured over a period extending from year 1954 to year 2019. Given the asymmetric distribution observed in our dataset, we opted to present the central tendency and variability of our data in terms of the median (Me) and interquartile range (IQR), respectively. The median age of all participants was found to be 18.48 years. This measure of central tendency was accompanied by an IQR of ±0.53 years, indicating a relatively narrow range of age variability among participants. This pattern of age distribution was consistent across gender subgroups, with males displaying a median age of 18.47 years (IQR: ±0.53 years) and females showing a median age of 18.48 years (IQR: ±0.53 years). These findings highlight the homogeneity in the age distribution of our sample, providing a stable foundation for the subsequent analysis of body height and body mass across the study population. Figures 1-4 present the centile curves for body height and body mass at the 1st (C1), 3rd (C3), 10th (C10), 25th, 50th, 75th, 90th, 97th, and 99th (C99) centiles. Corresponding score values for each of these centiles can be found in the Supplemental files (refer to Table S1, S2, S3, and S4). The results showed that Slovenian males measured in 1954 were the shortest, while those measured in 2019 were the tallest over the 65-year period that we observed (see Table S1). Figure 1 demonstrates that males’ height has almost consistently increased during the observed period. The growth rate slowed down slightly after 1995 and at the end of the observed period, in years between 2015 and 2019 a stagnation or even slight decrease is noticed in lower centiles (C3, C1), e.g. C1 decreased from 164.5 cm in 1995 to 163.4 cm in 2019 (Table S1). Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 66 Figure 1. Body height centile curves for the 1st, 3rd, 10th, 25th, 50th, 75th, 90th, 97th, and 99th centile for males from 1950 to 2019. Similar to males, our analysis revealed that females measured in Slovenia in 1954 were the shortest, while those measured in 2019 were the tallest over the 65-year period that we observed. Figure 2 illustrates that females’ body height has consistently increased each year. Although all the centile curves display a similar pattern of a mostly consistent growth through the observed period, growth was more pronounced before 1995, then it slowed down. At the end of the observed period a stagnation or even slight decrease may be noticed for the lower centiles. E.g. C1 decreased from 152.8 cm in 2000 to 152.0 cm in 2019 (Table S2). If one observes body height centile curves for males, there is a plateauing trend below the 50th centile, whereas young adult males’ body height ranging above 50th centile exhibits continued growth. Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 67 Figure 2. Body height centile curves for the 1st, 3rd, 10th, 25th, 50th, 75th, 90th, 97th, and 99th centile for females from 1950 to 2019. In Slovenia, changes in male body mass are less consistent than in body height (Figure 3). In the median and higher quantiles, body mass generally increases, but not so linearly as in body height. In the lower centiles, a stagnation may be noticed around C10. In the lowest centiles, C1 and C3, after the slight initial growth, the trend reverses to slightly declining. Therefore, variability in body mass steadily increase throughout the observed period, e.g. the difference between C1 and C99 increased from 35.2 kg in 1954 to 58.9 kg in 2019 (Table S3). Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 68 Figure 3. Body mass centile curves for the 1st, 3rd, 10th, 25th, 50th, 75th, 90th, 97th, and 99th centile for males from 1950 to 2019. In female body mass, most of the centile curves are nearly flat from year 1954 through around 2005, when they started to increase in median and upper centiles and stay flat or even decrease in the lower centiles (Figure 4). Therefore, variability in body mass increased rapidly after 2005, e.g. the difference between C1 and C99 increased from 33.3 kg in 1954 to 54.9 kg in 2019 (Table S4) Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 69 Figure 4. Body mass centile curves for the 1st, 3rd, 10th, 25th, 50th, 75th, 90th, 97th, and 99th centile for females from 1950 to 2019. DISCUSSION The aim of the present study was to collect relevant data on the body height and body mass of young adults in Slovenia over the past 65 years and determine changes in the magnitude and direction of secular trends in body height and mass among young adults aged 18 to 25 years in Slovenia. The study showed that both male and female body height has increased over the observed period, which is in accordance with previous reports (Robič Pikel, 2021; Robič Pikel et al., 2023). The centile curves for body height showed a consistent growth across the observed years, with highest variability from 2015 to 2019, as compared to the beginning of the observed period. However, there was a slight decrease in body height for males and females ranking in the first centile in the recent years. Young male adults ranking from the 75th to 99th centiles are still growing, which is suggesting that the growth patterns of males may vary, with those in the higher centiles demonstrating increased height potential. Females body height followed a similar pattern as males’, i.e. constant growth throughout the observed period, with slight stagnation or decline in lower centiles. However, the growth tempo was somewhat slower in females than in males, e.g. the median growth increased by 4.4 cm in Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 70 the observed period, while the males’ median increased by 5.7 cm. Also, differently as in males, all the centiles in females have the highest growth tempo between 1975 and 1990, while in males the highest tempo was near the beginning of observed period and it slowed down significantly after year 2000, except for the highest centile, where it increased again after 2010. The extended growth almost to the end of the observed period of C99 is also present in females but seems to stop after 2015. Furthermorev, it is worth mentioning that the timing and pace of growth also vary between individuals and can be influenced by various environmental factors such as physical activity levels, stress, and overall health status (Silventoinen, 2003). Therefore, the variability in body height among males and females in different centiles may be the result of a complex interplay between genetics, hormonal, and environmental factors (Hills & Byrne, 2010). Both male and female body mass has generally increased over the observed period of 65 years. This increase was more pronounced in the upper centiles and less in lower, e.g. the C99 increased by 25% in both males in females. Increase in body mass slowed down in the lower centiles, and more so in males than females, and even experience negative growth of around 3% in both genders in C1. Although the general trend of body mass was increasing, this growth was not linear: the highest increase in both genders occurred in years between 2005 and 2010. In females between 1975 and 1990, and in males in the 1980s, a significant decrease of body mass was observed with wider spreads in body mass centiles between year 2005 and 2010, as compared to the beginning of the observed period. Young males up to the 90th centile have plateaued in body mass, while young adult males in the 99th centile continue to gain body mass. It is imperative to interpret these observations with the understanding that they represent cross- sectional data from different cohorts at various time points, not longitudinal trends within the same individuals. Young females up to the 75th centile have plateaued, whereas those in the 90th and 99th centiles are still gaining body mass. However, a decline in body mass was seen in the 50th and 99th centile groups between year 1975 and 1990, which could potentially be attributed to the influence of the sample, as it may have been unrepresentative during that time period. The increase in body mass may reflect changes in lifestyle and diet over time, which could have contributed to the observed changes in body mass. The major finding of the study is that in the period of the past 65 years, both sexes of young adults showed an overall increase in body dimensions, which is in line with the findings from Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 71 other researchers (Kalka, Pastuszak, & Buśko, 2019; Mintem, Gigante, & Horta, 2015; Pikel et al., 2023). The body height of students over the period of the past 50 years at the University of Technology Warsaw increased by 8.06 cm, while at Józef Piłsudski University of Physical Education in Warsaw, it increased by 6.90 cm (Kalka et al., 2019). A similar 7.8 cm increase in body height was observed in 19-year-old Polish military recruits from year 1965 to 2010 (Kołodziej et al., 2015), attributed to cultural changes and improved financial status. According to these authors, the results reflected cultural changes and improvement in the financial status of the population, which contributed to more efficient use of the genetically determined growth potential. Furthermore, a study published in The Lancet in 2016 analysed population-based data from 186 countries and reported that the global age-standardized mean body mass index (BMI) increased significantly from 1975 to 2014, with men's average BMI increasing from 21.7 kg/m² to 24.2 kg/m² and women's from 22.1 kg/m² to 24.4 kg/m² (Collaboration, 2016b). The same study reported that the most pronounced increases in body height and body mass across Europe were identified between the 1970s and the 1980s, observing generally parallel upward trends in both height and body mass between genders, however, with more moderate rises in the following decades (Collaboration, 2016b). However, this pattern does not extend uniformly back in time. Specifically, analysis of body height of young adults (approximately 23 years old) born in Great Britain from the early 20th century up to 1958 (Kuh et al., 1991), with a sample size of 50,000, revealed a secular increase in body height at a rate of 1.09 cm per decade for men and 0.36 cm per decade for women. This indicates discernible differences in the magnitude of height increase per decade between genders. While the overarching trend in height and body mass has been upward for both genders, the absolute values of these increases are not identical, underscoring gender-specific variations in growth patterns over the decades. In general, both males and females have experienced increases in height and body mass in Europe over the past few decades, but the trends seem to differ between genders. Studies have consistently shown that males are taller and heavier than females on average, but some of the studies report that the rate of change in height and body mass has been similar between the genders (Collaboration, 2016a). This, however, was certainly not the case, for example, in the Slovenian (Robič Pikel et al., 2023); the present study), Czech (Kopecký et al., 2016), or British (Kuh et al., 1991) populations. Moreover, females from Central-Southeast Europe, including Slovenia, Montenegro, Serbia, and Slovakia, are among the top 10 tallest female populations globally, with Slovenian females notably ranked ninth in height (Popović, 2018). Likewise, four nations stemming from the Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 72 former Yugoslav republics- Montenegro, Bosnia and Herzegovina, Croatia, and Serbia- are recognized among the top 10 countries with the tallest male populations globally (Popović, 2018). Additionally, Albanians, hailing from the same Balkan region, are noted for their body height, ranking among the world's tallest men (Popović, 2018). While physical height is largely heritable (Silventoinen et al., 2021), there may be region-specific factors influencing height trends, above all, the environmental factors, which include the daily diet, the exposure to various infections, as well as the socio-economic status, especially during childhood (Popović, 2018; Subramanian et al., 2011). Understanding these factors can be important for informing public health policies and interventions aimed at promoting healthy growth and development in populations across the globe. Data in present research does not suggest, that Slovenian young adults already reached the overall plateau in both, body height and body mass. Identifying the exact reasons is challenging, as several possible explanations could account for this phenomenon. One possible explanation is that the changes in lifestyle and nutrition patterns (Silventoinen, 2003) in Slovenia have contributed to the continuous increase in body height and body mass among young adults. For instance, potential improvements in healthcare and nutrition may have positively influenced the growth and development of young adults, resulting in continuous increases in body height and body mass over time. Changes in dietary habits, food availability, improvements in living standards, and economic growth, could have contributed to increases in body mass (Lobstein et al., 2015). In addition, sedentary lifestyles, caused by technological advancements and changes in work and lifestyle, can lead to body mass gain due to decreased physical activity (Owen et al., 2010). Prolonged sitting and low activity levels can reduce energy expenditure, increase calorie intake, and cause a positive energy balance, leading to body mass gain. Muscle atrophy and reduced metabolic rate can also result from prolonged sitting, making it more challenging to maintain a healthy body mass (Lee et al., 2012). The identification of causes for the observed trends of body height and body mass of young adults is beyond this study, but the identified trends could in the future be compared with other socio-demographic and economic trends that could explain the growth trends of small populations as the Slovenian one. Namely, the population living in Slovenia experienced very turbulent and diverse changes. The 1970s witnessed transformative urbanization and industrialization processes that altered people's dietary habits and physical activity levels. During this era, there was a substantial increase in worker migration from Bosnia, Serbia, and Montenegro, with the migration numbers doubling between 1971 and 1981. The migration Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 73 number for Bosnians was even more pronounced, with their numbers tripling in the 1990s (Josipovič, 2023; Ravbar, 1990). The transition to a more sedentary lifestyle, coupled with the influx of young workers from the tallest ethnic groups in the Balkans, raises the question of whether these numbers were substantial enough to impact the population's average height in Slovenia (Grasgruber et al., 2022). These workers, who permanently settled and established their families in Slovenia, potentially contributed to demographic changes, yet the extent of their influence on height averages remains a matter for further investigation. Second, the studies of serious economic crisis in former Yugoslavia in the 1980s (Brown, 1997) that reduced access to food, and the inflow of western high-caloric and processed food in the 1990s after the disintegration of former Yugoslavia could also provide more insights in the causes for the trends in body height and body mass we observed in our analysis. Our study provides valuable information for health professionals and policymakers from different areas, who are interested in understanding the effects of biological changes on potential future risks and opportunities. Anthropologists have long been interested in understanding the complex interplay of genetics, nutrition, environmental conditions, and social, economic, and cultural factors that contribute to human conditions. Strengths and limitations We acknowledge several strengths and limitations that must be considered when interpreting our findings. The main strength of this paper lies in the extensive time interval examined, covering 65 years of body mass and body height measurements in Slovenian young adults. However, during the early decades, the reporting of body height and mass relied on rather small samples. It was only from 1990 onwards, that large datasets were used. Furthermore, the anthropometric variables used in the present study were not measured with the same equipment over the years. Since the analysed data did not include specific demographic information such as education level, income, and occupation, and the absence of information on nutritional and movement behaviour or physical fitness, make interpreting of the results more challenging. CONCLUSION Present study explored changes in body height and body mass among young adults in Slovenia over 65 years. Results showed increased body height and body mass, reflecting the impact of improved healthcare and nutrition, but also lower physical activity on growth and development. While the exact reasons for this phenomenon remain unclear, it has occurred due to complex Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 74 and multifactorial interactions. The study contributes to the future research that could focus on how region-specific factors may have influenced the trends in body mass and body height, resulting in the population of Slovenia being among the 10 tallest nations in the World (Rodriguez-Martinez et al., 2020). In its essence, data on secular trends in body height are a valuable tool for evidence-based policymaking and can guide interventions aimed at improving nutrition, health, and overall well-being of the Slovenian population. Policymakers can use the data to inform and shape nutritional policies, because understanding how average body height and body mass change over time can provide insights into the effectiveness of nutritional programs and policies aimed at improving the overall health and well-being. Secular trends may also reflect broader health trends within a population, which can inform the designing of public health interventions based on this data, targeting specific age groups or demographics that may be experiencing challenges related to nutrition, health, or socio-economic factors. Changes in body height and body mass may be associated with socioeconomic factors, and this data can be used to monitor and address socioeconomic disparities that may contribute to variations in body height and body mass outcomes, helping to design more equitable policies. Our findings could also be valuable for long-term health planning. This includes anticipating health needs, allocating resources, and developing strategies to address potential health challenges that may emerge in the future. Lastly, comparative analysis of secular trends in body height and body mass across different populations can provide valuable insights into global health patterns. This information can be used to learn from the experiences of other countries and adapt strategies that have been successful in improving future health risks and opportunities. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. REFERENCES Bentham, J., Di Cesare, M., Bilano, V., Bixby, H., Zhou, B., Stevens, G. A., Riley, L. M., Taddei, C., Hajifathalian, K., Lu, Y., Savin, S., Cowan, M. J., Paciorek, C. J., Chirita-Emandi, A., Hayes, A. J., Katz, J., Kelishadi, R., Kengne, A. P., Khang, Y. H., … Cisneros, J. Z. (2017). 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Year C1 D1 Q1 Me Q3 D9 C99  1954  161.2 167.1 170.7 174.7 178.9 182.8 189.7 1955  161.3 167.2 170.8 174.9 179.0 182.9 189.8 1960  161.8 167.8 171.4 175.4 179.6 183.5 190.4 1965  162.2 168.3 171.9 176.0 180.2 184.1 191.0 1970  162.7 168.9 172.5 176.6 180.8 184.6 191.6 1975  163.2 169.4 173.1 177.2 181.4 185.2 192.2 1980  163.6 169.9 173.6 177.7 181.9 185.8 192.8 1985  163.9 170.4 174.1 178.2 182.4 186.3 193.4 1990  164.2 170.8 174.6 178.7 183.0 186.9 194.0 1995  164.5 171.2 175.0 179.2 183.5 187.4 194.6 2000  164.4 171.3 175.2 179.5 183.8 187.7 195.0 2005  164.1 171.4 175.3 179.6 183.9 187.9 195.3 2010  163.9 171.4 175.5 179.8 184.1 188.2 195.7 2015  163.6 171.5 175.7 180.1 184.5 188.5 196.3 2019  163.4 171.7 175.9 180.4 184.8 188.9 196.9 Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 79 Supplemental Table S2. Average height of included females for first and last centile (C1, C99), decile (D1, D9), quartile (Q1, Q3) and Median (Me). Year C1 D1 Q1 Me Q3 D9 C99  1954 149.3 155.3 158.7 162.5 166.5 170.1 176.9 1955 149.4 155.3 158.8 162.6 166.6 170.2 177.0 1960 149.7 155.7 159.2 163.1 167.0 170.7 177.4 1965 150.0 156.1 159.5 163.4 167.4 171.0 177.6 1970 150.2 156.4 159.9 163.8 167.7 171.3 177.8 1975 150.7 156.9 160.4 164.3 168.2 171.7 178.1 1980 151.3 157.5 161.0 164.9 168.8 172.3 178.6 1985 151.9 158.1 161.6 165.4 169.3 172.8 179.1 1990 152.4 158.6 162.1 165.9 169.8 173.3 179.6 1995 152.8 159.0 162.4 166.3 170.1 173.7 180.1 2000 152.8 158.9 162.4 166.3 170.2 173.9 180.5 2005 152.6 158.8 162.3 166.3 170.3 174.0 180.9 2010 152.5 158.9 162.5 166.5 170.5 174.3 181.4 2015 152.4 159.1 162.8 166.8 170.8 174.6 181.9 2019 152.0 159.1 162.9 166.9 171.0 174.8 181.9 Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 80 Supplemental Table S3. Average body mass of included males for first and last centile (C1, C99), decile (D1, D9), quartile (Q1, Q3) and Median (Me). Year C1 D1 Q1 Me Q3 D9 C99  1954  53.0 58.9 62.5 66.8 71.6 76.7 88.2 1955  53.0 59.0 62.6 67.0 71.8 76.9 88.5 1960  53.6 59.7 63.4 67.9 73.0 78.3 90.2 1965  54.4 60.7 64.6 69.3 74.6 80.2 92.6 1970  54.5 60.8 64.8 69.7 75.3 81.0 93.5 1975  53.8 60.2 64.3 69.3 75.0 80.8 93.3 1980  53.3 59.8 64.0 69.1 74.9 80.9 93.4 1985  53.8 60.5 64.8 70.2 76.3 82.5 95.5 1990  53.5 60.4 64.9 70.5 76.8 83.3 96.8 1995  53.8 61.0 65.7 71.6 78.2 85.1 99.3 2000  53.3 60.8 65.8 71.9 78.9 86.1 101.0 2005  52.7 60.8 66.1 72.6 80.0 87.4 102.8 2010  53.0 61.8 67.6 74.6 82.3 90.2 106.1 2015  51.9 61.2 67.1 74.2 82.2 90.2 107.0 2019 51.4 61.1 67.1 74.4 82.6 91.2 110.3 Kinesiologia Slovenica, 30, 1, 60-81 (2024), ISSN 1318-2269 Body Height and Mass Secular Trends 81 Supplemental Table S4. Average body mass of included females for first and last centile (C1, C99), decile (D1, D9), quartile (Q1, Q3) and Median (Me). Year C1 D1 Q1 Me Q3 D9 C99  1954 45.6 51.0 54.5 58.8 63.7 68.6 78.9 1955 45.6 51.0 54.4 58.7 63.6 68.5 78.9 1960 45.4 50.7 54.2 58.5 63.3 68.3 78.8 1965 45.4 50.7 54.2 58.4 63.3 68.4 79.2 1970 46.3 51.8 55.3 59.7 64.7 69.9 81.2 1975 46.4 51.9 55.4 59.8 64.9 70.2 81.9 1980 45.8 51.2 54.7 59.0 64.0 69.4 81.4 1985 45.5 50.8 54.3 58.7 63.7 69.1 81.5 1990 44.8 50.1 53.6 58.0 63.1 68.6 81.5 1995 44.4 49.9 53.4 57.9 63.2 69.0 83.0 2000 44.0 49.6 53.3 57.9 63.4 69.6 85.0 2005 44.0 49.8 53.6 58.4 64.2 70.8 88.0 2010 44.2 50.4 54.5 59.7 66.0 73.3 93.2 2015 43.9 50.4 54.6 60.1 66.7 74.6 96.8 2019 43.9 50.6 54.9 60.5 67.3 75.4 98.8