The coast of giants: an anthropometric survey of high schoolers on the Adriatic coast of Croatia

The aim of this anthropometric survey was to map regional differences in height and body proportions in eight counties adjacent to the Adriatic coast of Croatia. Body height was measured in 1,803 males and 782 females aged 17–20 years at 66 schools in 23 towns. When corrected for population size in regions, mean male height is 182.6 cm in all eight counties, 182.8 cm in seven counties of Adriatic Croatia, and 183.7 cm in four counties of Dalmatia proper. Regional variation is considerable: from 180.6 cm in the county of Karlovac to 184.1 cm in the county of Split-Dalmacija. The mean height of females is based on more limited data (168.0 cm in seven counties). These results show that young men from Dalmatia are currently the tallest in the world in the age category of 18 years, and the north-to-south gradient of increasing stature on the Adriatic coast largely mirrors that in neighbouring Bosnia and Herzegovina (BiH). The extraordinary values of height in Croatia and BiH can most likely be explained by unique genetic predispositions that are shared by the local populations of the Dinaric Alps.


INTRODUCTION
Our previous study dealing with the stature of young males in Bosnia and Herzegovina (BiH) (Grasgruber et al., 2017) confirmed older reports according to which the people from the Dinaric Alps are one of the tallest in the world. It is obvious that they cannot currently reach their genetic potential due to poverty and a relatively poor quality of their diet, but given the presence of these factors, their height is even more remarkable. The height of young men from Herzegovina aged 17-20 years is 183.4 cm, which is only a slightly lower value than in the wealthy and well-fed Dutch (183.8 cm), who are officially the tallest in the world (Schönbeck et al., 2012). Furthermore, our comparisons indicate that local Muslim (Bosniak) men in Herzegovina are 2-3 cm shorter than Croats and Serbs living in the same regions or even the same towns. These differences in height are very strongly associated with the regional production of pork. Because pork is absent in the diet of Muslims for religious reasons, this result independently confirms the key role of high-quality nutrients from pork in child nutrition, as can be seen from our previous ecological studies (Grasgruber et al., 2014;Grasgruber et al., 2016).
These data strongly suggest that the Dalmatian phenomenon is only a regional anomaly and height decreases rapidly in the northern direction towards mainland Croatia. Indeed, historical data show that the average Croatian recruit around 1883 was 165.5 cm tall (Komlos, 2007), but height on the Adriatic coast ranged from 166 cm in Istria to 171 cm in southernmost Dalmatia (Coon, 1939). A large nationwide survey of school children performed in Croatia between 1980-1984 in 36 towns/areas showed that these differences had persisted even after 100 years (Prebeg, 1988). At the age of 18 years, the height in some coastal and mainland regions differed by 4-5 cm. The shortest high schoolers came from the region of Zagorje north of Zagreb. To our knowledge, no later anthropometric survey used sufficiently representative samples of young males and females from the whole territory of Croatia. Therefore, mapping these geographical differences constitutes an intriguing challenge and the Adriatic coast is a particularly interesting territory in this regard.
Geographically, Adriatic Croatia is divided into two halves, which are separated by the mountain ranges of Velebit and Kapela. These mountains are a continuation of the main ridge of the Dinaric Alps in BiH and run through the rocky and sparsely inhabited county of Lika-Senj. They also separate the whole Adriatic coast from mainland Croatia. The region south of this mountain range is traditionally considered as 'Dalmatia proper' and consists of four counties (Zadar, Šibenik-Knin, Split-Dalmacija and Dubrovnik-Neretva), which include 0.86 milion people (20% of the total Croatian population) (Croatian Bureau of Statistics, 2013a).
Although Dalmatia has a very pleasant Mediterranean climate, it has suffered from severe deforestation since the Neolithic (Kranjc, 2009), which led to the creation of an unhospitable 'limestone desert' covered by grass and bush. The local population has historically relied on pastoralism and at present, the inland Dalmatia is characterized by high rates of emigration for economic reasons. Furthermore, during the war events 1991-1995, ethnic tensions in the counties of Šibenik-Knin, Zadar, Lika-Senj and Karlovac led to the displacement of the local Serbian population. After the end of the war, the areas experienced an influx of Croatian (Catholic) refugees from BiH.
Because of these ongoing population changes, our research is one of the last opportunities to capture the original distribution of anthropological characteristics in this region. We were particularly interested in whether the north-to-south height gradient follows that documented in BiHfrom 180.0 cm in Canton Una-Sana to 184.5 cm in the region of Trebinje. Therefore, we decided to include the whole area of coastal Croatia adjacent to the border of BiH.

METHODS
The research on the Adriatic coast of Croatia is a part of a larger anthropological project started in collaboration with the University of Montenegro in 2015. The aim of this project is to provide detailed mapping of body height and some other anthropological characteristics on the territory of the Dinaric Alps, which would enable better understanding of this intriguing phenomenon. At present, this project already covers Bosnia, Herzegovina, Croatia, Montenegro and Kosovo. In addition, preliminary measurements of university students were performed in Albania during the year 2017. The survey in Montenegro will be repeated in 2018.
The present study was realized within the project "Anthropological research of sports potential in Dalmatia", number MUNI/A/1090/2016, with the support of the Specific University Research Grant, as provided by the Ministry of Education, Youth and Sports of the Czech Republic in the year 2016. Its primary objective was to measure body height and some body proportions (sitting height, arm span) on the territory of Adriatic Croatia, as defined by the Croatian Bureau of Statistics (Narodne novine, 2012). This region consists of seven counties (županijas): Istra, Primorje-Gorski Kotar, Lika-Senj, Zadar, Šibenik-Knin, Split-Dalmacija a Dubrovnik-Neretva. Total population in these seven counties is 1.41 million (33% of the total Croatian population) (Croatian Bureau of Statistics, 2013). Because the counties of Primorje-Gorski Kotar and Lika-Senj are largely separated by the mainland county of Karlovac, we also decided to include the latter to have a more complete picture ( Fig. 1). The eight counties together comprise 1.54 million people (36% of the total Croatian population).
Target population. The target population consisted of high schoolers (3 rd and 4 th graders) aged 17-20 years. Similar to our previous study in BiH, we always tried to measure the broadest spectrum of schools, from vocational to elite high schools (gimnazija). Our general goal was to incorporate sufficiently representative samples of ≥ 200 individuals from each region. For organizational or time reasons, it was not always possible to measure a sufficiently large sample of both sexes and hence we again concentrated mainly on males. The same limitations infuenced the measurement of body proportions. Data collection. The research was performed between April 2015-May 2017. Very few of the schools contacted refused to participate, which allowed us to meet most of our goals. The measurements were conducted using two devicesa mobile stadiometer SECA 213 and a specially constructed apparatus designed for the measurement of height, sitting height and arm span. The mutual compatibility and accuracy of these devices was tested on a sample of 91 Czech high schoolers. The mean difference in the measured height was only 1.5 mm (180.10 vs 180.25 cm).
Before the measurements, the students completed a short questionnaire, which included an informed consent agreement and questions about date of birth, place of residence and the level of education of the students' parents. The results obtained during the survey were subsequently analyzed using the software Statistica 12. The values of height for each sample included means, standard deviations, medians, a range of extreme values, skewness, kurtosis and tests of normal distribution (Kolmogorov-Smirnov, Lilliefors and Shapiro-Wilk).

RESULTS
The research included measurements of body height in 1827 males and 792 females at 66 high schools in 23 towns (Fig. 1). Results of the individual schools are presented in Supplemental Table S1. Out of this sample, 1803 males and 782 females were incorporated into this study, because they listed a place of residence in the targeted eight counties   (Table 3).
Male height. The average height of 1803 males residing in the eight examined counties was 182.7±6.7 cm. This mean did not change much, when only boys aged ≥18 years were considered (182.6±6.7 cm, n=1558), or when it was corrected for population size in these eight counties (182.6 cm) (Supplemental Table S2). After this correction, the average height is 182.8 cm in the seven counties of Adriatic Croatia and 183.7 cm in the four counties of Dalmatia proper. Regional differences were large (3.5 cm), from 180.6 cm in the county of Karlovac to 184.1 cm in the county of Split-Dalmacija (Table 1). All samples have a normal distribution of values (Table 2).    Remarkably, the anomaly in the area of Čapljina (185.9 cm) and Široki Brijeg (185.4 cm), where we found the tallest means in BiH, has an analogy on the Croatian side of the border in the towns of Metković (184.9 cm), Imotski (186.2 cm) and Makarska (187.6 cm) (Table 3).
Although all the samples are relatively small (21-38 males), such a high frequency of extremely tall means within a small geographical area cannot be a mere coincidence. This suggests that the peak of male height should be sought in the area demarcated by Makarska - County ( Table 3 Average male and female height in 14 individual towns accoding to the selfreported place of residence. Only towns with at least 20 measured individuals are included. In the direction to the north of this area, height begins to decrease quite rapidly, although this change is not always evident at the level of individual towns. which is approx. 25 km further inland, were much shorter (182.8 cm, n=39) and a sample of boys resident in Knin reached only 181.7 cm. We cannot exclude the possibility that these large differences between coastal and inland regions are due to relatively small sample sizes, but the same findings were previously reported even by Prebeg (1988) and ascribed to economic factors.
Height further drops by 0.6 cm in the county of Zadar (182.8 cm) and this drop again appears to be more pronounced inland, as indicated by the school of Gračac (178.8 cm, n=13). Still, it should be mentioned that the area of Gračac is very sparsely populated and it is very difficult to collect samples, which would be adequately representative. In addition, the local population consists of many Croatian immigrants from BiH, who may not have the same genetic background.
In the county of Lika-Senj, the decrease of height is relatively the most dramatic (  In general, it seems that girls in counties with the tallest boys (around 184 cm) reach a height of approximately 169 cm (Table 4). This is a very tall mean, but not as tall as in the young women aged 20-21 years in the Netherlands (170.5 cm) (Schönbeck et al., 2012) and shorter than the results of Pineau et al. (2005) (Steckel, 1996). found that in our unpublished sample of 141 countries/territories, from which male and female data on height are available, the mean sex difference ranges between 11-12 cm in short-statured nations to 13-14 cm in tall-statured nations, with a global mean of 12.4 cm. The gap is only 13.1 cm even in the world's tallest nationthe Dutch. Therefore, the sex differences between men and women in former Yugoslavia appear to be larger than the global trend line predicts (Fig. 3).

Average height (males) Eight counties of the Adriatic coast Seven countries/territories of the former Yugoslavia
relative arm span (100.6-101.6%). The differences in relative sitting height are not significant between the two Croatian regions (p=0.14), but those in relative arm span are (p<0.001). relative arm span (99.9±2.2%) significantly differed from boys residing in the same counties (p<0.001) and pointed to much shorter limb length relative to stature. The fact that women have relatively shorter limb length than men is well documented (Eveleth & Tanner, 1976).
Socioeconomic factors. Similar to our previous study in BiH, we collected information on the education of parents. These self-reported data were available in 1708 boys and 634 girls.
In contrast with the results in BiH, where sons of university educated parents were 1.9 cm taller than sons of parents without university education, in the present study we found a much smaller disparity in this regard (0.5 cm: 183.1 cm vs. 182.6 cm), which was not significantly different (p=0.28). The smaller magnitude of this difference was also indicated by the fact that elite high schools (gimnazija) were not as often among the tallest schools as in BiH. The results were somewhat more pronounced in girls (1.1 cm: 168.1 cm vs. 167.0 cm), although they did not reach significance either (p=0.18). At the same time, the percentages of boys and girls in each category of parents' education were very similar, which suggests that these selfreported data can be regarded as very trustworthy (Table 7).  Zagreb and the counties of Istra and Varaždin). In addition, the neighbouring county of Istra has the fourth highest netto salary in Croatia. Therefore, we can assume that height in these two counties is disproportionately elevated due to favorable economic conditions.

Males
In contrast, the mountainous county of Lika-Senj has the lowest netto salaries among the eight examined counties. However, even this county is still ranked 11 th out of 21 Croatian counties.
In other words, eight out of top 11 Croatian counties with the highest netto salaries belong to the Adriatic region that we examined in the present study. This must undoubtedly be attributed to the effect of tourism. Therefore, the impact of economic factors could potentially manifest if we compared counties of the Adriatic region with the rest of Croatia. Similar to Prebeg (1988), we can also suppose that the shorter statures documented in the inland of Dalmatia are due to the fact that the economic benefits of tourism are limited to the Adriatic coast.
Nutrition. The Croatian Bureau of Statistics was not able to provide any data on the regional food production or consumption, and hence our nutritional analysis depends only on crude national statistics of food supply from the FAOSTAT database. These data show that protein consumption in Croatia has dramatically increased since 1992 and most of this increase can be attributed to animal proteins (Fig. 4). The consumption of key proteins from dairy and pork in 2013 is almost twice as high as 1993.
However, this development apparently copies the trend of the GDP per capita, which  indeed do carry single nucleotide polymorphisms (SNPs) associated with tall stature (Robinson et al., 2015).

DISCUSSION
To our knowledge, this study constitutes the most detailed report on the regional differences in stature on the Adriatic coast of Croatia since the 1980s. As already mentioned above, these differences reached 5 cm (166-171 cm) at the end of the 19 th century and this range has largely persisted until today, because we documented a 3 cm gap (181.1-184.1 cm) between the counties of Istra and Split-Dalmacija. It is intriguing that height in individual counties mirrors the height in the neighbouring cantons of BiH. Therefore, if any local factors influence stature, they must work similarly on both sides of the border.  (Schönbeck et al., 2012), it should be noted that the average is only 182.4 cm and 169.7 cm in the age category of 18 years, and 183.6 cm and 170.1 cm in the age category of 19 years. The size of the samples is also quite small (only 211 males and 215 females aged 20-21 years) and it is not entirely clear, if the samples past high-school age (18+ years) are not artificially elevated due to the inclusion of university students (as mentioned in the 'Methods' section of that paper). Therefore, these data from the Netherlands cannot be perfectly compared with our data from the Balkans, where we targeted males and females aged 17-20 years, with a preponderance of 18-year olds. In fact, both 18-year old boys from Dalmatia (n=839) and Herzegovina (n=632) reach 183.6 cm, and Dalmatians would be even slightly taller than Herzegovinians, if we took population size in regions into account. Although the mean height of Montenegrin boys aged 17-20 years is only 182.9 cm, when corrected for regional population size, they may also be taller than their Dutch peers. Figure 7 shows that the area with tall statures above 181 cm roughly copies the outer mountain ridge of the Dinaric Alps. Only the region of Bijeljina in northeastern Bosnia is an exception, possibly due to good economic conditions. Areas with the tallest statures above 182 cm lie on the inner side of the ridge in Herzegovina, Dalmatia and central/northwestern Montenegro. This picture shows that height in the Dinaric Alps is not connected with the limestone bedrock per se, which would not support the hypothesis of Coon (1970), who speculated that height in North Albanians living on limestone is elevated due to the high mineral content in the food chain. Rather, height peaks behind the mountain range, which historically served as a barrier to genetic flow. Interestingly, the height of contemporary Albanian men is only 174.0 cm, which is 8.9 cm shorter than in Montenegrins, and 5.5 cm shorter than in Kosovar Albanians. Preliminary results from Albanian universities confirm that these large differences are real (S. Popović, 2017pers. communication). Because the quality of nutrition in Albania appears to be similar to that of BiH, Croatia, or Serbia, and the GDP per capita in Kosovo (for 2016) is 18% lower than in Albania (The World Bank), this remarkable phenomenon deserves further research.
It is striking that we cannot again confirm the results by Pineau et al. (2005)   As already mentioned (Grasgruber et al., 2017), Pineau et al. collected at least some of their data in Herzegovina and Dalmatia via personal communication with the local physical education teachers, which could influence their results. Furthermore, the secular trend of youths in Tuzla schools was not negatively affected by the Bosnian war (1992)(1993)(1994)(1995) and continued at a relatively fast rate (Grasgruber et al., 2017;Hadžihalilović et al., 2006), so we do not suppose that height in other regions of BiH would decrease, especially considering the fact that boys measured during our survey in BiH were growing up after the end of the war.
Nevertheless, recent evidence shows that height in some Croatian regions may have really decreased during the last two decades.

Older birth cohorts developed normally. In Zagreb, the research of the Andrija Štampar
School of Health between 1951-1991 documented a continuous, positive height trend (Fig. 8) (Prebeg et al., 1995). However, studies of the Institute for Anthropological Research between 1991-2010 showed a significant decrease from 180.7 cm to 180.1 cm in boys and from 167.1 cm to 165.2 cm in girls (Petranović et al., 2014). Although these two institutions apparently targeted different types of schools and the latter surveys were less representative, it is clear that no increase of height has occurred in Zagreb since 1991. This development can be connected with the dramatic decline of the economy in the early 1990s, which recovered as late as during the 2000s. Based on the studies of the Andrija Štampar School of Health (Jovanović et al., 2003) and the Institute for Anthropological Research (Petranović et al., 2014). Still, the mean height of 18-year olds in Croatia has increased by 2.9 cm in boys and 1.8 cm in girls between 1980-84 and 2006-08 (Jureša et al., 2012). Historical data show that between 1883-2008 (125 years), the average Croat male has grown by 15 cm (from 165.5 cm to 180.5 cm), which means an average rate of 1.2 cm/decade. Based on the information listed by Coon (1939), we can estimate that the height gain of young men in the county of Istra has been approximately 15 cm as well. According to the records of Austrian-Hungarian recruits around the year 1870 (Komlos, 2007), young men from the town of Zadar (Zara) were the tallest in the whole empire at 168.7 cm, which is a difference of +14.1 cm, when compared to the present study (1.0 cm/decade). However, it should be noted that these historical data do not necessarily represent the same populations, due to migrations to the coastal regions occurring in the course of the 20 th century.
Historical information from other regions of the Adriatic area is scarcer. As already mentioned, the most recent nationwide survey comparable with the dimension of our work was conducted in 1980-1984 (Prebeg, 1988). Another nationwide survey was performed in 1991-1993, but was limited to a mere four areas (Prebeg, 1998). Very few detailed numbers from these studies were published, but some rough data on Split are available (Jovanović et al., 2003). They show that in 1980-1984, the mean height of 18-year olds in Split was 181 cm in boys and 167 cm in girls. In 1992, it reached 182.5 cm and 170 cm, respectively. Although the height of girls from the latter survey appears unlikely high, these values show that at least in boys, the secular trend was continuing even during the subsequent economic depression.
This could explain why the nationwide average increased as well, despite possible stagnation or decline in Zagreb and other areas of mainland Croatia. Still, our present study indicates that these economic disturbances may have eventually affected even Dalmatia since 2001-2003.

CONCLUSION
In summary, the data presented in our article demonstrate that people from Dalmatia currently belong to the tallest in the world, and local young men are even the tallest in the age category of 18 years. However, this phenomenon is limited only to the territory of Dalmatia, Herzegovina and Montenegro. Other regions of Croatia are characterized by a much shorter stature and these large regional differences have persisted at least since the end of the 19 th century. The taller statures in Adriatic Croatia can be, at least partly, linked with more favourable economic conditions, but these factors cannot explain, why the north-to-south gradient is very similar both in Adriatic Croatia and in BiH, on both sides of the mountain range forming a natural border between these two countries. Because we are not aware of any environmental factor that could be responsible for these geographical trends, specific genetic predispositions shared by these populations are the most likely explanation. On the other hand, the striking shortness of Albanians, when compared to the neighbouring Montenegrins and Kosovar Albanians, represents a different kind of extreme, which would require clarification in future studies. Another fundamental finding is the fact that the secular height trend in Croatia has been negatively influenced by the economic depression in the 1990s. The onset of the economic crisis in 2008 further delayed a marked improvement in living standards. However, because the quality of nutrition in Croatia is still below the European standards, a further continuation of the positive height trend is still possible. In the near future, we would want to cover even the rest of mainland Croatia and describe regional differences across the whole country.