A comparison between the secular trends of stature and of some socio-economic factors in Italy

L. Ulizzi Istituto di Genetica, Universit~z di Roma and Centro di Genetica Evoluzionistica, C.N.R., Roma, Italy

A Comparison Between the Secular Trends of Stature and of some Socio-economic Factors in Italy

Secular changes of stature of adult Italian males were compared with trends of some relevant health and socio-economic variables: survivorship up to 19 years of age, protein intake, average income and illiterL. Terrenato acy. The results indicate that during the pre-World War II period Cattedra di Genetica Umana, the relationships between each of these variables and stature were different from those of the post-war period. Universitg~ di Sassari, Italy Also the effects on stature distribution appear to be different in these two periods : in the first one the curve tends to become normally shaped Received 13 October 1982 and while in the second the mean value is increasing at a higher rate than 30 October 1982 before. In very recent years no significant modification was detected. These findings are discussed in terms of the possible full expression of Keywords: stature (factors affecting), stature (secular trend) the genetic endowment for stature achieved in the e~lvironmental conditions typical of a contemporary industrialized country.

1. I n t r o d u c t i o n T h e occurrence of a secular increase in height has been d o c u m e n t e d in most industrialized countries; in some cases a slowing down or even a stopping of this positive trend has b e e n recently observed in at least m i d d l e a n d u p p e r socio-economic classes ( T a n n e r , 1978; C a m e r o n , 1979). I n a previous p a p e r ( T e r r e n a t o & Ulizzi, in press) a study performed on I t a l i a n conscripts b o r n from 1874 to 1960 showed that the m e a n stature increased in this period by 9 c m (i.e. a b o u t 1 cm/decade). T h e analysis of the different I t a l i a n regions, which present at one time very different living conditions, m a d e it possible to study the characteristics of the observed secular t r e n d in very different socio-economic environments. T h e interregional comparison has i n fact shown different rates a n d t i m i n g of the t r e n d ; i n particular, in the n o r t h e r n regions (where the industrialization process started earlier a n d is at present at a more a d v a n c e d level t h a n in other parts of Italy) the secular trend of stature started earlier a n d seems now to have a p p r o a c h e d a plateau. I n the southern regions, on the other hand, w h i c h u n t i l now present a relatively poorer level of living conditions, the trend is still positive although at a lower rate t h a n in the past. It is widely accepted that the secular trend is associated with an increasing expression of the genetic capacities for stature, since the e n v i r o n m e n t a l factors affecting h u m a n growth are getting more favorable. U n f o r t u n a t e l y , a direct analysis of the causal relationships b e t w e e n the secular t r e n d of stature a n d factors likely to affect this character is only seldom feasible. Moreover, the correlation coefficients between stature a n d socio-economic conditions, even if widely used, did not result suitable to establish a causal relationship a n d merely suggest that d u r i n g the same period of time, stature a n d socio-economic factors are c h a n g i n g with more or less similar patterns. Therefore, a comparative analysis of the graphical representation of the secular trend of stature a n d that of relevant socio-economic variables could be more informative. I n the present p a p e r there are e x a m i n e d d u r i n g the last century, i.e. d u r i n g a period in which Journal of Human Evolution (1982) 11, 715-720 0047-2484/82/070715 -- 06 $03.00/0

(~) 1982 Academic Press Inc. (London) Limited

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L. U L I Z Z I A N D L. T E R R E N A T O

Italy experienced dramatic changes in living conditions, the patterns of stature and socioeconomic indicators, such as survivorship up to 19 years of age (which for the purposes of this study can be considered as an indicator of the general health status of the population), protein intake, average income per capita and percentage of illiteracy. For average income the analysis was performed at regional level also, in order to compare its secular trend in different environmental conditions. 2. M a t e r i a l s a n d M e t h o d s

Original data concerning the stature of all Italian conscripts born from 1874 to 1960 were obtained from Military Records. Survivorship up to 19 years of age (i.e. the mean age of examination of conscripts) was drawn from Generation Tables (1790-1964) by Natale & Bernassola (1973), from which v a l u e s u p t o 1945 generation were used. For subsequent years the Tables forContemporaries by Golini et al. (1977) were used. Protein, fat and carbohydrates intake values and illiteracy percentages were obtained from Istituto Centrale di Statistica (ISTAT) reports (1965, 1976). Average income was calculated using I S T A T national data (1976) and regional economic levels given by Tagliacarne (1963). The figures reported here are expressed as 1938 purchasing-power Italian lire. Within the period examined some specific years, which turned out to be particularly informative on the basis of a preliminary analysis, were chosen both for stature and average income. For protein intake, the averages of ten-year intervals around the selected years were used. T h e World-war periods were excluded because they might express specific phenomena that are beyond the purposes of the present study. Standard statistical methods related to the characteristics of the normal distribution were used. 3. R e s u l t s a n d D i s c u s s i o n

In Figure 1 the secular increase of stature is plotted against survivorship up to 19 years of age, average income and protein intake. For survivorship, the trend is linearly increasing for people born from 1874 to 1951 ; since then the increase of stature proceeds at a higher rate as compared with that of survivorship. An approximate reflection of this pattern is shown both by protein intake and average income. In fact, in the 1950s the increase of both these variables largely exceeds that of stature in comparison with the previous period. T h e analysis of the three patterns suggests that the period of almost a century can be subdivided in two intervals, the first lasting from 1874 to 1951, the second from 1951 to 1960. In these two periods the Italian population lived in very different environmental conditions. Following World War II, Italy has experienced a drastic improvement in socio-cultural, economic and hygenic conditions, as all the indicators used here show. For the survivorship up to 19 years of age, it appears that in the first period a very high increment (from about 50% to about 90%) is associated with a stature gain of about 6.4 cm, while during the second period a relatively low increase of survivorship (from about 90% to about 93 %) is associated with a stature gain of 2"6 cm. These figures therefore suggest that the relationship between stature increase and reduction in mortality is different in the two periods, although it is worth noting that the small change in survivor-

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STATURE AND SOCIO-ECONOMICFACTORS Figure 1. Secular trend of stature plotted against survivorship up to 19 years of age, animal protein intake in grams per capita per day and average income per capita per year expressed as 1938 purchasing-power Italian lira.

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ship achieved in the post-World War II period might reflect an improvement of general health conditions higher than ever before. As to the relationship of stature v s protein intake, during the first period at a stature net gain of 6-4 cm it corresponds a protein intake increase of about 10 g, while in the second period at a similar net gain of protein intake it corresponds a stature increase of 2.6 cm. A similar pattern is found when the average income per capita per year is considered. During the first period the stature gain of 6.4 cm is associated with an increase of about 1700 Italian life, while in the second period an even greater increase of income (about 2200 Italian life) is associated with a stature increase of 2-6 cm. It is interesting to note that during the period examined, protein intake and average income are highly correlated, suggesting that whenever economically feasible, the diet improves. O u t of the dietary components, animal-protein intake turned out to be the most increased in the last century and for this reason it has beerl chosen as an indicator of the nutritional status of the population. Namely, the increase of animal-protein intake per capita per day is about 140%, while in the same period protein of vegetable origin decreases by about 30%. Animal and vegetable fats increase by about 50% and 30% respectively. For carbohydrates, those of animal origin increase b y about 130%, while for those of vegetable origin no significant variation is found. O n the whole, calories increase by about 10 %, the percentage of those of animal origin passing from about 10 % to about 20%. Among the available regional trends ofthesc three variables, the average income turned out to be the most informative.

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L. ULIZZI AND L. TERRENATO Figure 2. Secular trend of stature plotted against average income in Italy (dotted line) and in six selected Italian regions: 1. AbruzzoMolise; 2. Calabria; 3. Basilicata; 4. Lombardy; 5. Ligury; 6. Latium. 1.75

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F i g u r e 2 shows the results graphically. I t can be seen t h a t for three southern regions (Abruzzo-Molise, C a l a b r i a a n d Basilicata) which are r e p r e s e n t a t i v e of the less well-off a r e a of I t a l y , a threefold increase of i n c o m e (starting from v e r y low levels) is associated with a v e r y high rate of stature increase. O n the other h a n d , n o r t h e r n regions a n d central ones ( L o m b a r d y , L i g u r y a n d L a t i u m ) , which are r e p r e s e n t a t i v e of the well-off p a r t of Italy, show t h a t over a tenfold increase of i n c o m e (but s t a r t i n g from higher levels) is associated w i t h a relatively low r a t e of stature increase. T h e r a p i d secular changes of the different I t a l i a n regions c a n be a p p r e c i a t e d also in F i g u r e 3, w h e r e the regional t r e n d for illiteracy is reported. D u r i n g the last c e n t u r y the n o r t h - s o u t h g r a d i e n t is highly a t t e n u a t e d even if small differences are still present in 1961. Figure 3. Illiteracy percentages of the Italian regions in selected years. (///): Northern; (:::): Central; (VI): Southern; ( i ) : Sicily and Sardinia Islands.

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FACTORS

A m o n g those examined it is perhaps useful to identify two kinds of socio-economic variables, both on tile basis of their numerical structure and of their behavior in association with stature increase. O n one hand, percentage estimates, like mortality and illiteracy, are regularly decreasing with time and nearly reach absolute minimal value; in these cases, all the regions tend to a p p r o a c h the same low level and therefore regional heterogeneity tends to disappear; also their direct and/or indirect effects on stature must accordingly reach a minimal value. O n the other hand, absolute measurements like income and protein intake are continuously increasing with time and different regions still continue to show a high degree of heterogeneity; in this case also, however, their effects on stature appear to become less evident. These two kinds of p h e n o m e n a are clearly reflected in the three trends depicted in Figure I. I n conclusion, from m a n y points of view, Italian regions are still heterogeneous, but the question to be answered is w h e t h e r they have reached the socio-economic level necessary for a complete expression of stature genotype. I n fact, beyond this level (a threshold value as far as stature is concerned) any further variability should become irrelevant for h u m a n growth. For protein intake, it is very suggestive that the standard requirement r e c o m m e n d e d by F A O / W H O (1973) for a normal growth was attained in Italy only in the late 1950s. Figure 4. Changes of stature distribution characteristics: mean values plotted against skewness and kurtosis. For the two considered periods the mean increases are also reported.

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A n indirect answer to the same questiott is to be found in the secular changes of stature distribution characteristics. T h e y also are of two kinds: the modification of the shape of stature distribution and its shifting towards higher values. As it appears in Figure 4, the two effects can be independently examined subdividing the considered period in two parts. I n the first part (up to 1938) the skewness and kurtosis rapidly reach values typical

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of a normal distribution, while the mean stature increase is relatively low (about 0.07 cm/ year). After 1938 the stature distribution keeps on becoming normally shaped and very rapidly shifting to the right (0"2 cm/year). In the very recent years the secular increase is approaching a plateau and m a n y regions (the well-offones) appear to reach a steady state. Therefore, one can hypothesize that during the first period the most relevant effect was the progressive elimination of the pressure acting on the shape of the distribution. During the second period the improvement in socio-economic conditions affected the whole distribution, determining its shifting to the right. This phenomenon is now approaching its final phase and no further modifications either of shape or position of the distribution are to be expected. References

Cameron, N. (1979). The growth of London schoolchildren 1904-1966: an analysis of secular trend and intra-eounty variation. Annals o f Human Biology, 6, 505-525. F A O / W H O (1973). Energy and Protein Requirements, Report of a Joint FA O / WHO Ad Hoc Expert Committee, FAO Nutr. Meet. Rep. Ser. No. 52, R o m a ; W H O Techn. Rep. Set. No. 522, Gen6ve. Golini, A., Soliani, L., Giavelli, G. & Zanni, R. (1977). Tavole di mortaliM ridotteper le regioni e le ripartizioni italiane. 1951-1961-1971. Istituto di Demografia dell'UniversitY, Roma. Istituto Centrale di Statistiea, Roma (1965). Annali di Statistica, Serie VIII, Vol. 17. Sviluppo della Popolazione Italiana. Istituto Centrale di Statistica, Roma (1976). Sommario di Statistiehe Storiche deU'Italia. 1861-1975. Natale, M. & Bernassola, A. (1973). La mortalitd per causa helle regioni italiane. Istituto di Demografia dell'UniversitY, Roma. Tagliaearne, G. (1963). Lo sviluppo economico delle regioni italiane in tre quarti di secolo (1885-1961). Scritti di eeonomia e statistica in memoria di Alessandro Molinari. Milano. Tanner, J. M. (1978). The interaction of heredity and environment in the control of the growth. Fetus into Man. Harvard University Press. Terrenato, L. & Ulizzi, L. (1983). Genotype-environment relationships: An analysis of stature distribution curves during the last century in Italy. Annals of Human Biology (in press).