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THE INFLUENCE OF ENVIRONMENTAL FACTORS ON PHYSICAL '% "' >.• 

GROWTH IN SCHOOL AGE: A STUDY OF LOW LEVEL LEAD fpTljfl?, •), ft ^ .!'" 

EXPOSURE UJ] **—^ 

v < 

T. Lyngbye^'2 , o.N. Hansen3, P. Grandjean* 

1 Departmen t of Environmenta l Medicine , Odens e 

University, Odense, Denmark. 

2 Institute of Psychiatric Demography, Psychiatric 

Hospital, Aarhus, Denmark. 

3 Institute of psychology, University of Aarhus, 

Aarhus, Denmark. 

Introduction 

Environmental factors have long been suspected to play 

a role for the physical growth. This assumption is based on 

indirect evidence such as the secular trend of increasing 

height (1), differences of height within the same 

population and the influence of social class on the growth 

(2). The influence of specific environmental factors such 

as lead absorption or mothers smoking during pregnancy have 

been examined in large scale crossectional studies (3) and 

in longitudinal studies(2). The current Aarhus study, 

designed to identify undue effects of early lead exposure, 

also evaluate the impact of social, behavioral, nutritional 

and medical factors as well as tobacco smoking during 

pregnancy. 

Material and methods 

A cohort study with a nested case-control group was 

performed in the Aarhus municipality among children joining 

the first grade in 1982-83. Collaboration was obtained with 

schools covering 82.5% of the population in all 2.412 

children, who were asked to donate natural shed deciduous 

teeth through the form master. At least one tooth was 

recieved from 1302 children (54%), who were representative 

for the total cohort (4). The teeth were analyzed for their 
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lead concentration in the circumpulpal dentin (5,6). 

Children with a concentration above 18.7 ug/g were selected 

for the case group and matched for gender and socioeconomic 

status to an equivalent number of children with dentin 

concentrations below 5.0 ug/g serving as control group (6). 

Two-hundred families were visited by the pediatrician of 

the team in their homes and interviewed on the childs 

medical history, dietary history, behavior, tobacco smoking 

of the parents and sociodemographic factors. Based on the 

interview children were excluded from further comparision, 

if unsuited on account of medical risk factors for impared 

growth and developement. Twenty nine children were excluded 

for medical reasons (unpublished data) and 14 did not want 

to participate further (4). Four were excluded because of 

foreign etnic background. 

Two years after the interview a consent was obtained 

by letter, for information on growth and health factors 

from the school phycician, from 145 children (72 cases and 

73 controls). These children were meassured (height and 

weight) on 3 to 4 occasions between the ages of 6 and 10 

years. These meassurements were plotted on growth curve 

charts standardized in a Danish population (1). The growth 

of each child could thus be expressed as a percentile for 

length, and weight for height, normalised for age and 

gender. 

Statistical analysis 

selected variables were analyzed in related groups and 

taken into individual multiple stepwise analyses. The 

variables explaining variance at a p-level of 0.1 or less 

were taken into a final stepwise regression and lead group 

was added to this model. 
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363 

Results 

lengcn. m e only social tactor tnat snowea association wicn 

length was the mothes age at the birth of the proband, 

standardized for parity. This variable behaved like the 

medical variables and was thus further considered within 

this group. 

Among the the nonmedical factors (individual 

analysis), "small appetite" and tobacco smoking during 

pregnancy were significant explanators (p = 0.01 and p= 

0.02) of 7 % of the variance. Among the medical factors 

(individual analysis) cesarean sect ion / young age of the 

mother and previous abortions were all significant at a plevel below 0.03 and explained 17 % of the variance. When 

~« -'i-'1 ;-i~.~- medical variables and lead-group 

Discussion 

It is known fron other studies that protein intake is 

related to growth (3). This equivalates to the variable 

"small appetite" in this study. The variable lost its 

explanatory power in the final weighting, and problaly 

could the seemingly assosiation be considered a consequense 

of, rather than a cause for retarded growth in the present 

population. 

The variable cesarean section is an indicator of the 

medical factors that lead to the artificial delivery. This 

is in most cases an indirect evidence for placenta 

incufficiency. 

Mothers' tobacco smoking during pregnancy has in a 

longitudinal study exhibited a dose-response pattern as 

predictor for height at 7 years (2). The present study 

replicate tobacco as a predictor for height while taking 

more medical and environmental factors into account. 

The lead effect in the study is found in a child 

population with a very homogeneous social background and 

with no ethnic minorities. The notion that the association 

is the expression of a biological effect is supported by 
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t h e findin g of lead-grou p a s a riskfacto r fo r learnin g 

disabilitie s in th e same cohort (unpublishe d data ) and of 

impare d performanc e by psychologica l testin g (7) . The 

averag e bloo d lea d i n th e cohor t wa s belo w 6 0 ug/ 1 

wholebloo d (unpublishe d data) , so i t seems tha t even in 

such a low-leve l lead-pollute d area , earl y lead-absorptio n 

is a riskfacto r for impared length-growt h in schoolage . 

References 

(1) Andersen, E. , Andersen, H. , Hutchins, B. , Nyholm, M., 

Peitersen , B. Rosen, J. , Tamdrup, E. & Wichmann, R. Heights 

a n d weight s i n Danis h schoo l childre n i n 1971-1972 . 

Ugeskrift fo r lager , 136; 2796-2802 (1974). 

(2) Davie , D. , Butler, N. & Goldstein , H. From Birt h t o 

Seven.Th e Second Report of th e Nationa l Chil d Development 

Study (1958 Cohort).London , Longman, 1907, pp 8 1-86. 

(3) Schwartz , J. , Angle , C. , & Pitcher , 

Betwee n Childhoo d Bloo d Lea d Level s 

Pediatrics , 77 : 281-288 (1986). 

H. Relationshi p 

a n d Stature . 

(4) Lyngbye , T. , Hansen , O.N. & Grandjean , P. Bia s 

resultin g from non-participario n i n childhoo d epidemiologi c 

stuidies : A stud y of low-leve l lea d exposure . Scandinavia n 

Journa l of Socia l Medicine , in press (1987). 

(5) Grandjean , P. , Hansen, O.N. & Lyngbye, K. Analysis of 

lea d in circumpulpa l denti n of deciduou s teeth . Annals of 

Clinica l and Laborator y Science , L4:270-275 (1984). 

(6) Grandjean , P. , Lyngbye , T. & Hansen , O.N. Lead 

concentratio n relate d t o toothtyp e an d analytica l 

technique . Journa l of Toxicolog y and Environmenta l Health , 

2 0 : 437-445 (1986). 

(7) Hansen, O.N., Trillingsgaard , A., Beese , I. , Lyngbye, 

T. & Grandjean , P. Neurobehaviora l methods in assessmen t of 

childre n wit h low-leve l lead-exposure . Neurobehaviora l 

Method s i n Occupation. a 1 an d Environmenta l Health , 

Copenhagen, WHO, Regiona l Offic e fo r Europe , 1985: 183-188 .