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Original Article


Al-Hashem, Fahaid H. MBBS, Phd (UK)

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Journal of Family and Community Medicine: Jan–Apr 2006 - Volume 13 - Issue 1 - p 35-40
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Certain biochemical, physiological and micro-anatomical responses occur during acclimatization and adaptation to chronic hypoxia of high altitude.1 Among these responses are changes in haemoglobin levels.2 Several studies have been carried out in different high altitude populations throughout the world.36 However, no study has dealt specifically with the Southwestern highlands of the Kingdom of Saudi Arabia where both environmental factors and population genotypes differ widely from other studied areas.

The topography of the Asir Region in the Southwestern part of the Kingdom of Saudi Arabia varies from an altitude of 3150 m to sea level.7 The region is, therefore, ideally situated to provide information on possible effects of altitude on haemoglobin levels. However, no carefully controlled study in children specific to this region has been reported. The present study was, therefore, undertaken to determine the levels of haemoglobin and some of its correlates in high and lowland children of the Southwestern region of the Kingdom of Saudi Arabia.


The study was carried out at high and low altitude areas of the Asir region in the Southwestern part of the Kingdom of Saudi Arabia. Alsoda and the villages around Sabit Allia city were selected to represent the high altitude areas (2800-3150 m above sea level) while the villages around Mohyel city, situated at 500 m above sea level, represented low altitude areas. Environmental data on these areas are shown on Table 1.7 Alsoda lies about 600 km south of Jeddah (the second largest city in the kingdom) and Sabit Allia is about 560 km south of Jeddah. Mohyel is in Tihama valley about 520 km south of Jeddah. The areas involved in the study had ready access to health facilities and enjoy an adequate diet comprising mainly of meat, chicken and rice. Potable water and electricity are also available in the two areas.

Table 1:
Environmental data on the high and lowland of the study

Data were collected from 1331 children aged 1-15 years who were born and permanently resided at a high altitude and 1185 children of comparable age born and permanent residents at low altitude. The children were selected from different age groups from different households. These numbers constituted about 90% of children registered in the health centers at high and low altitude. Each child was first subjected to a detailed clinical examination. Children in whom pathological conditions were detected by clinical examination as well as children with positive stool examination for pathogenic parasites were excluded from this study. All children sampled were Arabs and of Saudi nationality. All measurements were made at the health centers. This study was carried out in the period between 1998 and 2000.

For each child, age was calculated and recorded from birth certificates at the time of examination. For children under two years, the body weight was measured on a baby scale and the supine height was taken with a measuring board (Harpenden), and for children over two years the body weight was measured with an Avery beam weighing scale and the standing height was measured with a stadiometer (SECA). The weights of the children in minimal clothing were measured to the nearest 0.1kg and the heights and supine lengths were taken without shoes to the nearest 0.5cm.Venous blood samples were taken into heparinzed tubes to determine haemoglobin using cyanmethaemo-globin method.8 The basis of this method is to dilute blood in a Darbkin's reagent which consists of potassium cyanide, potassium ferricyanide and sodium bicarbonate. Haemoglobin, methaemo-globin and carboxyhaemoglobin are all converted into cyanmethaemoglobin. A medium standard is provided and labeled with the concentration of haemoglobin. The absorbance of the cyanmethaemoglobin solution and the medium standard are then measured in a photoelectric colorimeter at a wavelength of 540 nm (to give maximum absorbance). The haemoglobin concentration is then computed as follows: Haemoglobin (gm/dl) = (absorbance of the test / absorbance of the standard) × concentration of the standard

To determine the effect of age on haemoglobin levels, the children were divided into different age groups. Table 2 shows the number in each age group by sex.

Table 2:
The number of children in each age group by sex

At different stages of the study, the collected data were compiled and fed into an IBM computer. SPSS package version 10 was used for standard statistical analysis including multiple regression. Student's T-test was used to determine statistical significance. P<0.05 was considered statistically significant.


Table 3 shows the mean ages and some of the characteristics of high and lowland children by sex. The study was confined to children from 1 to 15 years. Compared with lowland children, highland children were found to be significantly heavier and taller. This was true for both boys and girls. When the two sexes at the same altitude were compared, boys were found to be significantly lighter and shorter than their respective girls (p<0.001 and < 0.01 respectively).

Table 3:
Mean values ± standard deviations of age, weight and height

The mean haemoglobin levels in high and lowland children by sex are shown in Table 4. The mean haemoglobin levels were significantly higher in highland children than their counterparts living in the lowland areas. This was true for both boys and girls (p<0.0001). At both altitudes, there were no significant differences in the mean haemoglobin levels between boys and girls.

Table 4:
Mean ± standard deviations of hemoglobin (Hb) levels of Saudi high and lowland children by sex

Figure 1 shows the relationship between haemoglobin levels and age of children living at high altitudes and those at low altitudes. The haemoglobin level in lowland children increased steadily with an increase in age, from 9.9 g/dl in the youngest group to 12.1 g/dl in the oldest and from 9.6 g/dl in the youngest group to 11.8 g/dl in the age group 11-13 in boys and girls respectively. Similar trends were seen in highland children except that the level of increase was very slight. In highland boys the haemoglobin increased from 12.9 g/dl in the youngest group to 13.8 g/dl in the oldest group, and in highland girls the increase was from 12.9 g/dl in the youngest to 13.5 g/dl in the 9-11year-olds, after which there was no increase with increasing age. In all age groups, there were no significant differences in haemoglobin levels between boys and girls at each study site except in the age group 13-15 years where lowland boys tended to have significantly higher haemoglobin levels than their girl counterparts (p< 0.0005).

Figure 1:
Relationship between mean hemoglobin levels and age in high and lowlands boys and girls

Multiple regression analysis was done to assess the impact of weight and height on haemoglobin levels in the children. This was done separately for boys and girls. Table 5 indicates that the multiple linear regression models (haemoglobin as a function of weight and height) were statistically valid and that the linear fits were adequate. The multiple regression equations that describe the data more efficiently are: Haemoglobin =10.1+ (6.03 × weight) + (0.01 × height) for boys and Haemoglobin= 10 + (0.02 × weight) + (0.01 × height) for girls.

Table 5:
The multiple linear regression models (hemoglobin as a function of weight and height) of Saudi high and lowland children by sex

In both boys and girls at high and low altitudes, the regression coefficients indicated that weight and height were significant contributors to haemoglobin levels (for boys p<0.003 and for girls p<0.005 for both weight and height).


The results presented in this paper have shown that highland children of the Southwestern heights of the Kingdom of Saudi Arabia have significantly higher haemoglobin levels than their counterparts of comparable age living in the lowlands. In addition to altitude interpopulation, differences in haemoglobin levels are sometimes partly due to racial or dietary factors910 or due to adaptive evolutionary changes.11 In this study, the racial and dietary factors were eliminated by using low altitude children of the same ethnic background and the same dietary habits as control. Thus, the factor that appears to be at work in this situation is environmental. High altitude hypoxia is known to cause an increase in erythropoietin level which in turn increases red cell mass and hence haemoglobin levels.12 In addition, and because of the tropical nature of the studied area, the lowland children experience continuous high temperatures and therefore have a higher incidence of tropical infections, namely, leishmaniasis13 and malaria14 which are known to cause a fall in haemoglobin levels.1516 On the other hand, highland children are exposed to cold weather which tends to reduce tropical infections. It is most likely, therefore, that the differences in haemoglobin levels between high and lowland children were related to the combined effects of high altitude hypoxia and the beneficial effects of the prevailing milder environmental conditions on the health of children at high altitude.

The mean levels of haemoglobin obtained in this study for highland children were not much different from those obtained by Khan et al17 from Abha city which lies in the same area of study (13.8 g/dl) although the sample in that study included both Saudi and non Saudi children who were not permanent residents of the area of study. For lowland children the levels obtained were lower than what had been reported by Ghafouri et al18 from Jeddah which lies at sea level (13 g/dl). However their results were obtained from an urban area and did not include children from 1-5 years.

One consistent trend in the literature on haemoglobin in children is the tendency for haemoglobin to increase with increasing age.171920 This trend was also apparent for both high and lowland children (see results). However, the drop in haemoglobin levels seen in lowland girls after the age of 11-13 years may be due to the initiation of menstruation. This drop was, however, not seen in highland girls. Instead the haemoglobin levels were fairly leveled from the age of 9-11 years to the end of the study period. Taking into consideration that highland girls were heavier than lowland girls and in view of the strong relationship between body weight and the onset of menarche,21 it is possible that highland girls had begun their menarche at an earlier age of 9-11 years and the effect of this on haemoglobin levels was opposed by the hypoxic effect of high altitude. The effect of age on haemoglobin levels in children was thought to be due to the fact that children in the first few years of life have a negative iron balance because only less than 10% of the dietary iron is absorbed.20 In addition, child nutrient habit is usually low in iron, but with increasing age this habit gradually improves with the introduction of adult food which is rich in iron.20

Another finding of this study is the absence of significant differences in haemoglobin levels between boys and girls at either altitude before puberty. This finding agrees with observations from some parts of the world622 but at variance with reports from Jeddah18 and Jamaica.23 The investigators in these areas found significant differences in haemoglobin levels between boys and girls aged 5-11 years but no explanation for these differences were offered.

Finally, the impact of weight and height on haemoglobin levels in Saudi high and lowland children were identified. Tall heavy subjects tend to have higher values of haemoglobin levels. Similar patterns were observed in high and lowland men in the same area.24 However, in this study, weight and height could only explain 10% of the variation in haemoglobin levels in highland and lowland children (R2 adjusted = 0.1 for both boys and girls).

It is concluded that the significantly higher haemoglobin levels in highland children may be due in part to the polycythemic effect of chronic hypoxia of altitude and as well as the beneficial milder environmental conditions on the health of children.


The author would like to thank all staff including administrators, physicians, technicians and nurses in primary health centers who assisted in this study.


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Haemoglobin; Children; Altitude

© 2006 Journal of Family and Community Medicine | Published by Wolters Kluwer – Medknow