4. ANTHROPOMETRY FOR POLICY AND PLANNING

Anthropometry is the study and technique of taking body measurements. It is used widely to measure the nutritional status of individuals or populations. This chapter outlines how anthropometric research can be used for assessing nutrition problems, examines key considerations in anthropometric assessments and presents several applications of anthropometry in reducing risks in different population groups.

Uses of anthropometry

Anthropometric assessments are useful because they provide a simple and practical way of describing the overall nutritional status of the population groups. Their usefulness stems from anthropometry's close correlation with the multiple dimensions of individual health and development and their socio-economic and environmental determinants.¹ Information on energy and nutrient intakes from food consumption studies will help in the aetiologic interpretation of deviant anthropometry and the planning of appropriate dietary interventions for targeted groups.

Anthropometric studies can help identify nutritional problems such as undernutrition and overnutrition and pinpoint groups with specific nutritional and health needs to be addressed in policy development and programming.² Anthropometric indicators can define the extent of the problems and can be used as one criterion in ranking areas and population groups by need, in this way allowing the targeting of appropriate interventions and informing decisions on resource allocation.¹ Where interventions are expected to influence nutrition directly or indirectly, anthropometric measures may be used to evaluate progress and the outcome of an intervention.

The application of anthropometric measurements in the assessment of child growth, and investigations of the relation between malnutrition and mortality are well documented.^{1, 3, 4} Increasingly, attention is being directed to the use of anthropometry in the assessment of overweight, obesity and body fat distribution and the risk of chronic diseases.⁵

While anthropometry measures may help to indicate the existence and extent of nutritional problems, and also serve as markers of risk of ill-health, the information does not, by itself, identify specific causes of nutritional problems or the underlying factors that explain the association between anthropometric status and subsequent risk of morbidity and mortality.¹ This is the major limitation of anthropometry as changes in body measurements may be sensitive to several factors including energy and nutrient intakes, infection, activity levels, altitude, stress and genetic background.⁶ The findings of anthropometric studies, however, can help to increase awareness of nutrition problems and can provide useful starting points for the investigation of these problems. Repeated surveys using similar statistically selected representative samples can be used to assess trends over time and the relationship of such trends to socio-economic conditions and dietary and other lifestyle habits.¹

Key considerations in anthropometric assessments

CUT-OFF POINTS FOR INDICATORS

Anthropometric indices are essential for the interpretation of measurements: a value for body weight alone has no meaning unless it is related to an individual's age or height.⁷ The indices are derived through combinations of measurements. For example, measurements of weight and height may be combined to produce the body mass index (BMI) (weight/height²) or weight may be related to height through the use of reference data.

An indicator is often derived from indices, with the imposition of a cut-off point to estimate population prevalence.¹ Cut-off points can also be used to characterize changes and trends within the population and identify persons at higher risk of adverse outcomes.

STUDY DESIGN AND SCOPE

The study design selected - including the question of who should be measured and the type of anthropometric indicator - will depend on the purpose of the survey and the type of information required for planning. In anthropometric assessments of populations, sampling should be on a representative basis, particularly when the findings will be used to determine the extent and severity of problems of public health significance, targeting of interventions, and estimating the degree of coverage (percentage of intended beneficiaries being covered) of interventions.¹ In certain circumstances, a sample of convenience may prove adequate. For instance, in most Caribbean countries, primary-school attendance is high and an anthropometric study of all school entrants may be representative of this target group.

In children, causes and correlates of deviant anthropometry are age dependent; therefore the selection and interpretation of indicators also depends on age.¹ For example, up to the 1990s in the Caribbean, when the primary focus of nutrition studies was on protein-energy malnutrition and mortality risk of young children, the age group of priority was from birth to two years, and most interventions were targeted at mothers, infants and young children. More recently however, this focus has shifted and increased attention is given to estimating the prevalence of obesity in all groups, especially adults, and the development of preventive strategies.⁸

QUALITY CONTROL

If survey findings are to lead to effective decision-making on policy and programme development, they should be based on the correct interpretation of anthropometric indicators and also on high-quality anthropometric data. This is where quality control is essential: taking accurate anthropometric measurements is a skill requiring specific training. There are a number of useful references with detailed information on the planning of anthropometric studies including the correct techniques in measurement, and the training and supervisory procedures required for quality control in the field.^{9, 10}

Applications of anthropometry in reducing nutritional risks at different stages of the life cycle

BIRTH WEIGHT

Anthropometric studies can be applied to reduce nutritional risks at different stages of the life cycle. For example, birth weight influences anthropometric status in early childhood. Low birth weight (defined as birth weight less than 2500 g) is associated with a range of both short- and long-term adverse consequences.¹¹ The aetiology of low birth weight is complex but poor nutrition both before and during pregnancy is recognized as an important contributory cause, especially in developing countries. Most of this evidence was based on pre-pregnancy nutritional status assessed by using anthropometric criteria and the adequacy of dietary intakes during pregnancy.¹¹ Pre-pregnancy weight and gestational weight gain are considered useful predictors of risk of low birth weight.¹²

INFANCY AND EARLY CHILDHOOD

Infants and pre-schoolchildren represent the most nutritionally vulnerable group. It is universally accepted that anthropometry is the most useful tool for assessing the nutrition status, and risks of poor health and survival of these groups. A combination of inadequate dietary intakes and infections are major contributory factors to impaired physical growth and mental development.¹³ Growth retardation in early childhood is linked to socio-economic conditions and living standards. Assessing growth, using anthropometric measures, not only serves as a means of evaluating the health and nutritional status of children but is also regarded as a sensitive indicator of differences in overall socio-economic development at a population level.¹⁴

Three anthropometric indices are commonly used to assess infants and children: length-for-age (or height-for-age), weight-for-age, and weight-for-length (or weight-for-height).^{1, 7} These have biological interpretations which may change with age. It is recommended that anthropometric measurements made in studying populations should be reported in relation to international standards; the reference standards developed by the US NCHS are recommended for international use by the WHO.^[3] Secondly, the measurements should be related to the reference population by standard deviation scores (Z-scores). Children with a Z-score below -2SD are considered moderately or severely malnourished, irrespective of the indicator used.⁷

Stunting, which is a low length or height-for-age index, is usually an indication of long term malnutrition. Stunted growth reflects a process of failure to reach linear growth potential as a result of suboptimal health and/or nutritional conditions.⁷ On a population basis, high levels of stunting are associated with poor overall economic conditions and increased risk of frequent and early exposure to adverse conditions such as illness and/or inappropriate feeding practice. Similarly, decreases in stunting rates are usually indicative of improvements in socio-economic conditions. At the population level, weight-for-height and height-for-age may be useful for identifying sub groups with a high prevalence of wasting or stunting for directing resources to resolve the problems. In evaluating the effectiveness of interventions, it is usually better to use stunting rates of children less than two years of age because the effects of the long-term adverse conditions may not be reversible in older children.¹⁰ High height-for-age has little public health significance.

Children with a low weight-for-age index are described as being underweight. The index is influenced by the height and weight of a child and is thus a composite of stunting and wasting, making interpretation of this indicator difficult.^{7, 15} The index can be used to assess changes in the magnitude of malnutrition over time but will have limited usefulness in decisions on the type of interventions required in specific settings. High weight-for-age is seldom used for public health purposes because other indicators, such as high weight-for-height are more useful in the evaluation of overweight as a proxy for obesity.⁷

Low weight-for-height helps to identify children suffering from current or acute undernutrition or wasting.⁷ This condition reflects a recent and severe process that has produced a substantial weight loss, usually as a consequence of acute shortage of food and/or severe illness. Chronic dietary deficit or disease can also lead to wasting. The index is appropriate for examining short-term effects such as seasonal changes in food supply or short-term nutritional stress brought about by illness.¹⁰ A high weight-for-height is considered an adequate indicator of obesity in young children on a population level.⁷

Anthropometric studies conducted in the English-speaking countries of the Caribbean during the last thirty years have documented the substantial reduction in childhood malnutrition.¹⁶ Reports in the early 1960s established malnutrition as one of the two major causes of infant and child mortalities at that time. Later findings from anthropometric studies confirmed the magnitude of the problem, and led to the implementation of interventions to improve child health and survival. These included:

• the improvement in the distribution of health care, particularly the strengthening of primary-care services;

• the introduction of growth monitoring/promotion activities at child health clinics;

• the provision of supplementary food for malnourished or at-risk children;

• improving formal and informal educational opportunities.¹⁶

The Barbadian experience in combating childhood undernutrition is described in Box 4.1.17 Findings from national anthropometric surveys helped in problem identification and led to the design and implementation of interventions for improving child health and nutrition.

SCHOOL-AGED AND ADOLESCENCE

The physical growth of schoolchildren aged six to nine years is the result of the interaction between environmental and genetic factors.³ The risk of undernutrition still exists where adverse environmental conditions are experienced before puberty. In countries undergoing a nutrition transition, the level of overweight and obesity is increasing in children and adults.¹⁸

The anthropometric indices used for pre school children can also be applied to school-aged children and adolescents. An accurate interpretation of anthropometric indices in adolescents is difficult because of the variability in patterns of growth and maturation. During adolescence, hormonal changes accelerate growth in height and as a result nutrient requirements are increased significantly above those in the childhood years.³ The body mass index (BMI) is recommended as the basis for anthropometric indicators of thinness (<5th percentile NCHS/WHO BMI for age) and overweight (> 85th percentile).³

Height census data of schoolchildren have been used for planning, evaluation and advocacy in Central America. Trend data for Costa Rica showed a decline in stunting rates from 1979 to 1997, indicating a sustained improvement in the quality of life.¹⁹ A food and nutrition security policy that was developed during this period included targeted interventions to disadvantaged groups. In Belize, the height census revealed that stunting was more than three times more prevalent in rural areas than in urban areas.¹⁹ This information led to the implementation of community-level interventions for

Anthropometric data from the Caribbean have highlighted the emergence of overweight and obesity in children and adolescents.^{21, 22} The reasons for the increase are not fully understood but appear to be related to sociocultural factors and changes in lifestyle practices. A comparison of actual body size, as measured by anthropometry, with perceptions of body image among adolescents in Trinidad was useful in identifying attitudinal patterns, which must be taken into account in the development of preventive strategies for combating the problems of overnutrition.²²

ADULTHOOD

Body mass index (BMI) is also commonly used to classify underweight, overweight and obesity in adults. The cutoff for undernutrition or thinness is 18.5, and that for overweight is 25.0 (see indicators in Chapter 5).3 The waist-hip ratio (WHR) is used to identify individuals at increased risk from obesity-related illnesses due to abdominal fat accumulation. It is now suggested that waist circumference (WC) alone may provide a more practical correlate of abdominal fat distribution and associated ill-health.²³ Age-specific prevalences of high WC or BMI in a population can be used to assess the overall health burden associated with obesity.⁵

Although anthropometric assessment techniques and cutoffs for elderly people do not differ from those used in adults, height measurements can be problematic. The interpretation of anthropometric indicators as predictors of risk may also differ with increasing age.³

The increasing prevalence of obesity in adults in the English-speaking Caribbean countries, as revealed by BMI-based classifications from anthropometric studies, has led to an increased awareness of its importance as a major public health problem in the region.²⁴ The problem has been recognized by national governments and efforts to address it are being pursued at a national and regional level.²⁵

Information on key social and behavioural determinants of high BMIs point to the need for a multisectoral approach in the development of appropriate public health interventions. One such intervention (described in Box 4.3) is targeted at school-aged children and seeks to promote positive lifelong habits of dietary and physical activity patterns.²⁶