Course:KIN366/ConceptLibrary/BodyMassIndex

Movement Experiences for Children
KIN 366
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Instructor: Dr. Shannon S.D. Bredin
Email: shannon.bredin@ubc.ca
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Body Mass Index (BMI) is a calculation based on an individual’s height and weight, commonly used as an indication of the objective relative size of an individual (Centers for Disease Control and Prevention, 2009). BMI calculations for adults and children (ages 2-20) differ in that for adults, values are compared against fixed thresholds of underweight and overweight. In children, BMI values are compared against percentiles for children of the same age and gender (Centers for Disease Control and Prevention, 2009).

Calculating BMI for Children

Calculation

BMI values for children and for adults are calculated as children often continue to grow until approximately 20 years of age (National Heart, Lung, and Blood Institute, 2013). For children, BMI values are calculated through dividing their weight in kilograms by the square of their height in meters (Dhir & Ryan, 2010). This calculated value is then plotted in a growth chart along with the child’s age and sex in order to obtain the percentile that the child is in (National Heart, Lung, and Blood Institute, 2013).

Growth Charts

Depending on the sex and age of the child, different growth charts are used. This is due to the large changes in body fat amount with age, as well as the significant differences in body fat between males and females (Centers for Disease Control and Prevention, 2014).

Growth charts are developed from a reference population, or child growth reference (National Obesity Observatory, 2011). Through measuring a large sample of children at different ages and sex, a reference for the distribution of BMI values of males and females at specific ages is developed.

The most commonly used growth charts in Canadian clinical settings are produced by the World Health Organization (WHO), called the WHO Child Growth Standard Charts (Dieticians of Canada, 2014). WHO growth charts are recommended because they were created based on breast-fed children raised to Canadian health and nutrition standards (Dieticians of Canada and Canadian Paediatric Society, 2014).

Types of Growth Charts

For newborn infants up until 24 months of age, a growth chart that that takes into account length, weight and head circumference is utilized (Dietitians of Canada, 2014).

For children from the ages of 24 months to 20 years, a separate growth chart that accounts for height and weight is used (Dieticians of Canada, 2014).

Children with certain developmental disorders such as Down’s Syndrome or Turner Syndrome are assessed using specialized growth charts typical of other children with the same developmental disorder (Lyon, Preece, & Grant, 1985; Myrelid, Gustafsson, Ollars & Anneren, 2002).

Percentiles

A percentile is a value that shows an objective measurement of where a child is in comparison with others (Hamill et al., 1979). If the weight of a 20-month old male is in the 60th percentile, it indicates that his weight is greater than 60% of males in that age group and lesser than 40% of males in that age group (Hamill et al., 1979).

Percentile Interpretations

By viewing where a child falls on a growth chart and calculating the percentile, interpretations can be made of whether a child’s measurements are within a healthy range.

Underweight: <5th percentile Healthy weight: 5th - 84th percentile At Risk For Overweight: 85th - 95th percentile Overweight: >95th percentile (Dietz & Robinson, 2005).

Usages of BMI Assessments

As BMI measurements are simple and fast, they are often used as the first step in assessment of possible weight issues in children (Dietz & Robinson, 2005). It is recommended that BMI calculations and growth chart plotting should be performed after birth at intervals of one to two weeks, one, two, four, six, nine, 12, 18 and 24 months, then once yearly for children from 24 months to 20 years of age (Dieticians of Canada and Canadian Paediatric Society, 2014).

Accurately plotted BMI measurements over a period of time reflect the growth pattern of a child. Within the first two to three years of life, it is normal for a child to shift one or two percentile curves up or down as the rate of growth often changes within early stages of life (Dieticians of Canada and Canadian Paediatric Society, 2014). Puberty is another period of time where sharp changes in growth rate are considered normal. However, with the exception of the above two periods, sharp increases or decreases in growth, or a flat growth line are potential signs of a growth disturbance (Dieticians of Canada and Canadian Paediatric Society, 2014).

Sequential measurements showing a sharp decline in the growth chart may be indicative of an impediment in growth, or failure-to-thrive (Dieticians of Canada and Canadian Paediatric Society, 2014). Contrary to this, serial measurements displaying a sharp upward growth may indicate a child developing overweight or obesity (Dieticians of Canada and Canadian Paediatric Society, 2014).

Limitations of BMI Usages

Although BMI calculations are often used in assessments of potential weight problems in children, it is important to note that they are not to be used as a diagnostic tool.

A significant limitation of BMI measures is that it measures excessive body weight, rather than excess body fat (Centers for Disease Control and Prevention, 2009). The objectivity of BMI allows for no distinguishing between adipose tissue and forms of fat-free mass such as muscle or bone (Centers for Disease Control and Prevention, 2009). As such, other forms of measurements such as skinfold thickness or waist-to-hip ratios may yield results more specific to body mass (Harvard School of Public Health, 2015).

High BMI Percentiles in Children

BMI values in the 85th – 95th percentile are considered “at risk for overweight” in children, and BMI values equal to or greater than the 95th percentile are considered “overweight” (Dietz & Robinson, 2005).

Causes of High BMI Percentiles in Children

There are a wide variety of reasons for why a child’s BMI percentile may fall in the “at risk for overweight” or “overweight” classification, including prenatal, genetic and environmental factors.

Prenatal Factors

Even during pregnancy, environmental factors have a significant association with the development of overweight and obesity in children. Small for gestational age (SGA) newborns, mothers with diabetes or mothers who smoked all produced an increased risk of children becoming overweight (Bradford, 2000).

Genetic and Family Factors

A family history of obesity is a significant predictor of a child becoming overweight and developing a high BMI percentile (Bradford, 2000). Having one obese parent doubles the risk of a child becoming overweight as an adult (Bradford, 2000). Children who were raised by single parents, or from families of low socio-economic status have increased risk of becoming overweight (Dhir & Ryan, 2010).

Dietary Habits

Dietary habits also play a crucial role in the development of overweight and obesity in children, as North Americans are increasingly consuming foods high in fat and sugar and eating with less fruits and vegetables (Epstein et al., 2001). There is also a readily available abundance of cheap, high-calorie and high-fat snacks and drinks, promoting snacking as a leisure activity and contributing to overweight and obesity in children (Bradford, 2000).

Physical Activity Habits

With the development of more electronic entertainment devices, children are spending less time participating in physical activity and more time watching television or playing video games (Dhir & Ryan, 2010). Children having more “screen time”, or time spent in front of a television, computer or electronic device screen is a strong contribution to the rising obesity and overweight rates in children (Dhir & Ryan, 2010).

Health Consequences of High BMI Percentiles in Children

Overweight children have stronger risk factors for a wide variety of adverse conditions. Children with high BMI have a greater number of risk factors for cardiovascular disease, such as hypertension and high cholesterol levels (Dietz & Robinson, 2005). Overweight children also have increased risk for mortality and morbidity later in adulthood (Contemporary Pediatrics, 2013). Additionally, children with high BMI values are at greater risk for developing obstructive sleep apnea, type II diabetes, chronic inflammation, increased blood clotting and endothelial dysfunction (Government of Western Australia Department of Health, 2014). Overweight children are also more susceptible to adverse psychosocial effects, such as depression, social isolation, negative self-perception and a higher risk of developing mental health issues in adulthood (Government of Western Australia Department of Health, 2014).

Motor Development Consequences of High BMI Percentiles in Children

High BMI is strongly associated with lower gross and fine motor acquisition, development and competence in children (Morano, Collela, & Caroli, 2011). Endurance performance during aerobic activities in children with high BMI is compromised as well (Morano, Collela & Caroli, 2011). The effect that overweight and obesity has on motor development is prominent even in childhood, as it was found that overweight infants were 1.8 times more likely than non-overweight to experience delays in motor development (Slining, Adair, Goldman, Borja, & Bentley, 2010).

Low BMI Percentiles in Children

BMI values that fall under the 5th percentile are classified as “underweight” (Dietz & Robinson, 2005).

Causes of Low BMI Percentiles in Children

There are many different factors that contribute to a child’s BMI falling in the “underweight” percentile, such as prenatal, socioeconomic, dietary and behavioral factors. Development of certain conditions and disorders may also cause a child to be underweight.

Prenatal Factors

Numerous factors during prenatal development have the ability to influence growth and development of children. Adequate maternal nutrition is an extremely important factor in healthy childhood development (Stanford University, 2015). Being born with a low birth-weight was also strongly associated with being underweight in childhood (Alasfoor et al., 2007). Infants born prematurely (being born before 37 weeks gestational age) are also strongly associated with significant motor impairment and being underweight in childhood (de Kieviet, Piek, Aarnoudse-Moens, & Oosterlaan, 2009). Pregnancy complications such as intrauterine growth restriction (IUGR), characterized by impaired fetal growth also commonly cause difficulties in development of an infant later in childhood (Barker, 2006).

Genetic and Family Factors

There are strong implications that genetic factors influence low BMI values in children. If one or both parents were underweight in childhood, their child is more likely to become underweight as well (World Health Organization, 2015).

Familial factors such as household income level also have strong influences on nutrition, and subsequently BMI of children. Poverty is a main cause of malnutrition and underweight children (World Health Organization, 2015). Low-income households are strongly linked to an increased risk of children becoming underweight due to insufficient nutritional intake (Casey, Szeto, Lensing, Bogle, & Weber, 2001).

Dietary Habits

Picky eating is a strong contributor to low BMI and underweight children (Anderson, 2011). As children often dislike eating healthier foods such as vegetables and prefer candies and sweets, this can lead to a decreased overall food intake as parents are often reluctant to give their children sweets to eat (Anderson, 2011).

Conditions and Disorders

Digestive conditions and other disorders may contribute to low weight gain in children, and subsequently a low BMI (Anderson, 2011). Gastro-esophageal reflux disease is a common chronic pediatric disease where stomach acid leaks upward from the stomach into the esophagus (Rudolph et al., 2001). This frequently leads to pain, repeated vomiting and refusal of food. Hypothyroidism and certain inflammations such as inflammatory bowel disease or cystic fibrosis may also lead to low BMI in children as well (Anderson, 2011).

Children, especially teenagers are susceptible to developing eating disorders such as anorexia nervosa or bulimia nervosa. These mental illnesses cause one to feel unsatisfied with their body and see themselves as overweight, developing an irrational fear of food and gaining weight (Smink, van Hoeken, & Hoek, 2012). Within the past decades, the incidence of eating disorders in the high-risk group of females aged 15-19 have steadily increased (Smink et al., 2012).

Health Consequences of Low BMI Percentiles in Children

It is common knowledge that underweight, or low BMI children are more susceptible to health problems as malnutrition weakens all cellular components of the immune system, causing a child’s body to be more vulnerable to illness (Rodriguez, Cervantes, & Ortiz, 2011). The nutrition of a child plays the largest role in nearly all health-related aspects of a child. Nutrition affects a child’s physical and cognitive growth, capabilities and ability to fight infections (Rodriguez et al., 2011). Children who have adequate intake of core macronutrients such as protein, carbohydrates and fats often possess strong deficiencies in cell-mediated immunity, leading to greater incidences of a wide variety of infections and disorders (Rodriguez et al., 2011). Furthermore, a main risk in underweight children is an increased risk of developing osteroporosis, a bone disease that causes an increased risk of bone fractures (Anderson, 2013).

Having a low BMI in childhood is correlated with increased morbidity and mortality rates. Severely underweight children who survive into adulthood are more likely to show lower intellectual and physical capabilities, as well as encounter difficulties during childbirth for women (Martorell, 1999).

Motor Development Consequences of Low BMI Percentiles in Children

Being underweight poses numerous difficulties to normal motor development in children. Children are often more frail and succumb more easily to illnesses, which negatively affect the amount of physical activity they partake in (Anderson, 2013). Children with low BMI percentiles show impaired development in gross and fine motor skills, as well balance, object manipulation and dexterity abilities (de Kieviet et al., 2009).

These impairments may create adverse effects in development of handwriting skills, and involvement in social activities centered on sport or physical activity (de Kieviet et al., 2009). Furthermore, compromised motor development also presents further risk for poor cognitive development and learning disabilities later in life (de Kieviet et al., 2009).

Practical Applications

It is well known that living an active lifestyle and receiving adequate nutrition is key in healthy overall development in children and attainment of a healthy BMI value. As such, early detection of potential weight problems and subsequent intervention are crucial in order to promote optimal development (Graf et al., 2003). Intervention and prevention implementations often have stronger results in younger children, as behaviors are more easily adaptable at a younger age (Government of Western Australia Department of Health, 2014).

Suggestions for Parents

Parents play a key role in the nutrition, health and BMI of their child, as they ultimately decide what types of food their children will eat. Preparing healthy foods like fruits, vegetables, lean meat and refined grains often can cause children to grow accustomed and learn to enjoy healthier foods (Dietz & Robinson, 2005). As children look mainly to their parents for guidance, modeling good eating habits will have positive effects on the nutrition of children. Parents can also participate in physical activity with their children, or encourage them to join sports teams at school or within the community. Limiting the time a child spends in front of the television or computer will help increase time spent partaking in physical activity, enabling a child to attain a healthy BMI value. Parenting programs that aim to educate parents on prevention of childhood overweight and obesity have also been shown to have a positive effect on weight management and prevention obesity in children (Government of Western Australia Department of Health, 2014).

Suggestions for School Systems

As many school systems have some form of cafeteria, snack bar or vending machine, removing unhealthy foods such as candy and chips high in sugar and fat will help reduce intake of these foods. Ensuring that a wide variety of healthy foods are offered at affordable prices will promote and encourage children to eat healthier, preventing the incidence of children classified as overweight (Dietz & Robinson, 2005). In a school-based study, it was shown that prevention of overweight and obese children can be done through replacing screen time with frequent and intense physical education classes (Dietz & Robinson, 2005). In addition, physical education and school sports not only contribute to lower incidence of overweight and obese children, but also to enhanced acquisition and development of motor skills as well (Armour et al., 2009).

Suggestions for Communities

Community promotion of active lifestyles also has strong effects on the knowledge, behaviors and attitudes in children regarding weight management (Government of Western Australia Department of Health, 2014). One such community group that exemplifies these views is “Participaction”, a non-profit organization with goals of promoting healthy living and physical fitness in Canadians, with many messages directed and tailored towards children and parents (Participaction, 2015). The physical design of a community, such as location and abundance of playgrounds, parks and trails also play a role in the activity levels of its inhabitants (Heart and Stroke Foundation, 2013). If such locations are more accessible, children will have more opportunities to engage in physical activity and subsequently maintain healthier BMI values.

References

1. Anderson, L. M. (2011). Approaches to the Underweight Child. Retrieved from http://learnpediatrics.sites.olt.ubc.ca/files/2011/11/underweight-child.pdf
2. Anderson, R. (2013). Underweight Kids at Greater Risk of Health Problems than Obese Children. Parent Herald. Retrieved from http://www.parentherald.com/articles/1143/20130513/underweight-kids-greater-risk-health-problems-obese-children.htm
3. Barker, D. J. (2006). Adult consequences of fetal growth restriction. Clinical Obstetrics and Gynecology, 49(2), 270-283.
4. Bradford, N. F. (2009). Overweight and obesity in children and adolescents. Primary Care: Clinics in Office Practice, 36(2), 319-339.
7. De Kieviet, J. F., Piek, J. P., Aarnoudse-Moens, C. S., & Oosterlaan, J. (2009). Motor development in very preterm and very low-birth-weight children from birth to adolescence: a meta-analysis. JAMA, 302(20), 2235-2242.
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