Nutrition For Healthy Growth And Immunity

Nutrition for Healthy Growth and Immunity

Children are not small adults. They are constantly growing, developing and maturing from a neonate to a full-grown adult. Thus optimal nutrition is required to meet with the demands throughout this period so that full genetic potential can be realized.¹ Growth is the most commonly used functional outcome measure of nutrient adequacy.² Childhood growth not only involves an increase in body size but changes in body proportions, the relative sizes of organ systems and chemical compositions.¹ Epidemiologic data clearly show that patterns of growth in fetal life and infancy are correlated with later risk of cardiovascular disease and the metabolic syndrome.¹Thus optimizing nutrition in early life has relevance to long term health.

Normal Growth

The normal pattern of growth can be defined in the form of growth reference compiled by measuring normal healthy children. The data obtained may be reproduced graphically in the form of growth charts (such as NCHS, WHO, Agrawal growth chart) or be transformed into properties of a normal distribution as z-scores (such as WHO z scores). Weight, height (or length), and head circumference are the most widely used parameters clinically though other references commonly used are skinfold thickness, mid-arm circumference.¹ The pattern of growth can be resolved into infant, child, and pubertal phases based on endocrine influences.

Infant growth is primarily nutrient/insulin led, an extension of a fetal pattern whereas childhood growth is predominantly growth hormone led and pubertal growth is driven by the influence of sex steroids. Growth is affected by numerous factors including poverty, ethnic background and emotional well-being¹, Deviation from normal nutrition pattern can lead to over-nutrition (obesity) or under-nutrition (PEM).

During infancy by 1st year of life, the child increases in weight 3 fold and by 50% in length and in head circumference by 10 cm. The growth rate slows in the 2nd year of life and head circumference increases by 2 cm over the year and by 24 months, children are about half of their ultimate adult height. From 2-5 years of age, weight gain occurs about 2 kg/year, and height increases by 7-8 cm/year. Head grows an additional 5 cms between 3-18 years. From 6-11 years, weight gain averages 3-3.5 kg per year, and height increases by 6-7 cm per year. During adolescence, secondary sexual characters develop with acceleration in growth velocities with an increase in lean body mass to 90% in boys and decrease in girls to 75% as subcutaneous fat accumulates. Weight gain parallels linear growth with a delay of several months.³

Organ Maturation

Major organ maturation takes place in the brain, GI system, kidneys and metabolic activity as the child grows.

Neurological maturation:

Brain growth is maximum in the first 2 years of life with 90% of brain growth in three years and major psychomotor and mental development takes place during the same time. The brain utilizes glucose as its fuel and that is why glucose requirements are more in newborns as compared to adults. Thus appropriate timing and progression of complementary feeding are required for this process to continue uninterrupted.

Gastrointestinal maturation:

The gut is anatomically mature by 24 weeks of gestation, though there is no net transit through the large intestine. Enteral feeding is an important stimulus to gut maturation. Milk feeding especially human milk leads to both hypertrophy and hyperplasia of the small intestine due to the presence of peptide growth factors such as epidermal growth factor and lactoferrin in the colostrum. Early feeding also stimulates the release of gut hormones including cholecystokinin, motilin and enteroglucagon which respectively help to stimulate bile flow, intestinal transit and integration of liver metabolism with feeding. Pancreatic fat digestion is relatively immature at birth though the actions of lingual lipase and breast milk lipase helps to absorb breast milk lipids effectively. Breastfeeding also prevents gut infection by providing specific secretory IgA, other immune factors such as lysozyme, lactoferrin and lactoperoxidase as well as promotes colonization of large bowel by lactobacilli due to the prebiotic effect of non-absorbable oligosaccharides in breast milk.¹

Renal maturation:

At birth both GFR and renal tubular concentrating capacity is reduced. Carbohydrates and fats do not contribute to renal solute load. High proteins form urea that may not be well excreted by kidneys. Thus proteins in diet are gradually increased as kidneys mature.

Thus, nutrition varies as per the somatic phase of growth as well as on organ maturation.

Normal Nutritional Requirements

Energy:

Energy requirements are related to age, gender, body size and level of activities. Infants have a greater energy requirement as compared to adults primarily due to higher metabolic rates and special needs for growth and development. Sufficient carbohydrate is required to prevent ketosis and hypoglycemia (5 gm/kg/day) and enough fat to provide essential fatty acids (0.5-1 gm/kg/day of linoleic acid). Infants also require long-chain polyunsaturated fatty acids (LC-PUFA) such as arachidonic acid (ARA) and docosahexaenoic acid (DHA) for better visual and cognitive development. The minimal needs for carbohydrate and fat including LC-PUFA is around 1/3 of the total energy required in a day.⁴ Proteins should contribute 15% of daily energy requirement, carbohydrates 50% and fats 35% of which 6% should be PUFA.⁵

Proteins:

Infants require higher proteins per kg than an adult along with the higher proportion of essential amino acids (leucine, isoleucine, valine, threonine, methionine, phenylalanine, tryptophan, lysine, histidine) as well as cysteine,tyrosine and perhaps arginine.⁴

Electrolytes Minerals & Vitamins:

Vitamins and minerals are required for normal metabolic and growth functions of tissues, organs and bones. If protein intake is adequate, vitamin deficiencies are rare. If not, deficiency can result. Recommended daily allowance of various vitamins are depicted as follows:

Balanced Diet:

An infant should be on exclusive breastfeeds until 6 months of age with appropriate weaning food complementary to it after that. After 2 years of age, a diet consisting of fruits and vegetables, whole grains, low fat and nonfat dairy products and beans is advocated. In children who eat non-vegetarian food, fish and lean meal is advised.⁷

Nutrition & Immune System

Nutrition has a two-way influence on the immune system. The activities of the immune system exert a deleterious influence on nutritional status and alterations in nutrient intake modulate the intensity of the various activities of the immune system.¹

Effect of infection on nutrition:

With infection, muscle protein is catabolized to provide amino-acids to form new cells and proteins for immune response. Fat is also catabolized and fatty acids are released to satisfy the increased energy requirements of an infected person.

Gluconeogenesis also serves as a pathway for energy. Iron, copper & zinc are released from tissues to help wound healing. Acute-phase reactant proteins have released that help in immunomodulation.

Effect of nutrition on immune system:

Malnutrition influences virtually all of the components of the immune system with reduction of cell number and function of T-cell lymphocytes, shrinkage or impaired development of lymphoid organs (thymus, spleen and gut-associated lymphoid tissue) and suppression of some aspects of inflammatory response.¹ Total food deficit can lead to a reversal of CD4: CD8 ratio and decrease plasma complement level. The protein-energy deficit can suppress humoral and cell-mediated response, decrease tissue repair, and macrophage functions. Arginine deficiency can impair T-cell growth and development as well as thymic integrity whereas glutathione deficiency can decrease oxidant properties of leukocytes. Nucleic acid deficiency can suppress natural killer cell activity and cell-mediated immunity whereas impair recovery from sepsis. Supplementation of n-3 PUFA can decrease inflammation whereas saturated fatty acids can lead to immunosuppression. Copper & zinc deficiency also impair T-cell function and superoxide dismutase activity.¹⁰ In animal models, deficiency of vitamin E & A can impair both humoral and cell-mediated responses.

Thus, nutrition is an important determinant of immune responses. Nutritional deficiencies alter immunocompetence and increase the risk of infection which in turn leads to poor appetite and a vicious cycle.

Action of specific nutrients on growth & immunity

Proteins: Proteins serve as a source of energy and protein. Under-nutrition produces long term negative effects on growth and neurodevelopment (Kwashiorkor). Not only the quantity but the quality of protein is also essential. Protein under-nutrition also adversely affects immune function.²

Vitamin A: Higher morbidity and mortality rates due to vitamin A deficiency due to affection of physical epithelial barriers and secretory IgA in addition to ocular manifestations and growth retardation.⁶ Excess of vitamin A can also cause slow growth, drying of skin, hepatosplenomegaly, pseudotumor cerebri, alopecia and bone pains.

Vitamin D: Clinical manifestations of Vitamin D deficiency include rickets, hypocalcemic seizures impaired growth. Severe vitamin D insufficiency results in inadequate mineralization of the bones.

Vitamin B6: Vitamin B6 functions as a coenzyme in the metabolism of protein, carbohydrate and fat and deficiency in infants adversely affects growth. Deficiency can lead to dermatitis, microcystic anemia and confusion.

Calcium: Inadequate calcium requirement can lead to poor mineralization of bones and growth retardation.

Iron: Iron is present in hemoglobin, myoglobin, cytochromes in the body which serve metabolic, enzymatic and oxygen transport and storage in the body. Iron depletion leads to anemia and growth failure.

Zinc: Zinc deficiency results in poor growth impaired immune function, diarrhea and acrodermatitis enteropathica.

Iodine deficiency: Iodine deficiency is a major cause of impaired thyroxine synthesis and can lead to cognitive impairment, delayed bone age, growth impairment and neurological deficits.

Folic Acid: Folic acid deficiency causes megaloblastic anemia and impaired immunity.

Under-Nutrition

It may be due to inadequate proteins, inadequate energy and/or inadequate micronutrients. Problems of under-nutrition include growth failure, inadequate cognitive and social development diarrhea, infections, lower immunity (decreased cell-mediated immunity) chronic illnesses and specific micronutrient deficiencies. Poverty, food insecurity, low education level, lack of control of their time and resources are the main causes of under-nutrition. (8)

In response to this UNICEF/World Health Organization (WHO) care initiatives have identified six areas of care required for growth and development of young children.⁹

a) Care of women

b) Breastfeeding and feeding practices

c) Psychosocial care - Emotional support and cognitive stimulation for children

d) Food preparation

e) Hygiene practices

f) Home health practices

Nutritional Requirements at Different Life Stages

Infants: The first 4-6 months are a period of rapid growth and development. Breast milk contains all the nutrients required during this period. Exclusive breastfeeding should be encouraged until 6 months of age with the introduction of a weaning diet after that. Weaning food should meet the requirement of iron, proteins, thiamine, niacin, vitamin B6 & B12, magnesium, zinc, sodium and chloride.

1-3 years of age: Preschools are rapidly growing and have greater energy requirement. There is an increased need for all vitamins and minerals except Vitamin D & zinc. Lesser amounts of calcium, phosphorus and iron are needed as compared to earlier. Fiber (nonstarch polysaccharide) should also be added to meet the satiety needs. Protein requirements do not increase much.

4-6 years of age: Energy requirements continue to increase as well as proteins, vitamins *except C & D) and all minerals (except iron).

7-10 years: Energy, protein, vitamin and mineral requirements increase. Requirement for thiamine, vitamin C & D remains the same.

11-14 years: Protein requirement increases by 50%. The energy requirement continues to increase. Boys require increased vitamins and minerals whereas in girls iron requirement is very high and there is no change in the requirement of thiamine, niacin & vitamin B6.

15-18 years: Energy, protein, vitamin and mineral requirement increases with the same requirement of vitamin B12, folate, vitamin C, magnesium, sodium, potassium, chloride and copper. Calcium and iron requirement markedly increases.

Conclusion

Children are growing both physically and mentally and adequate nutrient supply is necessary to maintain the genetically programmed growth potential as well as immune system development. Impairment at both micronutrients as well as macronutrient levels can lead to maladjustment and improper growth and development with chronic long term health consequences.