Topic of the Month
The role of micronutrients at all stages of life
By Julia Bird
Micronutrients are amazing molecules! They are needed in only very small quantities – the daily intake of vitamins B12, D and K is less than a grain of fine sand – yet they are absolutely essential for life. No matter how young or old we are, we need micronutrients every day to keep us healthy. Nutrient needs change, however, and babies have different requirements compared to seniors. Which micronutrients are most important at each stage of life?
The first steps to good nutrition start before birth (1). Micronutrient malnutrition can affect fetal development, so it is important for women who could become pregnant to eat a healthy diet. The most important micronutrients for babies before birth are folic acid, vitamin A, iron, iodine and omega-3 fatty acid docosahexaenoic acid (DHA).
Folic acid is needed for proper development of the nervous system: if pregnant women are deficient in the first weeks of pregnancy, their fetus is at risk of neural tube defects. Folates are needed in the body to make DNA, and folate deficiency can interfere with the normal development of the neural tube by reducing the proper formation of DNA in neural cells during this period of rapid growth (2). Food fortification and dietary supplementation with folate have been instrumental in reducing the number of neural tube defects in many countries (3).
Before birth, vitamin A is one of those micronutrients needed in the right amount: both too little and too much can be harmful (4). Vitamin A is needed in cells that are undergoing rapid cell division, and deficiency can cause birth defects (5). On the other hand, very high intakes of pre-formed vitamin A (retinol) during the first 7 weeks of gestation can also cause birth defects. Pregnant women should keep their intakes within the recommended intake range.
There is a great demand for iron during pregnancy. The developing baby needs iron in its red blood cells, and healthy iron levels are beneficial for pregnant women to prevent illness from blood loss during childbirth. Unfortunately, iron deficiency anemia is a risk factor for preterm birth and low birth weight (6). Anemia causes stress in the infant and mother, which increases risk of preterm labor and (pre-) eclampsia (7).
DHA is an omega-3 fatty acid that is incorporated into cells of the nervous system (8). It is a conditionally essential fatty acid, but unlike other essential fatty acids, intakes during pregnancy are often lower than recommended (9). Recent evidence supports prenatal supplementation improving preschoolers’ cognition (10).
A critical micronutrient in pregnancy is iodine (11). Iodine makes up part of the thyroid hormones, and deficiency is the major preventable cause of mental retardation in the world. The iodine content of foods is highly variable and related to the iodine content of soils. Iodized salt fortification is the most effective means to increase the iodine intake of populations (12).
Infancy and toddlerhood
The early years of life are ones of great transitions: the first food of infants is milk, but as babies start to explore and interact with the world, their diet diversifies. Very young children have a high rate of growth and therefore iron and vitamin A are extremely important (13, 14). The essential fatty acids DHA and ARA should be supplied in the diets of all infants and young children as they play a critical role in normal visual and neurological development (8, 15). Globally, toddlers have inadequate intakes in vitamins A, D, E and calcium (16). Micronutrients vitamin D and fluoride gain importance in the early childhood years.
Vitamin D is needed by the body to absorb calcium from the digestive tract. The disease that is caused by vitamin D and/or calcium deficiency in childhood is called rickets, which is characterized by soft, weak bones. After decades of the disease being under control, rickets is re-emerging as a public health problem due to reduced sun exposure (17). Attention should be paid to providing infants and toddlers with adequate vitamin D and calcium.
Fluoride is a mineral that is incorporated into the surface of developing teeth. This is a process that can only happen in childhood, when teeth are being formed. Low fluoride levels in drinking water are associated with greatly increased risk of dental caries (18). The micronutrient fluoride is important in maintaining dentition throughout the life span.
Children gradually learn independence, and good nutrition supports them on their journey. Adequate iron intakes remain important, as do intakes of calcium and vitamin D for healthy, growing bones. Iodine deficiency is a global problem in school-aged children: around one in three has an inadequate iodine status (19). Untreated iodine deficiency leads to intellectual delays in children (20). Families with young children should use iodized salt in cooking; for families who rarely use salt in cooking, a supplement may be beneficial. Globally, children are at greatest risk of low vitamin E status (21).
A major part of childhood revolves around school and learning. The brain undergoes a growth spurt in children aged 7 to 9 years, in the DHA-rich area of the brain that is responsible for higher-order cognitive functions (22). There is a growing body of evidence that supports a role for the long chain omega-3 fatty acid DHA in helping schoolchildren learn better, particularly those vulnerable to poor school performance (22, 23). Throughout childhood and adolescence, an adequate intake of DHA supports normal brain development (24).
After the high growth rate in infancy, adolescence is the next big jump in development. This occurs at a time when adolescents are starting to establish their independence, including making changes to their diet that may not be ideal. Critical micronutrients for adolescents include calcium, iron, vitamin C and folate.
Calcium is the main mineral in bones, and the growth spurt that occurs around age twelve to thirteen means that adolescents undergo the greatest increase in bone mass in their lives during this period. An adequate calcium intake is instrumental in building the bone mass that will be important for the rest of their lives. Dairy products make the most important contribution to intakes, and adolescents who skip the glass of milk for a soft drink are at risk of calcium intakes that are too low.
Since folate is important for the synthesis of DNA, RNA and proteins, the high growth rates of puberty increases the need for folate. Daily intake recommendations reflect this. A representative study of the U.S. population found that adolescents had the poorest folate status of all age groups, regardless of whether folate fortification of flour had been implemented (25), and in European adolescents, folate intakes were found to be too low (26). Poor nutrition behaviors such as skipping breakfast, or avoiding leafy vegetables, can have a large impact on folate intakes. In addition, vitamin C is a risk nutrient for adolescents, particularly older adolescents.
While adults generally are at lower risk of vitamin or mineral deficiency as they are no longer growing and the diseases of old age are years away, they still may be at risk of micronutrient deficiency. This may be partly due to lifestyle choices. Smokers have an increased requirement for vitamins C and E (27, 28). Excessive alcohol intakes affect the metabolism of various vitamins, particularly folate, vitamins B1 and B3 (29-31). Vitamin B6 deficiency was found to be the most common vitamin deficiency in the United States (32), most likely due to inadequate intakes (33). Poor vitamin B6 status was also seen in several surveys conducted in European adults (34-36).
Iron deficiency is a worldwide issue, and women of childbearing age are at greatest risk due to menstrual losses (37). Adolescent and adult women need to ensure that their intakes of iron are adequate. In particular, women should try to consume highly absorbable iron, or include a source of vitamin C with their meals to maximize absorption (38).
Older adults are at risk of general malnutrition. Age-related changes in smell, dentition and hunger sensation, combined with high rates of chronic disease and reduced mobility can mean that seniors have a reduced intake of nutrient-dense foods and the micronutrients they contain (39). The costs of micronutrient malnutrition in the elderly are a considerable burden on national health care spending in many countries. Last month, NUTRI-FACTS reviewed nutrients important to maintaining cognitive health in aging, however seniors have other important nutrient needs.
Older people have an increased requirement for vitamin D to offset a greater likelihood of vitamin D deficiency (40), yet remain at greatest risk of a low vitamin D status. Vitamin B12 deficiency rates are elevated in older people. This is due to age-related changes in the digestive tract that reduce the production of stomach acid and other digestive fluid components needed to absorb vitamin B12 (41). Treatments for some conditions common in older patients, such as metformin for type 2 diabetes, may also induce vitamin B12 deficiency (42). Mild vitamin B12 deficiency contributes to cognitive impairment.
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