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Key nutrients

Iron

Iron is an important component of haemoglobin and myoglobin and is therefore essential in the transport and storage of oxygen. In the infant, iron is important for its involvement in many central nervous system processes that could affect infant behaviour and development1.  However, iron deficiency is the most common single nutrient disorder globally2, and infants are at a particular higher risk due to their rapid growth and high iron requirements3.

An infant is born with a store of iron that will last until approximately 6 months of age. Once an infant is 6 months, their iron stores have run out and they require more iron from their diet. They will get a significant amount of iron from breastmilk or formula milk and can now also have iron-rich solid foods introduced to their diet.

There are two forms of iron; haem-iron and non-haem iron. Haem iron is the most bioavailable form of iron (20-30% absorption)4, and is found in animal food sources including offal, red meat, poultry and eggs. Non-haem iron is less bioavailable (5-15% absorption)4, and requires the assistance of ascorbic acid (vitamin C) for its absorption in the body5. Non-haem sources of iron include pulses (peas, beans, lentils), dark green vegetables, and iron-fortified cereals and milks. Once an infant has been weaned on to solid foods it is important that a variety of the above foods are included in their daily diet so as to meet their increased need for dietary sources of iron.

The clinical definition for Iron deficiency anaemia (IDA) is haemoglobin (Hb) level <110g/l (while low iron stores is classified as a serum ferritin <10g/ l)6 . The immediate symptoms associated with IDA include pallor, fatigue, poor appetite, muscle weakness and increased susceptibility to infections, in the short term.  However the long term implications of IDA are even more detrimental and have been shown to negatively impact on cognitive development and behavioural outcomes, even after corrective iron therapy. A study by Lozoff et al 2000 reported on the long term effects of Iron deficiency in adolescents, ten years after corrective treatment. In this study, significantly more of the children who had chronic IDA in infancy, displayed lower scores for mental and motor functioning and were 3 times more likely to repeat a grade relative to their iron replete peers. The IDA group were also more likely to have a behavioural difficulty with greater incidence of anxiety, depression and /or attention deficit disorders being reported7. These are really compelling findings and warrant our attention as similar effects of IDA have been reported in other intervention studies.8-11

Vitamin D

Vitamin D is essential for optimal bone growth as the active metabolite dihdroxyvitamin D, plays a key role in calcium homeostasis. Dietary sources of vitamin D are essential for efficient absorption of calcium in the intestinal epithelium.  Few dietary sources exist for example oily fish (salmon, herring, mackerel, trout, and fresh tuna), shellfish, eggs and fortified foods such as milks. Due to the limited dietary availability the main source of vitamin D comes from the action of sunlight on skin. However, due to Ireland’s temperate climate and most especially, its northern latitude, very little sunlight is available for vitamin D activation on the skin, particularly in winter months12. This coupled with sun avoidance and the more vigilant use of sun protection creams results in vitamin D absorption becoming compromised and can lead to sub-optimal vitamin status.  This also means there is a greater reliance on dietary sources of vitamin D to ensure vitamin requirements (RDA’s) are met. The RDA for vitamin D is 8.5µg/d for 0-6 months of age and 7µg/d for infants aged 7-12 months of age.

The clinical syndrome associated with vitamin D deficiency is known as rickets, which is a softening of the bones due to inadequate vitamin D intake resulting in poor calcium / phosphorus absorption. Certain ethnic groups such as those with darker skin colour (Asian & African populations) have reduced ability to convert vitamin D to its active form on skin. This places these individuals at increased risk of developing rickets or other skeletal deformities14-15. However, as vitamin D deficiency becomes more widespread, skeletal deformities such as rickets and osteomalacia are now beginning to re-emerge in children born in the UK and Holland16-17. Over the past decade there have also been a few reported cases of rickets in Ireland which has lead to the development of a national guideline for vitamin D supplementation of 5ug/d for all infants.12 Research has shown vitamin D deficiency is extremely common in Ireland and affects all population groups including, teenagers, pregnant and lactating women and the elderly. However, a lack of vitamin D during a period of rapid growth, such as infancy and toddlerhood, is likely to have the greatest negative impact on healthy bone development. Given the lack of appreciable dietary sources it is therefore, very important that toddlers consume vitamin D-fortified foods such as some breakfast cereals, fortified milks and margarine. Since 2010, the Health Services Executive have introduced a national policy on the implementation of vitamin D for all babies. All babies should receive a 5ug (200IU) daily supplement containing vitamin D from 0-12 months of age20.

  1. Beard JL & Connor JR. Iron status and neural functioning. Ann Rev Nutr. 2003;23:41-58
  2. Beard J & Stoltzfus R.  Iron-deficiency anemia: re-examining the nature and magnitude of the public health problem. J Nutr. 2001;131:563S-703S
  3. Leung AKC & Chan KW. Iron deficiency anemia. Adv Pediatr. 2001:48:385-408.
  4. Martinez-Torres C & Layrisse M. Iron absorption from veal muscle. Am J Clin Nutr.1971;24:531-40.
  5. SACN 2009. Draft SACN report on iron and health, June 2009.
  6.  Freeman VE et al. A longitudinal study of iron status in children at 12, 24 and 36 months. Pub Hlth Nutr 1998;1: 93-100.
  7. Lozoff B et al. Long-term developmental outcome of infants with iron deficiency. N Engl J Med.1991; 325(10):687-694.
  8. Lozoff B et al. Long-term developmental outcome of infants with iron deficiency. N Engl J Med. 1991.325(10):687-694
  9.  Walter T et al Cognitive effect at 5 years of age in infants who were anemic at 12 months: a longitudinal study. Pediatr Res. 1990;28:295.
  10. Roncagliolo M et al. Evidence of altered central nervous system development in infants with iron deficiency anemia at 6 mo: delayed maturation of auditory brainstem responses. Am J Clin Nutr. 1998;68(3):683-690.
  11. Aggett PJ et al. Iron metabolism and requirements in early childhood: Do we know enough?: A commentary by the ESPGHAN Committee on Nutrition. J Pediatr Gastro & Nutr.2002:34 337-345
  12. Recommendations for a national policy on vitamin D supplementation.  FSAI Publication report 2008
  13. Recommended daily allowances for Ireland: FSAI Publication, 1999
  14. Lopez SN et al. Rickets in Asian immigrants. An Esp Pediatr. 2002;57: 227-30.
  15. Wharton B et al. Rickets. Lancet. 2003;362:1389-400.
  16. Gregory JR et al. National Diet and Nutrition Survey: Children aged 1½ to 4½ years. London: HMSO, 1995.
  17. Hulshof K, et al. 2002. Food consumption of young toddlers in the Netherlands – The nutrient intake survey. Zeist, The Netherlands; TNO Voeding (ISBN 90 5177 0383)
  18. Hill TR, et al, Prevalence of suboptimal vitamin D status in young, adult and elderly Irish subjects. Ir Med J. 2006.99(2):48-49
  19. Cashman KD. Vitamin D in childhood and adolescence. Postgraduate Medical Journal. 2007. In press
  20. Health Services Executive (2010). Policy on vitamin D Supplementation for Infants in Ireland

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