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Monday, July 15, 2013

Vitamin D and breast fed infants

The diet of choice for infants during their first 6 months of life is exclusive breast milk. Not only is breast milk sterile and loaded with the exact nutrients an infant needs, but it also has an array of immune strengthening factors from maternal antibodies to complex carbohydrates, which promote a very health colonic microflora. Of late, however, breast milk has come under the spotlight of paediatric nutritionists because of concerns about vitamin D status in breast-fed infants. The level of exposure to sunlight largely determines vitamin D levels in blood. Thus vitamin D levels are highest as we enter winter following summer and autumn and are lowest as we enter summer following the darkness of winter and the emerging sunshine of spring. Given the high level of worry that people have about skin cancer, the use of sun blocks and possibly combined with poor dietary choices has led to quite a high frequency of low blood levels of vitamin D among adults. This has been linked to several metabolic disorders such as obesity and diabetes and these are topics, which have been extensively covered in previous blogs.

Whilst it may or may not be a problem for adults to have low levels of vitamin D in blood, it becomes an issue for mothers who are exclusively breast feeding their babies, particularly where infants are protected from UV sunlight with very high UV protection factors in sun blocks. In such cases, the infant may have insufficient dietary vitamin D and the American Academy of Pediatrics[1] have issued guidelines on the use of vitamin D supplements for exclusively breast fed infants recommending that they receive 400 International Units of oral vitamin D per day until they are weaned at 6 months.  This recommendation, issued in 2008, effectively doubled the previous recommendation and sought to ensure that the level of vitamin D in the blood of breast fed infants is at a level considered at the present time to be optimal to prevent rickets.

A recent paper published in the Journal of the American Medical Association[2] set out to directly explore the impact of varying oral doses of vitamin D on infant blood vitamin D levels. The infants were all breast fed and the study used four doses of oral vitamin D supplements (400, 800, 1200 and 1600 International Units) The study was a randomized double blind study in that infants were randomly assigned to one of the four treatments and neither the pediatric team nor the parents knew what actual dose was being given to each child. However, an independent safety monitoring officer was charged with inspecting all data as it emerged and on the instruction of this independent monitor, the dose of 1,600 IU per day was abandoned because this dose led to very high levels of blood vitamin D. Such high levels can cause calcification of soft tissue where calcium is inappropriately sequestered into non-bone or soft tissues such as the arteries and heart. All infants in this group were then re-assigned to the lowest group (400 IU/day).

The primary outcome expected by the researchers was to identify the level of vitamin D supplementation, which would lead to a blood level of vitamin D of 75 nano moles per liter in 97.5 % of infants. The results showed that this target was achieved by only 55% in those on the standard dose (400 IU/day). This % increased to 81% of infants on the 800 IU/d dose and 92% on those given 1,200 IU/d. The abandoned dose of 1,600 did achieve the target but of course was also found to increase the risk of soft tissue calculation. In effect, the study doses failed to deliver the expected outcome.

What does all this mean? To this blogger, sitting as I am now in a rare Irish heat wave, the sun is not evil. It should be respected but not feared. Obsessive use of sun protection by adults and by parents on their children and infants lies at the heart of this problem. Titrating the complex links between the levels of vitamin D in parental blood, in breast milk and in infant blood is just too complex even for clever pediatricians.  Mothers who use the sun sensibly and who allow some sun exposure to their infants, should have no problem with vitamin D deficiency in their exclusively breast fed babies. If they have any concerns, it is they who should take vitamin D supplements or enjoy butter, oily fish and liver. The level of vitamin D in plasma, which is the target of the American Academy of Pediatrics, is achieved by only 55% of infants. We urgently need studies to understand why this is so. How much is due to sun fear and how much is due to maternal nutrition? What do we know about formula fed infants? Why was such a group not included in this study? This is all a work in progress.

[1] Wagner CL (2008), Pediatrics, 122, 1142-1152
[2] Gallo S et al (2013) JAMA, 309, 1785-1792

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