Pettifor John M
MRC/Wits Developmental Pathways for Health Research Unit, Department of Paediatrics, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
Ann Nutr Metab. 2014;64 Suppl 2:15-22. doi: 10.1159/000365124. Epub 2014 Oct 22.
Low dietary calcium intakes and poor vitamin D status are common findings in children living in developing countries. Despite many of the countries lying within the tropics and subtropics, overcrowding, atmospheric pollution, a lack of vitamin D-fortified foods, and social customs that limit skin exposure to sunlight are major factors in the development of vitamin D deficiency. Low dietary calcium intakes are typically observed as a consequence of a diet limited in dairy products and high in phytates and oxalates which reduce calcium bioavailability. Calcium intakes of many children are a third to a half of the recommended intakes for children living in developed countries, yet the consequences of these low intakes are poorly understood as there is limited research in this area. It appears that the body adapts very adequately to these low intakes through reducing renal calcium excretion and increasing fractional intestinal absorption. However, severe deficiencies of either calcium or vitamin D can result in nutritional rickets, and low dietary calcium intakes in association with vitamin D insufficiency act synergistically to exacerbate the development of rickets. Calcium supplementation in children from developing countries slightly increases bone mass, but the benefit is usually lost on withdrawal of the supplement. It is suggested that the major effect of calcium supplementation is on reducing the bone remodelling space rather than structurally increasing bone size or volumetric bone density. Limited evidence from one study raises concerns about the use of calcium supplements in children on habitually low calcium intakes as the previously supplemented group went through puberty earlier and had a final height several centimetres shorter than the controls.
膳食钙摄入量低和维生素D水平差是发展中国家儿童的常见现象。尽管许多国家位于热带和亚热带地区，但过度拥挤、大气污染、缺乏维生素D强化食品以及限制皮肤暴露于阳光的社会习俗是维生素D缺乏症发展的主要因素。膳食钙摄入量低通常是由于饮食中乳制品含量有限，而植酸盐和草酸盐含量高，从而降低了钙的生物利用度。许多儿童的钙摄入量仅为发达国家儿童推荐摄入量的三分之一到一半，然而，由于该领域的研究有限，这些低摄入量的后果鲜为人知。似乎身体通过减少肾钙排泄和增加肠道分数吸收来很好地适应这些低摄入量。然而，钙或维生素D的严重缺乏会导致营养性佝偻病，低膳食钙摄入量与维生素D不足协同作用会加剧佝偻病的发展。对发展中国家儿童补充钙会略微增加骨量，但停止补充后这种益处通常会消失。有人认为，补充钙的主要作用是减少骨重塑空间，而不是在结构上增加骨骼大小或体积骨密度。一项研究的有限证据引发了对习惯性低钙摄入量儿童使用钙补充剂的担忧，因为之前补充钙的组青春期来得更早，最终身高比对照组矮几厘米。
