Cow's milk is the primary source of vitamin D for children, but dairy products can interfere with the absorption of iron. Pediatricians have never known how much milk a child should drink. Now researchers have established that for most children, two cups a day achieves the right balance.

牛奶是儿童获取维生素D的主要来源，但是乳制品会阻碍铁的吸收。一直以来，儿科医师并没有明确了解儿童牛奶的饮用量应为多少。如今，研究人员发现，对于大多数儿童而言，每天两杯牛奶（总计500毫升——编注）便可以达到合理的平衡。

Canadian scientists studied more than 1,300 healthy 2- to 5-year-olds, collecting data on diet and physical activity. They took blood samples to measure iron and vitamin D levels.

加拿大科学家调查了1300多名两岁到五岁的健康儿童，收集了他们的饮食和运动数据，并且抽取了儿童血液样本来测量铁和维生素D的含量水平。

The study, published online in the journal Pediatrics last week, found that after adjusting for other factors, two cups a day was enough to maintain sufficient vitamin D (more than 30 nanograms per milliliter of blood) without affecting iron levels. But bottle use, season of the year, skin pigmentation and body mass index had significant effects on the optimal amounts of milk. Children with darker skin, for example, needed three to four cups of milk to get sufficient vitamin D in winter. Those who used only a bottle failed to maintain sufficient stores of vitamin D and iron.

这项研究于上周在《儿科》(Pediatrics)期刊的在线版刊登。该研究发现，在调整其他因素之后，每天两杯牛奶的摄入量完全可以维持充足的维生素D储备（每毫升血液中超过30微克），同时不影响铁含量。但是奶瓶的使用、季节、肤色和体重指数对于牛奶的最摄入量有着非常大的影响。例如，肤色较深的儿童在冬天需要饮用3到4杯的牛奶才能保证充足的维生素D摄入量。那些只喝一瓶奶的儿童则难以维持足够的维生素D和铁含量水平。

The lead author, Dr. Jonathon L. Maguire, an assistant professor of pediatrics at the University of Toronto, said that children over 2 should not be given a bottle. "It's easy to give children the bottle to pacify them," he said, "but in terms of these two nutrients, there's no benefit in it."

多伦多大学(University of Toronto)儿科学副教授、该研究作家乔纳森·L·马奎尔博士(Dr. Jonathon L. Maguire)指出，两岁以上的儿童不应再使用奶瓶。他说，“家长喜欢拿奶瓶来安抚孩子。但是就这两种营养物质的吸收而言，奶瓶喂奶是没有益处的。”