Is milk good for your body?

Author: Mariko Morita

Editor: Naoko Matsumoto

I have a one-year-old son, and he is recently finishing breastfeeding.

While he is in nursery school, he usually drinks frozen breast milk and formula after a meal or at teatime.

I myself don’t like drinking cow’s milk with food, and so I have never needed mine at the mealtime. However, almost all nursery schools and elementary schools provide cow’s milk to children.

One plausible reason is the School Lunch Program Act in Japan. This law defines that a complete school meal consists of bread or rice, milk, and a side dish. However, in my opinion, a more likely explanation is that these facilities have just followed existing customs. So, what are the scientific grounds for recommending milk consumption among school-aged children?

The American Academy of Pediatrics recommends a 1-2 year old infant ingest around 480ml of milk a day. This is a great deal, isn’t it?

According to the American standards, infants are advised to take 500-800mg of calcium per day. In Japan, the Dietary Reference Intakes instructs that the daily calcium intake for 1-2 year olds should be between 400 and 500mg. In general, 100g of milk contains 110mg of calcium, so two cups of milk are required to meet this recommendation.

Numerous studies have demonstrated that milk is good for children’s growth. For example, researchers from Boston University tracked 106 children aged 3 to 5 from 1987 to 1999. (1) Those who ingested more dairy products while they were aged 3 to 5 had higher bone density at ages 15 to 17, compared with their counterparts.

Another study found that exercise and milk intake in childhood is reported to be important for elevating bone density (2). Moreover, a study conducted in Canada from 2008 to 2013 studied 2,831 children aged 1 to 6, and found that children with less milk consumption have smaller serum concentration of vitamin D.

Vitamin D helps you absorb calcium and maintain bone density. Almost all milk sold in Canada and the US is fortified with vitamin D. Thus, in those countries, milk is considered a source of vitamin D. Simultaneous intake of sufficient calcium and vitamin D would be beneficial for the growth of children.

In contrast, this is not the case with Japan, where most of the milk does not go through such adjustment. Usually, 100g of milk only contains 12 IU of vitamin D. Even, 500ml of these products contains just 60 IU of vitamin D. Infants aged one year or older need 600 IU of vitamin D a day.

Thus, this amount is only one tenth of their requirement.

Further, milk contains a really small amount of iron. The recommended daily iron intake for 1-2 year old children is 4.5 mg, but 100 ml of milk holds only 0.02 mg of iron.

If your child becomes full by drinking lots of milk, he or she may lose opportunities to take iron by food, which should be the main pathway for iron intake.

Given these profile despite the importance of getting the recommended amount of calcium, it may be an overstatement to insist the importance of taking milk to this end. Then, how about plant milk, for example, soy milk and almond milk?

You may have an idea that they are healthier than cow’s milk, but please don't believe this based on assumption. Indeed, plant-based milks are not necessarily healthier than cow’s milk. For instance, 100g of regular milk contains 100mg of calcium (there could be some variance among products), while 100mg of pure soy milk and almond milk holds 15mg and 75mg of calcium, respectively.

As for protein, 100g of regular milk contains 3.3g, the same amount of pure soy milk contains 3.6g, but only 0.6g of protein exists in 100g of almond milk. In this respect, soy milk or almond milk do not replace cow’s milk, as you cannot receive enough calcium or protein by those milks.

Moreover, soy milk may lead to too much intake of isoflavones. The microstructure of isoflavones is similar to female sex hormones. According to animal experimentations, isoflavones may have some adverse effects on animal reproductive function, although it remains to be seen whether it exerts similar influence on human beings. According to the current Japanese standard, daily intake of isoflavones should not exceed 70mg among adults. Children are not recommended to take isoflavones as supplements.

On average, 100g of soy milk holds 25mg of isoflavones. In addition, one 45g-package of sticky beans “natto”and 150g of soybean curd “tofu” contain about 37mg and 30mg of isoflavones, respectively. Although no recommendations have been made for safe intake of isoflavones in children, products like tofu, natto, and roasted soy flour “kinako” are easy even for infants to eat, and they are often used for baby food or infant food. Therefore, consumers understand that they can get plenty of isoflavones by eating such products. According to the American standard, infants are allowed to take less than 0.08 mg/kg of soy bean origin isoflavones. This means that, before eating baby foods, even a 10kg infant is allowed to have a maximum of 0.8mg per day.

Nonetheless, dairy products like milk are convenient foodstuffs for getting the required amount of calcium. For example, 150mg and 260mg of calcium exists in 100g of boiled Japanese spinach and canned mackerel brine contain, respectively. However, it’s quite difficult for infants to eat such amounts of vegetable and fish. There are lots of things to consider, including the environment where dairy cattle were raised and their feed. Yet, it is better to drink one or two cups of milk to prevent the shortage of calcium.

By the way, there is a condition called lactose intolerance syndrome. This is a congenital disorder consisting of an inability to digest milk and milk products. Particularly, when people with this disorder drink a lot of cold milk all at once, they often feel abdominal fullness and get stomach ache or diarrhea.

This is the reason why some people say that milk is not good for the Japanese people, where this disorder is prevalent. However, we can enjoy hot milk, without causing such symptoms, and can also drink cold milk, if taken slowly.

There is no reason why children with no symptoms of intolerance should refrain from drinking milk, and even most of the children with such symptoms can enjoy yogurt.

In any case, all foods should be consumed in moderation to maximize positive health effects.

It is important to eat a variety of foods in a well-balanced fashion, which leads to the intake of enough nutrition.

You can take calcium efficiently by drinking one to two glasses of milk a day, but it's also important to get calcium, iron, and vitamin D from other foods.

If your child is allergic to dairy products, you can use plant milk, and increase the variations of meals.

Of course, please don’t forget to give them calcium and protein from other foods.

References

1. Moore LL, Bradlee ML, Gao D, Singer MR. Effects of average childhood dairy intake on adolescent bone health. J Pediatr. 2008;153(5):667-73.

2. Golden NH, Abrams SA, Committee on N. Optimizing bone health in children and adolescents. Pediatrics. 2014;134(4):e1229-43.

3. Lee GJ, Birken CS, Parkin PC, Lebovic G, Chen Y, L'Abbe MR, et al. Consumption of non-cow's milk beverages and serum vitamin D levels in early childhood. CMAJ. 2014;186(17):1287-93.