The idea that drinking dairy milk is essential for good nutrition has taken a hit in recent years. Canadian milk consumption declined by 18% between 1995 and 2014. Several factors may explain this shift: the changing makeup of the Canadian population, concerns about the health impact of dairy products, concerns for animal welfare, increased allergies and intolerances. Growing preference for plant-based milks is also a factor.
Researchers at St. Michael’s hospital recently raised the alarm that drinking non-cow’s milk is associated with lower height in children. According to this study, published last week in the American Journal of Clinical Nutrition, for each daily cup of cow’s milk they drank, children were 0.2 centimetres taller than average. This begs the questions: why are those children taller, and is being taller actually healthier?
The study’s lead author, Dr. Jonathon Maguire, a pediatrician at St. Michael’s Hospital – whose ties to the dairy industry are detailed below – states that “Height is an important indicator of children’s overall health and development. Cow’s milk has been a reliable source of dietary protein and fat for North American children, two essential nutrients to ensure proper growth in early childhood. But many parents are choosing non-cow’s milk for their children, which may have lower nutritional content.
On their website, St Michael’s Hospital states that “The study did not examine why children who drank non-cow’s milk were shorter on average than those who drank cow’s milk, however the authors hypothesize that children who drink non-cow’s milk may consume less dietary protein and fat than those who drink cow’s milk, resulting in reduced growth.” Unfortunately this is an unsubstantiated hypothesis.
“It is not possible to know, from the results of this study, the impact of protein and fat intake on the children’s growth.”
The researchers did not measure protein or fat intake. It is not possible to know, from the results of this study, the impact of protein and fat intake on the children’s growth. Children who drank non-dairy milk may have been consuming other rich protein sources from foods, such as lentils, beans, nuts and seeds. Some of the children may have been eating meat, fish, eggs and poultry. They could have even been consuming other dairy products such as cheese or yogurt. So it is not possible to make assumptions about diet quality. In fact, children who are consuming adequate calories are almost certainly meeting their protein and fat requirements through a varied diet.
Another problem with this study is that the non-dairy milks were grouped together, even though they have very different characteristics. Any milk other than cow’s milk, including goats milk, soy milk, rice milk, etc., were all grouped for the analysis. Dr. Maguire said: “For example, two cups of cow’s milk contains 16 grams of protein, which is 100 per cent of the daily protein requirement for a three-year-old child, according to the study. Two cups of almond milk beverage typically contains 4 grams of protein, which is only 25 per cent of the daily protein requirement for a three-year-old, who may not be receiving sufficient protein from other dietary sources.” Although this calculation is correct, Dr. Maguire could have chosen to compare soy milk instead. Fortified soy milk is the dairy alternative recommended in Canada’s Food Guide. It has protein and calcium levels almost equivalent to cow’s milk.
Along with protein and fat, cow’s milk also contains insulin-like growth factor-1 (IGF-1). This hormone helps cells to grow and divide, and so promotes growth and development in children and continues to have anabolic effects in adults. The IGF-1 found in cows is the same as that in humans. In the paper published in the American Journal of Clinical Nutrition Maguire and the other authors acknowledge the potential role of IGF-1 as a factor in growth promotion. Boosting levels of IGF-1, is not necessarily desirable, however, as high levels of IGF-1 have been linked to increased risk of cancer. In fact, height is associated with modest decreases in the likelihood of healthy aging.
So, it seems that attaining greater height may not even be a desirable characteristic; especially if it is promoted by increasing a hormone that may also cause overgrowth of cancer cells. This research should not cause parents to have caution about giving non-cow’s milk to their children. If anything, it just opens up greater questions about the health of cows milk as a beverage for any of us.
Dr. Maguire’s paper is part of a research collaboration between St Michael’s Hospital and The Hospital for Sick Children called TARGet Kids! According to the project website, “The aim of the TARGet Kids! registry is to link early life exposures to health problems including obesity, micronutrient deficiencies, and developmental problems.”
The website also shows that TARGet Kids has received financial support from the dairy industry in the form of multi-year grants from the Danone Institute and the Dairy Farmers of Canada. It has also come to light that Dr. Maguire was first author on another study funded by the Dairy Farmer’s of Canada investigating low milk intake, Vitamin D deficiency and fracture risk in young children. It has been reported by Ars Technica that Dr. Maguire was a member of the Dairy Farmer’s of Canada Expert Scientific Advisory Committee until 2016.
It is unfortunate that these industry ties were not reported in the study’s press release or the ensuing media coverage.
Pamela Fergusson, RD PhD is a vegan dietitian in private practice in Toronto, and a lecturer in the School of Nutrition, Ryerson. Pamela promotes the use of plant-based milk in her practice as a healthy and safe part of a balanced plant-based diet.