By Ellen Feldman, MD
Altru Health System, Grand Forks, ND
Dr. Feldman reports no financial relationships relevant to this field of study.
- Responses to a questionnaire regarding consumption of cow and noncow milk, demographic information, and height measurements were obtained from 5,034 healthy children 2 to 6 years of age.
- After controlling for multiple variables, including gender and ethnicity, each daily cup of noncow milk reported consumed was associated with 0.4 cm lower height (P < 0.0001).
- This association with lower height appears partially explained by lower cow milk consumption.
- This study was observational and supports an association and not a causation; therefore, more research is needed.
Data from more than 5,000 Canadian children reveals a dose-dependent association between drinking noncow milk and lower height in early childhood.
Morency ME, Birken CS, Lebovic G, et al. Association between noncow milk beverage consumption and childhood height.
Am J Clin Nutr 2017;106:597-602.
The “Got Milk?” ad campaign of the early 1990s, launched to combat the decline in milk consumption thought to be related to increasing consumption of soda and juice, is known as one of the most successful ad campaigns of its time.1 However, by 2011, with the growing popularity of alternative noncow-based milk products, milk faced a new rival in the form of products such as soy milk, almond milk, and even noncow-derived animal milk.2
In an observational Canadian study, Morency et al examined the frequency and type of milk consumption in more than 5,000 children between 2 and 6 years of age who were enrolled in a primary care-based research study (Applied Research Group for Kids).3 The hypothesis of the study was that children who drank more noncow milk would grow slower or be shorter than their peers who drank the naturally more protein-rich cow milk. An additional goal of the study was to determine if consumption of cow milk mediated the difference in height — that is, if the difference in height was explained by lower cow milk consumption alone. Recruitment for the study was from primary care practices in Toronto. Exclusions included children with known growth difficulties and some chronic conditions. Interestingly, children with asthma were not necessarily excluded from the study.
Information about the number of cups of any noncow milk beverage consumed daily, the number of cups of cow milk consumed daily, age, sex, ethnicity, socioethnic background, and maternal height all were recorded, as was the height of each child. All noncow milk beverages were pooled together; no information was recorded regarding the specific type of drink in this category. For every participant, a height-for-age score was calculated using World Health Organization growth
standards.4
Out of 5,934 children included in the study, 4,632 drank a mean of two cups of cow milk daily (this included both cow-only and the blend group). Of the 643 primarily noncow milk drinkers, the mean consumption was 1.4 cups of noncow milk daily. In addition, 397 children drank both cow and noncow milk, and 156 did not consume any milk. (See Table 1.)
Table 1: Numbers of Cow and Noncow Milk Drinkers in the Study (n = 5,034)
|
|
Cow Milk Only
|
Noncow Milk Only
|
No Milk
|
Both Cow and Noncow Milk
|
|
Number of children
|
4,235
|
246
|
156
|
397
|
|
Percent of total
|
84.1%
|
4.9%
|
3.0%
|
7.9%
|
When studying height, children, and diet, there are clearly multiple factors to consider. Morency et al accounted for several potentially confounding variables, including age, sex, ethnicity, neighborhood/income, body mass index, and maternal height. The multivariate analysis of results showed an inverse, dose-dependent relationship, with higher noncow milk consumption associated with lower height.
Specifically, for each cup of noncow milk reported, the data reflected a 0.1 lower “height-for-age” score (P < 0.0001) or a 0.4 cm lower height/cup for 3-year-old children. This was mitigated only partially by cow milk consumption, as discussed later in this section. The trend appears reversed when looking at cow milk ingestion.
The second part of the analysis of these results involved efforts to determine if lower cow milk consumption alone could account for the height differences noted with noncow milk. Mediation analysis concluded that lower cow milk consumption can account only partially for this association. When adjusted for cow milk consumption, noncow milk drinkers still had lower height-for-age scores and lower height/cup at 3 years of age. (See Table 2.)
Table 2: Multivariate Analysis of Results
|
|
Mean Height-for-age Score
|
Mean Height/Cup Difference
Age 3 years
|
P Value
|
|
Cup/day noncow milk (any type)
|
0.1 lower
|
0.4 cm lower
|
< 0.001
|
|
Cup/day cow milk
|
0.05 higher
|
0.2 cm higher
|
< 0.001
|
|
Mediation analysis: noncow milk adjusted for less cow milk
|
0.08 lower
|
0.3 cm lower
|
< 0.001
|
COMMENTARY
This large-scale, observational study was straightforward in methodology, but more complicated in analysis. Pertinent data were obtained by a simple questionnaire asking how many cups of cow and/or noncow milk were consumed daily, and the data were supplemented by basic demographic information and height measurements. The supplemental information allowed control for significant potential confounders such as ethnicity, socioeconomic status, and maternal height — important contributors to a child’s height.
A closer look at the participants and exclusion criteria raises some questions. The inclusion of children with asthma in the study group may have slanted the results. Although Morency et al excluded children with most chronic disorders, they did not exclude children with asthma or report how many children fell into this category. Notably, youngsters with asthma may avoid dairy products to reduce triggers. Also, many children with asthma use inhaled corticosteroids to help control symptoms. There is an association between short-term use of corticosteroids in children and temporary growth suppression5; this may have influenced the results. Future investigations ferreting out these types of associations will be helpful in further understanding any association between noncow milk consumption and height.
Likewise, separating noncow milk products into subcategories according to type of beverage is essential to draw conclusions and make recommendations to families. It is possible that consumption of plant-based milk products (such as soy milk), nut-based milk products (such as almond milk), and noncow milk animal products (such as goat milk) all have unique association with height in children. We cannot determine this from the information reported in this study.
However, the current data make a strong case that children who consume more noncow milk in early years are shorter than age-matched peers, at least in the short term. There are no data or conclusions about long-term growth available from this study.
Morency et al noted that the most likely explanation for the association of lower growth with noncow milk consumption is that nutritional ingredients in cow milk, specifically proteins (casein and whey) and insulin-like growth factor 1 (IGF-1), contribute to height. Noncow milk lacks IGF-1 and typically contains less protein than cow milk. For example, one cup of cow’s milk contains 8 grams of protein, a similar quantity of soy milk usually contains 4-6 grams of protein, and there are only 2 grams of protein in one cup of almond milk.6 They also noted that neither the FDA nor the Food and Drug Regulations of Canada standardize the nutritional content of noncow milk as they do for cow milk, making it difficult to verify the nutritional value of these drinks.
Fortification of cow’s milk with vitamin D in particular, as well as other nutrients, is a standard in North America. Although noncow milk often is fortified, standards do not exist. Parents are wise to check labels carefully when planning to include these items as part of a young child’s diet. There are case reports of children developing nutritional deficiencies related to exclusive use of noncow milk as the beverage of choice; warning parents to be cautious in this regard is good practice.7
Finally, it is worth remembering that the results of this study indicated an association between noncow milk drinkers and shorter height in early life, but not about health status in general. It is important to note that while height and health may be linked in early development, this is not a dose-dependent relationship — that is, taller height at any one stage does not imply better health per se. Among other factors to take into consideration with consumption of dairy products is the potential of increased fat content; this may have adverse implications for health in children.
Notably, the same issue of the American Journal of Clinical Nutrition included an investigation by Ma et al looking at an association between adult height and healthy aging. Using data from the Nurses’ Health Study, Ma et al found a small but significant decrease in healthy aging associated with taller adult height.8 It appears the relationship between health and height is complicated and most likely is multifactorial.
A take-home message from this investigation can go beyond the association of noncow milk and lower height and approach a broader issue: the importance of inquiring about diet in young children when taking a medical history. It is interesting that almost 5% of the participants in this study of children younger than 3 years of age were drinking only noncow milk. When talking with parents of young children regarding choice of milk or beverage, consideration of diet is useful. If parents prefer giving noncow milk, it is reasonable to ask about other sources of protein and nutrients in their diet. Not only should a balanced and varied diet help with growth, but it also may set the stage for development of healthy eating habits later in life.
The integrative provider, equipped with a broadbased and holistic understanding of health and wellness, can put these research findings into perspective for parents. Noting that all milks are not “created equal,” understanding a child’s nutritional needs at each stage, and promoting a habit of checking nutrient labels are useful tools to help shape a healthy diet for young children.
REFERENCES
- Got Milk? A brief history. Available at: http://health.oregonstate.edu/sites/health.oregonstate.edu/files/moore-center/whole-grain-summit/day3/session10/1-got-milk-a-brief-history-06-26-15-final.pdf. Accessed Feb. 5, 2018.
- NPR. Why are Americans drinking less cow’s milk? Its appeal has curdled. Available at: https://www.npr.org/sections/thesalt/2017/05/16/528460207/why-are-americans-drinking-less-cows-milk-its-appeal-has-curdled. Accessed Feb. 5, 2018.
- Carsley S, Borkhoff CM, Maguire JL, et al. Cohort profile: The Applied Research Group For Kids (TARGet kids!). Int J Epidimiol 2015;44:766-788.
- Promoting optimal monitoring of child growth in Canada: Using the new World Health Organization growth charts — executive summary. Paediatr Child Health 2010;15:77-79.
- Loke YK, Blanco P, Thavarajah M, Wilson AM. Impact of inhaled corticosteroids on growth in children with asthma: Systemic review and meta-analysis. PLoS One 2015;10:e0133428.
- Consumer Reports. Choosing the right milk for you. Available at: https://www.consumerreports.org/cro/2014/08/milk-substitutes-should-you-sip-or-skip/index.htm. Accessed Feb. 5, 2018.
- Carvalho NF, Kenney RD, Carrington PH, Hall DE. Severe nutritional deficiencies in toddlers resulting from health food milk alternatives. Pediatrics 2001;107:e46.
- Ma W, Hagan KA, Heianza Y, et al. Adult height, dietary patterns, and healthy aging. Am J Clin Nutr 2017;106:586-596.
