Myths about milk – Should adults drink it?

Prof. RNDr. Aleš Macela, DrSc.
Prof. RNDr. Vanda Boštíková, Ph.D.

(Part I.)

Humans are mammals. From birth, in the early stages of life, breast milk is their only source of nutrition. It is therefore surprising how many myths and misconceptions exist about milk, even if they do not directly concern breast milk [1]. Let’s take a look at the most common misconceptions and half-truths and their explanations.

Myth 1: “Milk is not suitable for humans; it is the only mammal that drinks it in adulthood (except for domesticated cats). In adulthood, it should basically not be drunk at all.” This is what 21% of Czechs believe, arguing that all other mammals in nature feed on milk until they triple their birth weight. For humans, this would mean a period of up to one year of life [2]. Another argument is the health problems people experience after consuming cow’s milk. These include lactose intolerance or allergy to milk proteins, which are not the same thing. Approximately 65% of the world’s population has a reduced ability to digest lactose, i.e., milk sugar, a disaccharide composed of glucose and galactose. This phenomenon is more common in people of Asian, African, and Hispanic descent. In Europe, it affects approximately 20% of the population. In the Czech Republic, lactose intolerance affects about 10% of people [3, 4].

Myth explanation: Humans need calcium for their health, and not just for healthy bones. Calcium is found in many foods, but not all sources provide it in a form that can be used by the body. The usability of calcium, i.e. its soluble form, varies between different foods. Of the total amount of calcium in milk, 32.4% can be used, in cheese 32.8%, and in yogurt 25%. Most plant sources, such as cereals, soybeans, legumes, spinach, rhubarb, sorrel, and tea, contain calcium, but it is difficult to dissolve and therefore unusable by the body [5]. There is one exceptional, whose calcium is absorbable in approximately the same amount as calcium in milk. Milk is therefore the dominant source of calcium for humans. However, if a person experiences health problems after consuming milk, this is a problem for that individual and not for humans as a species.

The so-called lactose intolerance of some people is a remnant of our ancient ancestors. It is said that about five thousand years ago, no adult was able to digest milk properly. They lacked lactase, an enzyme that breaks down lactose into metabolically easily usable sugars, glucose and galactose. Then changes occurred in the genome, particularly on the second chromosome, which led to the maintenance of lactase production into adulthood and thus to tolerance of milk as a nutritional source. In just a few thousand years, this change became so widespread in the European population that milk lactose tolerance is now dominant among Europeans, and drinking milk in adulthood no longer causes major problems. The prevalence of lactose tolerance varies considerably between regions and ethnic groups.

The ability to digest lactose is most common among people of Northern European origin. To a lesser extent, it is found in some parts of Central Asia, the Middle East, and Africa [6, 7]. However, what initiated the change from intolerance to tolerance of lactose is still a matter of debate. One possibility is adaptation to the domestication of dairy animals around 10,000 years ago. This is countered by the fact that people in Central Asia have historically drunk milk and consumed dairy products and do not have lactase tolerance, which has not developed. The most likely explanation seems to be the pressure of living conditions on human populations living in different areas of the Earth. Stressors such as famines, serious epidemics, or changes in living conditions could have acted independently or together and become a signal for changes in the human genome. Selection pressure then fixed this change in the population [8-11].

In addition to lactose intolerance, health problems associated with milk consumption include milk allergy, which is one of the most common food allergies [12, 13]. This is an undesirable hypersensitive immune response to milk proteins, mainly casein or serum β-lactoglobulin, which are abundant in milk, along with other allergens [14]. Milk allergy, which is most commonly mediated by immunoglobulin E, affects about four percent of infants. It is very rare in adults [15].

So, what is the answer to the question: Should adults drink milk? Despite the problems some people experience after consuming cow’s milk, it is good to drink milk. It is an irreplaceable natural source of calcium and contains a whole range of other biologically active elements, such as iron, zinc, potassium, and selenium [16], as well as a range of B vitamins (thiamine/B1, riboflavin/B2, niacin/B3, all three pyridine derivatives/vitamin B6, cobalamin/B12), as well as vitamins C and E and traces of vitamin D [17]. Drinking milk and consuming dairy products is beneficial for the health of older people [18].

Literature

1. https://www.vyzivaspol.cz/vyziva-a-potraviny-myty-a-realita/myty-o-mlece/
2. https://www.vitalia.cz/clanky/myty-a-povery-o-mlece/
3. https://www.menimecukrovkupohybem.cz/diety/bezlaktozova/procento-lidi-s-intoleranci-na-laktozu-percentage-of-people-with-lactose-intolerance/
4. https://www.denik.cz/zdravi/intolerance-laktozy-20200629.html
5. https://zeny.iprima.cz/zdravi/vapnik-jake-zdroje-jsou-pro-nas-opravdu-nejprinosnejsi#
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*This text has received support from the National Recovery Plan under project 1.4 CEDMO 1 – Z220312000000, Support for increasing the impact, innovation, and sustainability of CEDMO in the Czech Republic, which is financed by the EU Recovery and Resilience Facility.