Lactose intolerance: what is lactose intolerance, types and causes of this condition?

What do we know about lactose intolerance? A summary of its characteristics and types.

Lactose intolerance is defined as a disorder that appears in the patient after he/she ingests a product containing lactose (a disaccharide that is present in dairy products).

It is a condition widely distributed in the world, since depending on the age group and ethnicity analyzed, up to 65% of the population may present it. It is interesting to know that the prevalence of this intolerance depends largely on the ethnicity of the individual, since African Americans, Asians and Latinos have a greater predisposition to suffer from it. This is due to genetic factors that we will see later.

It is estimated that in the United States alone there are 30 to 50 million lactose intolerant people. It is not surprising, therefore, that countless research studies have been conducted on this pathology since its discovery in the 1960s.

Join us on this journey through the world of lactose intolerance, as this condition dates back to ancient times. this condition dates back to ancient times and has certain and presents certain characteristics that will surprise you.

The biological basis of lactose intolerance

Before assessing the global situation of this disorder and how it is distributed throughout the population, we need to establish certain bases as far as the causes of the disease are concerned.

As mentioned above, lactose intolerance is a pathology that occurs when the affected individual is unable to digest the sugars present in milk, resulting in intestinal discomfort, abdominal bloating, gas and diarrhea.

It is interesting to know that Lactose is the primary carbohydrate that makes up milk (including human milk).. Physiologically speaking, this disaccharide sugar cannot be absorbed by the intestine of our species, so we require the action of the enzyme lactase, a type of β-galactosidase that is responsible for breaking down this complex sugar into the monosaccharides glucose and galactose.

This all-important enzyme is synthesized in the brush borders of villi cells in the small intestine, but unfortunately, it has been observed in the small intestine.Unfortunately, however, it has been observed that in mammals there is a physiological decrease in lactase secretion with age. This responds to a clear mechanism at an evolutionary level: milk is the first food we ingest at birth, but it is natural that over the years an adult individual resorts less and less to this source of nutrients so difficult to obtain in a non-industrialized world. For this reason, it is normal for the body to save energy by skipping the abundant production of this enzyme.

Types

Lactase enzyme deficiency can be congenital or acquired over the years. Depending on the underlying reason for the pathology, four types of lactose intolerance can be described:

1. primary lactase deficiency 2.

This is the most common cause of lactose intolerance.. Epidemiological studies show that, for example in Mexico, 30% of adults have this type of deficiency. Symptoms begin to appear after the ingestion of dairy products in the adolescent stage or during adulthood, since the decrease of the lactase enzyme begins in childhood and continues throughout the individual's life.

Although it is an acquired condition, it is of essential importance to emphasize that it is a genetic disorder, i.e. there is a predisposition to it from birth, although it does not manifest itself during the first years of development.

2. Secondary lactase deficiency

Various diseases can damage the mucosa of the small intestine, which naturally results in a decrease in lactase enzyme production.. Some pathologies that can trigger this secondary deficiency are gastroenteritis, celiac disease, Crohn's disease, ulcerative colitis or the use of certain drugs and chemotherapy.

3. Other causes

We can list two other causes, which although much less common, are present in the population. Congenital deficiency is a special case in which the newborn is not able to digest dairy products due to an autosomal recessive mutation..

On the other hand, developmental deficiency is caused in infants born prematurely, as their small intestine is not fully formed and lactose hydrolyzing activity is compromised.

How does it affect different populations around the world?

This is a topic of special interest to any epidemiologist, as few disorders manifest themselves in such a clear pattern according to the ethnic group studied. As much as the concept of "race" in the human sphere is in disuse due to lack of consensus and moral application, the fact that our species reports genetic variations according to the place of development and family lineage is undeniable..

This is why, during the last 10,000 years, a series of mutations have been observed in certain population groups that allow their members to secrete lactase at adequate levels during their adult life. The variant of the gene encoding lactase activity is inherited in a Mendelian dominant manner, so it is not surprising that this resistance is highly present in certain regions.

It is fascinating to learn that that this series of mutations has been favored in populations that have been in intimate contact with dairy cattle over thousands of years of evolution. of evolution. Due to this natural selection mechanism, lactose intolerance is distributed as follows:

• Northern European populations have only 15% of lactose-intolerant members (at most).
• In certain population groups of Asian and Indo-American descent, the prevalence of this disorder rises to almost 100 %.
• It is estimated that 65 % of the world's population is lactose intolerant.

As we can see, this series of data shows that the consumption of dairy products over the centuries appears to be an important factor in quantifying lactase production in an adult individual. This is a clear a clear mechanism of natural selection from a theoretical point of view, since the useful mutations are fixed over the generations, and the deleterious ones disappear.and deleterious ones disappear.

From the paper, theories based on a natural selection mechanism make all the sense in the world: adults capable of digesting cattle milk correctly would obtain more calories with less effort than the rest, so it is to be expected that they would have more and better offspring in a general way and these genetic mutations would be presented in the following generations.

Lactose intolerance in ancient times.

In addition to the very interesting data presented above, scientific reports have demonstrated that lactose intolerance was already present in humans during the Bronze Age, about 3000 years ago..

The study of the DNA of the skeletal remains of 14 individuals belonging to this period allowed modern scientists to discover that, indeed, these human beings did not carry the relevant mutations for a correct production of lactase in the adult individual.

Other studies indicate that the first European farmers also did not carry these mutations 8,000 years ago.. The most widely accepted theory is that these genetic variations spread throughout the population as animal husbandry became a general practice and dairy products were consumed more and more frequently. In any case, these new reports indicate that at least 6,000 years passed between the first livestock farmers and the widespread development of lactose resistance (at least in the populations analyzed), a fact that is very difficult to explain.

Summary

As we have seen, lactose intolerance is a disorder that goes far beyond the patient's Gastrointestinal discomfort.. It is a pathology of great epidemiological and evolutionary interest, as it is very difficult to explain the fact that certain human groups began to drink milk assiduously as adults if, clearly, they were not prepared for it as a species.

Studies like the ones we have shown you today raise more questions than answers, since explaining the exact origin of the mutations that allowed the development of lactose tolerance and its role in different societies is complex to say the least. Of course, spaces like this do nothing more than highlight the thousands of unknowns that continue to enclose the human body.

Bibliographical references:

• Harvey, L., Ludwig, T., Hou, A. Q., Hock, Q. S., Tan, M. L., Osatakul, S., ... & Muhardi, L. (2018). Prevalence, cause and diagnosis of lactose intolerance in children aged 1-5 years: a systematic review of 1995-2015 literature. Asia Pacific Journal of Clinical Nutrition, 27(1), 29.
• Intolerancia a la lactosa, MayoClinic.org. Recogido a 6 de octubre en https://www.mayoclinic.org/es-es/diseases-conditions/lactose-intolerance/symptoms-causes/syc-20374232
• National Institutes of Health. (2006). Lactose Intolerance: Information for Health Care Providers. US Department of Health and Human Services, 1-6.
• Swagerty Jr, D. L., Walling, A., & Klein, R. M. (2002). Lactose intolerance. American family physician, 65(9), 1845.
• Warrior skeletons reveal Bronze Age Europeans couldn’t drink milk, sciencemag.org. Recogido a 6 de octubre en https://www.sciencemag.org/news/2020/09/warrior-skeletons-reveal-bronze-age-europeans-couldn-t-drink-milk