The rise of people with food allergies can be seen as quite paradoxical in today’s society- the increase in sanitation and improvement in healthcare should theoretically lead to a decrease in illnesses, yet countries that are less developed have far fewer people with diagnosed allergies. As well as this, there are now five times the number of peanut allergies compared to 1995 in the UK, helping to prove that this is an issue increasing with modernisation. Here, I will be exploring the theories as to where this rise has stemmed from, and also analysing why lactose intolerance is apparently incompatible with the other allergenic trends.
For some part, the reasoning is quite simply human natural selection being less effective in the modern era. In the past, any genetic based allergens would likely cause the sufferer to die young of anaphylactic shock, preventing them from passing on their genes to future generations. Now, the treatment and awareness surrounding allergens is so much greater that the occurrence of an allergic reaction is less frequent, and the number of people in first world countries that die of allergies is negligible. That would also provide some evidence for the world-wide disparity- places with minimal healthcare facilities have fewer allergy sufferers as those with allergies died too young of a reaction to pass on their genes.
While that provides a simple explanation, it does not explain many of the findings of researchers. Dr. Mark Holbriech instead proposed the ‘hygiene hypothesis’, after studying the Amish people. He discovered that while almost 50% of American children have a positive skin test (ie. had a reaction) to one of the major food allergens, only 7% of Amish children have. These children are in a closed farming community where they handle horses from a young age, drink unpasteurised milk and have no electricity. Holbreich theorised that this increased and more intense exposure (both in early life and while still in the womb) to microbials improves the natural development of immunoregulatory networks, which would decrease the risk of developing allergies. This would also help to explain the disparity worldwide, but proves that it is not the healthcare system that causes it- the Amish people live in various states in the USA and have access to some of the best medical treatment worldwide.
Another theory was due to vitamin D deficiency in the more Northern countries. Vitamin D induces antimicrobial proteins, protects the intestinal flora, improves the protective epithelial barrier in the gut and helps produce certain T cells. All of these improve the activity of the immune system- meaning that those that do not have a vitamin D deficiency are less likely to have allergies due to the improved immune regulation vitamin D provides. This theory was also backed up by a study showing that individuals born in Autumn and Winter (and therefore exposed to less vitamin D both in the womb and as babies) were more likely to develop allergies at this young age.
Strangely, the persistence of lactose intolerance is completely the opposite to the other allergens- yet the same reasons may be partially at play. Over 70% of the Asian population is lactose intolerant , whereas over 90% of the European population can consume lactose. However, this was not always the case. About 7000 years ago, it was thought that nobody was able to consume lactose products. However a single genetic mutation (13,910*T) that occurred around this time made it edible to the masses. Multiple researchers have speculated the reasons as to the rapid ‘spread’ of the mutation- originally thinking it to be due to the lack of vitamin D that people had in the North. Milk is a strong source of vitamin D, meaning that those who could consume milk were stronger and healthier, and therefore could bear more offspring who would inherit this gene; rapidly making most of the continent able to consume it.
That was found to not be the case in research conducted by University College London (UCL). By analysing DNA samples, they found that the first cases of being able to consume lactose were in central Europe, nearer to Spain. In Spain, there is much more sunlight- so the mutation would not be advantageous if the vitamin D theory was correct. It was therefore proposed by Paul Sherman (Cornell university) that the mutation was helpful due to milk being calorie and protein rich. It was also in constant supply, and was less contaminated than water. Most of the time, early dairy farmers would have only been able to consume fermented milk products (eg.cheese) as this had a much lower lactose content. However, in a famine, they would have turned to consume the higher-lactose products, causing diarrhea in the lactose intolerant individuals- which can be fatal when severely malnourished. This would explain why the spread of lactose persistent genes rose so rapidly.
As well as this, those that could drink milk were in better health, and caught fewer water-borne diseases (such as cholera), resulting in them living longer and breeding healthier children. In Africa and Asia however, deadly diseases of cattle were rife and their hot climates made it much harder to domesticate them- resulting in the genetic mutation being less advantageous. This therefore explains why the majority of people in these continents are not lactose tolerant.
In conclusion, the variance in lactose intolerance is fascinating as it describes the spread of a particular genetic mutation, as well as explaining some of the variations in cultural dishes- almost all European food contains milk products yet very little Asian cuisine does. In terms of the other food allergens, the ‘hygiene hypothesis’ and the ‘Vitamin D hypothesis’ do well to explain the rise in allergies in Northern locations globally, and can also provide a basis for beginning to slow these numbers via exposure to harmless microbes at a young age and ensuring that vitamin D levels are kept high in pregnant women and small children.
- “Why the world is becoming more allergic to food” https://www.bbc.com/news/health-46302780 BBC News, 2019.
- “Amish farm kids remarkably immune to allergies” https://www.reuters.com/article/us-kidsallergies/amish-farm-kids-remarkably-immune-to-allergies-study-idUSBRE8431J920120504. Reuters, 2012
- “Review Article Food allergy is linked to season of birth” https://www.sciencedirect.com/science/article/pii/S1323893018301783. Science Direct, 2019
- “Lactose intolerance – Genetics Home Reference” https://ghr.nlm.nih.gov/condition/lactose-intolerance. NIH, 2020
- “Early Europeans unable to stomach milk” https://www.newscientist.com/article/dn11261-early-europeans-unable-to-stomach-milk/. New Scientist, 2007
- “Dairying Barriers Affect the Distribution of Lactose Malabsorption.” https://www.researchgate.net/publication/247233461_Dairying_Barriers_Affect_the_Distribution_of_Lactose_Malabsorption. Research Gate, 2005
- “Lactose intolerance seems linked to ancestral struggles with climate control”https://news.cornell.edu/stories/2005/06/lactose-intolerance-linked-ancestral-struggles-climate-diseases. Cornell University, 2005
- “Famine, not calcium absorption, may have driven evolution of milk tolerance in Europeans” https://www.sciencedaily.com/releases/2014/01/140122091846.htm. Science Daily, 2014