Lactose Intolerance – Where did it Originate
If you are of European descent (more than 70% of us in New Zealand are) and lactose-tolerant a new study may shed some light on the question of how your ancestors gained that trait.
The study analysed DNA from 230 West Eurasians who lived between 6500 and 300 BC and explains how adult Europeans inherited the ability to drink milk from Russian herders.
Lactose intolerance is an inability to digest the sugar (lactose) in milk. It is caused by a deficiency of the enzyme lactase that allows lactose to be broken down into simpler sugars that can then be absorbed into the bloodstream. If you are lactose intolerant and drink a glass of milk the undigested lactose begins to ferment in the gut causing diarrhoea, gas, bloating and stomach cramps.
Babies and young children produce lactase and can digest the lactose in mother’s milk. But as they grow older, most switch off the lactase enzyme. Only 35% of the human population can digest lactose beyond the age of about 7 or 8. And most people who retain the ability to digest milk can trace their ancestry back to Europe.
It is about 10,000 years ago that humans started domesticating animals for food in The Middle East. At that time, people still lacked the genetic mutation that would have allowed them to digest lactose after childhood. So these early farmers couldn’t drink raw milk but they learned how to reduce lactose levels to a minimum by fermenting milk to make cheese or yogurt.
The study explains that Europeans descended from three different groups: Stone-age hunter-gatherers, farmers who migrated from Anatolia (Turkey) and nomadic herders (pastoralists) who migrated west from the Great Steppe in Russia. Somehow a genetic mutation occurred in the Russian herders’ population that switched the lactase-production gene permanently to the “on” position. This mutation is then introduced into northern and western Europe when the Russian herders invade those regions about 4,000 years ago.
DNA testing these days can tell us exactly how big a portion of our genetic make-up comes from either of these three ancestries (hunter-gatherers, farmers and herders). A clear north-south gradient of lactose tolerance frequency can be found in Europe. The further north we go (UK, Scandinavia) the more pastoralist traits we find and as a result most people (90%) there are lactose tolerant. The Mediterranean population shows much less pastoralist traits and as a consequence southern Europeans are less lactose tolerant (40-50%).
Note: A lactose intolerance adaptation took place in West Africa and southwest Asia as well. However, these occurred independently from the European mutation.
Study: Genome-wide Patterns of Selection in 230 Ancient Eurasians (Authors: Dr. Bastien Llamas, senior research associate at the Australian Centre for Ancient DNA , The University of Adelaide and colleagues).
For more information on lactose tolerance listen to the interview with Dr. Bastien Llamas which was broadcast on Monday, 25 January 2016: http://www.radionz.co.nz/national/programmes/nights/audio/201786738/digesting-dairy
Maria is one of our highly talented resident Naturopaths and Medical Herbalists. She has over 13 years experience in complementary medicine and co-founder of Advanced Naturopathics, a Naturopathic clinic in Christchurch. She uses a variety of non-invasive modalities including nutrition, herbal medicine, homotoxicology and Bicom bioresonance therapy.