A common problem of huge significance and cost, hidden in full view!
The world data shows that a great many adults experience Lactose Intolerance and yet, I at least have never heard it mentioned by my doctors even when I was seeking advice about Irritable Bowel Syndrome (IBS). Moreover, years ago, when I discussed one of my first serious episodes of diarrhea associated with eating ‘extra’ yoghurt, neither of the two very senior G.I. researchers considered Lactose Intolerance!
If you – like most people – go shopping in the dairy section of a Supermarket (in Australia), you may find a small supply of two or three types of Lactose-free milk, perhaps two types of Lactose-free yoghurt and one type of Lactose-free ice-cream. There are also often some soy and non-dairy substitutes but these few – and often well hidden products – are placed in what is usually a very large ‘dairy section’. So clearly they are intended for the specialised purchaser and not the majority (who probably need them)!
Are people unnecessarily suffering from Osteoporosis?
I was inspired to write this blog today because, while playing golf on Friday, we were discussing Osteoporosis and my very fit friend who had been told that her bone density was getting too low, admitted that she avoided dairy foods because they ‘upset her’ stomach! So, like a large proportion of the adult population, she was avoiding her best source of dietary calcium and developing a dangerous medical condition!
The LCT (Lactase gene)
This gene encodes the enzyme lactase, which breaks down lactose (the sugar in milk) in the small intestine. However, unlike most genes, this gene usually becomes inactive in adults!
All normal babies express high levels of lactase to digest breast milk. In most mammals — including most humans — this activity declines after weaning because it’s ‘not needed‘ once milk is no longer the main food source!
MCM6 (Regulatory control for LCT)
The real switch for adult lactase production lives not in LCT itself but in a regulatory element within a neighbouring gene called MCM6. Specific DNA variants (SNPs) in this control region determine whether LCT keeps being expressed into adulthood. Without worrying about the details, the world map (below) shows areas of ‘green’, where most people have ‘lactase persistance’ and can digest lactose for their whole life. The ‘red’ SNP shows regions where the majority of the population lose the gene function (gradually) after childhood. Orange, which includes Australia and New Zealand and many countries where ancestors have immigrated from many different countries are orange and are a ‘mixture! Nevertheless, this mixture usually ensures that about half the population become lactose intolerant.
Worldwide distribution of the LCT gene function
Lactase persistence = continued enzyme production & lactose digestion in adulthood (GREEN).
Lactase non-persistence = gradual reduction after childhood — the ancestral, default state (RED).
Orange reflects a mixture of the genes but in Australia, about 25% of people lack the enzyme. The incidence is much higher in indigenous people and those from ‘red countries’.
When Does Lactase Production (typically) Decline?
All normal infants produce high lactase naturally so they can digest breast milk. However, there are some rare individuals who lack the lactase gene completely.
In people without lactase persistence alleles, lactase expression begins to decline after weaning — this is primary lactase non-persistence. This usually occurs in early childhood between about ages two and five. However, between the ages of 5 and 10, many show a significant drop in lactase levels while others will be older. Nevertheless, most non-peristant people will have some low lactose activity until they lose the ability completely,
Approximate age trends
There’s no single “magic year,” but research shows general trends:
| Age | Lactase activity direction |
|---|---|
| Birth–weaning (0–2 years) | High lactase production |
| Early childhood (2–5 years) | Begins to decline in non-persistent individuals |
| Around 5–10 years | Many show significant drop in lactase levels |
| Adolescence–adulthood (10–20+ years) | Most non-persistent people have low lactase activity |
- In some populations (e.g., East Asians), lactase activity drops rapidly soon after weaning.
- In Northern Europeans, the decline is slower and many stay relatively tolerant into adulthood even without persistence alleles — because gene expression remains higher longer. There is some growing evidence that exposure to sunlight accelerates the decline.
LACTOSE INTOLERANCE: Once a person’s lactase gene switches off, they can no longer metabolise lactose. The symptom onset (bloating, gas, diarrhoea) depends on how much lactose is eaten and individual gut sensitivity, so people can be low in lactase but not symptomatic until later. Nevertheless, like so many other metabolic functions, stress may greatly exacerbate symptoms and (as in my case) the beginning of a critical exam might be one such trigger!
Worldwide Prevalence — Approximate Country/Region Patterns
Overall 65-75% of the world’s adult population have some degree of lactose maldigestion but the differences between populations suggest that ‘lactose persistance’ evolved multiple times in human history. This seems to have been associated with the introduction of the dairy industry at different times throughout history and its effects on the gene’s evolution.
The Cure is So SIMPLE – COME ON MANUFACTURERS & SUPERMARKETS!
I started by referring to the Dairy section of Supermarkets, where in Australia (at least) there are only a couple of manufacturers who are resourceful enough to remove the Lactose from their dairy products! These lactose-free but otherwise full dairy products taste exactly the same as those with lactose but DON’T UPSET THE GUT. Everyone can happily consume them and greatly reduce their risk of osteoporosis at the same time!
…. and while we are at it, please make all the other small ice-creams lactose free. We will all feel so much better. If those of us who are susceptible can just avoid lactose, we will save hugely on medical bills and should live longer and stronger. For those who aren’t sensitive, it will make no difference!
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Comment: Please read more of my blogs on drjudyford.com and find my books on healthy living and ageing on this link on Amazon.