The prevalence of type 1 diabetes was relatively stable for much of human history until the second half of the 20th century.

But something very strange began to happen around 1950. Suddenly, the rate of type 1 diabetes, especially in children, began to increase sharply. Since then, most countries around the world have seen a linear upturn in T1D cases, a trend that has not slowed over the last decade.

Despite seeing this strange 70-year uptick in cases, researchers are still struggling to figure out exactly why this phenomenon is taking place. Some theories, such as the vaccine and cow’s milk connection, appear less plausible than once thought but there are plenty of others that still appear to have some validity.

In this article, we will take a closer look at this worrisome phenomenon and dissect some of the more likely causes behind it.

How T1D Rates Have Changed Over Time

Multiple studies looking into the prevalence of type 1 near the middle of the last century found that rates doubled from around 1950 to about 1965 in the US. Stranger still, this same surge was seen in many European countries around that same time.

More recent research into the prevalence of T1D shows that this worrisome trend continues in most countries around the globe.

The SEARCH for Diabetes in Youth campaign reported that the prevalence of the disease in people under the age of twenty rose by 21% between 2001 and 2009. Globally, the rate of type 1 appears to be increasing at about 3% per year.

What is most astonishing about this data is how it seems to be consistent across countries while simultaneously appearing to effect some nationalities more than others.

Scandinavian countries, the US, the UK, and Saudi Arabia all have the highest incidence of type 1. Still, despite having a much lower occurrence of the disease, countries like China, India, and Brazil are all seeing similar rates of increase.

This appears to indicate that predisposition to the condition is much more similar across different genotypes than we thought. However, one SEARCH study looking at American youth found that the rate of increase in Hispanics was almost four times the rate of increase in non-Hispanic whites.

It would seem that, while rates of T1D are rising in all populations, we are seeing the fastest rise in populations that have traditionally been less affected.

Why Are Type 1 Diabetes Rates Rising?

There is a clear increase in the occurrence of type 1 in all areas of the world, and the rate of that increase also seems to be growing. 

A number of theories have been put forward over the last few decades to try and explain this phenomenon.

The Hygiene Hypothesis

Over the last century or so, we have learned a lot about pathogens and how infectious diseases are spread. Ironically, it maybe this focus on reducing the spread of these types of illnesses that has led to an increase in T1D.

Recent research has shown a strong correlation between infants growing up with pets and a lower rate of childhood asthma and allergies. Scientists believe this connection has something to do with the increased number of pathogens children living in homes with pets are exposed to early on.

This same process of “immune system priming” may be beneficial in helping reduce the risk of autoimmune diseases such as diabetes. This was a theory first brought forward by David Strachan in 1989 and continues to gain support today.

This theory would explain why rates of diabetes are rising in developed countries where sanitation continues to improve and children are less and less likely to be exposed to viruses and bacteria with each generation. 

Where this theory comes up short is in explaining why T1D rates continue to rise in countries where childhood disease and contact with pathogens is still quite prevalent. 

The Viral Hypothesis 

The viral hypothesis represents, in some way, the antithesis of the hygiene hypothesis. Here, scientists have found a connection between increased exposure to certain viruses and the development of type 1 diabetes.

Research shows that some viruses may trigger or accelerate autoimmune activity in a predisposed person. Rubella, mumps, and rotavirus have all been implicated in this phenomenon, but enterovirus seems to have the most concrete connection in recent studies. 

Long term environmental studies following children with type 1 relatives have found that a large number of those that go on to develop diabetes were infected with enterovirus in the months or years before they tested positive for autoantibodies. There even appears to be some connection between pregnant women getting enterovirus and their child having a higher likelihood of getting type 1. 

While there is a huge amount of evidence linking certain viral infections to the development of type 1, this explanation doesn’t quite explain the sudden rise in T1D prevalence. Especially considering that childhood viral infections have become less common in recent decades.

Breastfeeding and Formula Hypothesis

One other hypothesis that continues to hold up, though the exact mechanisms have changed some, is the association between infant feeding methods and the development of type 1.

There have been some connections drawn between early exposure to cow’s milk, especially dairy-based formula and the prevalence of type 1. But more recent research has focused on what tends to be missing when cows milk is fed early instead of breast milk.

Like the first two hypotheses, this one focuses on the development of the early immune system. 

There are many molecules in breast milk that seem to prevent infection and even autoimmunity in infants. Secretory IgA, for instance, plays an important role in both protecting intestinal flora and providing antibodies against specific threats. Even the insulin present in mother’s milk appears to play some role in reducing the odds of developing type 1.

Unfortunately, this theory alone also falls short of explaining the consistent rate of growth in T1D prevalence. While there was a noticeable drop off in breastfeeding rates in the US around the middle of the 20th century, that rate has recovered somewhat since, while the rate of T1D prevalence continues to grow.

“Balance Shift” Might Be the Answer

As a single explanation for the increasing rates of type 1, none of the theories postulated so far appear to provide an answer. However, if we look at all of the plausible explanations as factors that are interconnected, the possibility of building an explanation that does align with current trends is much more likely.

This “Balance Shift Model” as postulated Francesco Maria Egro, describes how a balance between protective and diabetogenic factors must remain in place in order for the prevalence of the disease to stay consistent. 

For example, the protective power of early exposure to pathogens and the immune-supporting benefits of breastmilk might override the diabetes-inducing power of certain viruses. If a child is not breastfed, then that balance may still be maintained through greater protective qualities of pathogen exposure or through another theory, such as higher vitamin D levels.

But, if multiple protective factors are reduced simultaneously, we would expect the rates of type 1 to rise. Similarly, if deleterious factors were increased, we could also expect rates of T1D to go up.

What these decreasing protective factors and increasing diabetogenic factors may be in any given country is likely to be different. But the results–an increase in T1D prevalence–would be the same.

The beauty of the Balance Shift theory is that it doesn’t discount the many other T1D prevalence theories that do appear to have evidence in their favor. Instead, it validates a wide range of correlations by explaining how each plays a part in determining whether a person who is predisposed to diabetes will get the disease or not.

And more importantly, as an answer to why rates are rising, it explains how we are seeing the same trends in most countries despite vastly different cultural practices and health issues. 

While we still don’t know exactly what all the factors that play into this model might be, the model appears to be the most plausible explanation for the increase we continue to see in T1D diagnosis. 

And for now, this might be the most complete answer we will get.