Is Crohn's or colitis genetic? 

Clearing up the confusion

When someone is diagnosed with Crohn's disease or ulcerative colitis, some of the questions people ask me is: "Is it genetic? Will my children get it too?" These are valid questions, but the answers are more nuanced than you might think.

Genes: One piece of the puzzle

Let’s start with what science tells us. Yes, genes play a role in IBD (Inflammatory Bowel Disease), but it’s only part of the picture. Having a family member with IBD does increase your risk slightly, but it’s far from a guarantee.

Here are the real numbers:

Around 10 to 15 percent of people with Crohn's or colitis have a close relative (parent, sibling, or child) with the condition.

If one parent has IBD, a child’s risk is about 5 to 10 percent.

If both parents have IBD, that risk rises to around 30 percent.

But the majority of people with IBD do not have a family history of it.

So, while genetics can open the door, something else usually needs to push it open.

What does “heritability” actually mean?

Sometimes you hear that Crohn's has a heritability of 75 percent, and ulcerative colitis around 67 percent. That sounds high – but it's often misunderstood.

Heritability doesn't mean personal risk. It means that in large population studies, about 75 percent of the variation in Crohn’s cases can be attributed to genetic differences. That’s not the same as saying you have a 75 percent chance of getting it if your parent does.

Twin studies help us understand this better:

Identical twins (who share 100 percent of their genes) have a 30–35 percent chance of both having Crohn’s.

For ulcerative colitis, it’s even lower – around 15–20 percent.

This shows us that even with the same genes, other factors have to be present for the disease to develop.

What else contributes to IBD?

Environmental and lifestyle factors play a huge role. Here are some of the best-supported contributors:

Western-style diet: low fibre, high sugar, processed foods

Antibiotic use, especially in childhood

Changes to the gut microbiome (your internal ecosystem)

Smoking (increases risk of Crohn’s; oddly, may reduce the risk of colitis)

Stress and modern living

Pollution and urbanisation

It’s the combination of genes and environment that seems to trigger the disease in those who are susceptible.

The Ashkenazi Jewish connection

I’ve had clients say things like, “I have Crohn’s because I’m Jewish.” It’s a very understandable concern, and it is true that people of Ashkenazi Jewish descent (from Eastern Europe) have a higher risk of developing Crohn's disease. Studies suggest they are two to four times more likely to develop it compared to others of European ancestry.

To put that into perspective: if about 1 in 100 people in the general population develops Crohn’s, in Ashkenazi Jewish populations it might be closer to 1 in 50 or even 1 in 25. Still uncommon, but more frequent than average.

Why? It seems to be due to specific gene variants like NOD2, which are more common in this group. But even here, it’s important to remember: not everyone with the genes develops the disease, and not everyone with the disease has those genes.

Most importantly, I want people to know that genes are not destiny. Thinking that IBD is “just genetic” can make people feel powerless. In reality, so many other factors influence whether or not someone gets sick, and many of those are things we can do something about.

 What about the Black Plague theory causing colitis and Crohn’s?

There’s an internet myth that says surviving genes from the Black Plague might be responsible for Crohn’s. While it’s true that historical diseases can shape the immune system over generations, there’s no solid evidence linking plague resistance to Crohn’s disease. It remains an interesting theory, but not one to take too seriously just yet.

Should you worry about your children getting IBD?

It’s natural to worry, but try to keep it in perspective:

Most children of people with IBD do not go on to develop it.

Many people who develop Crohn's or colitis have no known risk genes or family history.

What you can do is focus on what supports gut health and immune balance from early on:

• A varied, whole-food, high plant diet such as the Mediterranean diet
• Minimising unnecessary antibiotics
• Supporting the microbiome (e.g. fermented foods, fibre)
• Managing stress
• Encouraging physical activity and time outdoors

Final thoughts: More than just genes

IBD isn’t a simple genetic condition. It’s a complex interplay of genes, environment, lifestyle and gut health. The rapid rise of IBD in countries that are westernising their diets and lifestyles shows that it’s not just about what we inherit, but how we live.

So yes, genetics matter. But they are only one chapter in the story – not the whole book.

And the good news? There are many things you can do to support your gut and immune health, whatever your genes may say.

Join me to restore maximum health to your digestive system!