Chronic Disease: genes vs environment-which matters more?

I thought my parents ate well. Home cooked food made from scratch. Lots of pulses and vegetables. But they both have diabetes, and in the case of my father some pretty bad consequences of the disease including multiple heart attacks from his 50s, visual loss in his 60s and by his 70s complete blindness.

On the other hand I have met people who eat ultra-processed food and desserts daily, yet they aren’t diabetic.

For me, like for most people, this ostensible lack of consistency between a person’s actions and their health outcomes baffled me and made me think that lifestyle changes are hit and miss and genetics is a far more important determinant of health.

But I really didn’t want to become diabetic, so this question of how best to live sat in the back of my mind percolating.

You would think that as a medical doctor I would know a lot about health. And you would be right. But in fact whilst our medical training taught us the language and the landscape of human physiology and the tools we currently work with to manage disease, it didn’t really teach us about the upstream determinants of health — in essence, how to head off disease altogether, or even the power to reverse it -particularly in its early stages.

In fact we don’t even hope for that in conventional medicine. I had to go back to the science for this.

Hearteningly, the science is there, and it resoundingly comes up with the same answers again and again.

How much do our genes matter?

Bear in mind that most people in families not only share genes, but also their environment including lifestyle habits -such as what they eat and how much they exercise.

But what if you looked at identical twins who have exactly the same genes who grew up differently, and teased out how much of their risk of disease is down to their genes, and how much is down to their lifestyles?

Well, that’s a pretty popular area of genetics, and we now know that only 10–20% of disease is down to our genes.

That means a whopping 80–90% of our risk of illness is down to how we live. In my view this is enormously heartening — we can take control of our health destiny!

It’s not what you have, it’s the way that you use it

At the time I was doing my PhD in genetics, a very exciting endeavour called the ‘Human Genome Project’ was taking place at centres around the world.

We were working out the manual of how to make every component of a human being by reading and charting the entire human genetic code. There were high hopes that we would discover that many diseases were due to a defect in a gene that we hadn’t known about before. What is more, once we had this information we could administer working copies of the gene (gene therapy) and help improve outcomes for patients.

But that is not what happened.

If I were to tell you that a mouse has 30 000 genes, a chicken has 22 000 genes, a fruit fly has roughly 14 000 genes and that the rice plant has 51 000 genes you might start to notice that the number of genes doesn’t seem to correlate as we might predict with the complexity of the species.

So what would you estimate from these numbers about the number of genes needed to make all the components of a human? It turns out, we have approximately 30 000 genes — roughly the same as a mouse!

Each of these genes can potentially make several proteins. The way it works is like this: imagine one gene is called ‘SPECIES’. From ‘SPECIES’ we have the letters (or code), to make the words (or proteins) ‘SPIES’, ‘PIECE’ and ‘SPECIES’.

The more interesting finding is that whilst the code itself doesn’t change easily, how available a section of code is does change. In fact, a whole range of factors can change how available a section of our code is including what we eat, when we eat, how much we exercise, how stressed we are and even how often we experience periods of uncomfortable heat or cold.

These outside factors trigger sections of our genetic code to either hide from — or show themselves to — the machinery in our cells that then make the component it codes for.

So for example, if I eat a lot of junk food daily, this may signal my body to start hiding the code ‘PIECE’ from the gene ‘SPECIES’, that we mentioned in the previous paragraph, from the factory floor so it cannot be made. Now, if ‘PIECE’ codes the instructions to make a really important quality control protein that checks that DNA has been copied properly whenever a cell divides, then it’s a bad idea for it to become invisible.

This whole field is called Epigenetics. It is how we adapt to changes in our environment. We now know that positive lifestyle changes can switch off cancer promoting genes, reduce inflammation, improve our mental wellbeing and even slow ageing — and that these changes can happen in a matter of mere weeks!

Lifestyle vs Drugs

It is so much easier to simply take a tablet than to change the way we live, and we have a lot of faith in the effectiveness of pharmaceuticals. No doubt they are frequently lifesaving and have a vital role in many scenarios.

But, apart from a few, they are blunt tools at altering the course of lifestyle related diseases. They don’t deal with the underlying causes, so they at best slow down the inevitable. To paraphrase Drs Hymen, Ornish and Roisen, the way we currently practice medicine is like mopping the floor below an overflowing basin; what we really need to do is switch off the tap. That is what Lifestyle Medicine does.

A Fantastic Finish in Finland

In 1972, North Karelia in Finland had the highest rate of death from heart disease in the entire world. The government recognised that the main drivers of heart disease were dietary changes following the Second World War and high smoking rates in the region. Increasing affluence had brought an increase in dairy products into the region and these were greatly valued, resulting in high intakes of milk, cream, butter and cheese. The region had the highest cholesterol levels in the country!

An enormous public health initiative was commenced, with a reduction in high fat animal products and smoking as its key messages. By 2012, smoking rates had fallen from 51% to 36%, and cholesterol levels by 20% thanks to dietary changes, with only a small proportion of this due to statin use (these are drugs we use to lower cholesterol). Average blood pressure fell by 15mmHg in men, and by 24mmHg in women — levels you would expect from taking drugs, but without the side effects.

This incredible lifestyle initiative in the region saw death from heart disease fall by a staggering 84% in North Karelia. It is interesting to note that the widespread use of statins (which is consistently amongst the most commonly prescribed drugs in the UK) has not seen such a precipitous fall in cardiovascular mortality, which remains the leading cause of death in the Western world.

‘Little and Often’ — Is It Even Worth It?

One study looked at what happened when a group of 101 men with angina were split into two groups after a routine angiogram (a test to check how narrow the blood vessels supplying the heart are).

Each man had at least one blood vessel that was narrowed by at least 75%.

The first group had standard care whereby a stent was placed in the narrowed blood vessels to open it up again.

The second group were asked to simply use an exercise bike for 20minutes each day.

After 1 year, the exercise group were 26% less likely to have any cardiac event needing hospitalisation than the group who had the procedure to improve blood supply to their heart.

In other words, a mere 20 minutes a day of gentle exercise in people who had quite bad hearts was more effective than opening up those clogged up blood vessels.

Incredible.

So, what about my parents? Did I find the answer to why they became diabetic despite a good diet? I think I have. Read my articles on ‘Why do SO many South Asians get Diabetes?’ to find out why.