Type 2 diabetes is a complex condition and your chances of developing it depend on a mix of different risk factors. Unfortunately, misunderstandings about what drives type 2 diabetes are all too common.
Type 2 diabetes develops when the insulin your pancreas makes doesn’t work properly, or your pancreas can’t make enough insulin to meet your body’s needs. While scientists are still unravelling the precise reasons behind this, decades of research have uncovered a variety of factors which can increase someone’s risk of developing type 2.
Often, a lack of knowledge about type 2 diabetes can lead to misunderstandings about its causes. For most people, no single factor explains why they develop the condition. Instead, think of your risk like a recipe, with various ingredients combining to create a unique result. Each person's risk profile is like a custom blend—some ingredients, such as genetics or age, are fixed, while others, like diet and activity level, can be adjusted. Here’s a snapshot of what research has revealed.
Genetics
Type 2 diabetes has a strong genetic basis. Scientists have identified at least 550 different genes that are linked to the condition. Some versions (variants) of these genes can increase risk of type 2 and others can reduce risk. It is the combination of all these gene variants that will either give you a higher or lower likelihood of developing type 2.
Different genes influence risk in different ways depending on what biological processes they provide instructions for. For example, some genes variants will instruct the body to store internal fat in the liver and pancreas, which can prevent insulin-making beta cells from working properly. Other gene variants impact how well the body responds to insulin, make beta cells more vulnerable to damage, or influence hormones that are involved in blood sugar control.
While your genetic make-up can make you more susceptible to developing type 2 diabetes, your genes are not your destiny. Some people who have a high genetic risk of type 2 will not go on to develop the condition because other factors, such as their diet and physical activity levels, help counteract the effects of their genes. And it’s possible for people with a low genetic risk to develop type 2 when there are other risk factors at play.
Bodyweight and body fat
People living with overweight or obesity are more at risk of type 2 diabetes. But around 15% of people living with type 2 diabetes have a Body Mass Index (BMI) that’s not in the obesity or overweight category.
Our research has shown that where the body stores fat, and not just overall weight, is important when it comes to type 2 risk. And that this is influenced by our genetics.
Carrying extra weight around your middle and having a high waist measurement can lead to fat building up in and around organs, such as the liver and pancreas, affecting how they work and increasing the likelihood of type 2 diabetes.
Meanwhile, the tendency to store fat under the skin rather than in organs, lowers the risk of type 2.
Diet
Our diet affects our bodyweight, insulin sensitivity, and levels of inflammation. These factors, in turn, can contribute to the risk of developing type 2 diabetes.
How many calories you consume overall will impact on your risk. Regularly consuming an excess of calories can lead to weight gain, and living with overweight or obesity is a well-established risk factor for type 2 diabetes.
Certain food groups have been linked to risk of type 2 diabetes. However, it's the combination of foods and drinks in your diet that will have the most impact on your health, rather than single foods or nutrients. Overall, a dietary pattern that is higher in fruit and vegetables, foods rich in fibre, and whole grains, and lower in red and processed meats, foods high in saturated fat, refined grains and sugar-sweetened drinks has the strongest evidence for reducing risk of developing type 2 diabetes.
For other foods, nutrients or diets, evidence is weaker, making it difficult to draw clear conclusions about the impact on type 2 diabetes risk.
Ethnicity
People from Black African, African Caribbean and South Asian (Indian, Pakistani, Bangladeshi) backgrounds are at a higher risk of developing type 2 diabetes at a younger age and at lower bodyweights compared to those from a White European background.
There may be biological reasons that contribute to this. For example, people from South Asian backgrounds are more likely to develop insulin resistance at a younger age. This could be linked to how fat is stored in the body, particularly around the middle, increasing the risk of fat building up around the liver and pancreas.
Beyond biological reasons, a mix of social and cultural factors – along with a lack of culturally appropriate information and support for people with, or a risk of, type 2 from different ethnic backgrounds - all play a part in explaining the greater risk for some ethnic groups.
Age
The risk of type 2 diabetes increases with age. You’re more at risk if you’re White and over 40, or over 25 from an African-Caribbean, Black African, Chinese or South Asian background.
The biological changes that happen as we age can affect how well the body responds to insulin and the health of insulin-making beta cells.
Birthweight
Being born small has been linked with a greater risk of developing type 2 diabetes later in life. This is thought to be because low birth weight often leads to rapid “catch-up” growth, and this may predispose people to type 2 as an adult.
Some studies also suggest that babies with low birth weight are more likely to inherit a gene that can increase their risk of type 2.
Other health conditions
Having certain health conditions is associated with an increased risk of developing type 2 diabetes. One example is gestational diabetes, a form of diabetes that can develop during pregnancy. Women who’ve had gestational diabetes have about a 10-fold increased risk of developing type 2 diabetes in later life.
Other conditions with strong links to type 2 include polycystic ovary syndrome (PCOS) and metabolic dysfunction-associated steatotic liver disease (MASLD). PCOS affects the ovaries and is linked to insulin resistance. Research has suggested that more than half of women with PCOS develop type 2 diabetes by age 40. While MASLD can also increase the risk of type 2 more than two-fold.
Having a history of high blood pressure, heart attack or strokes can also cause damage that may increase the risk of type 2 diabetes.
And it’s not just our physical health. Stress, loneliness and certain mental health conditions including depression, schizophrenia and bipolar disorder, have also been linked with a greater risk of developing type 2.
Sleep
Disturbed sleep, including not getting enough sleep or trouble falling or staying asleep, has been associated with an increased risk of type 2 – as have sleep disorders, like insomnia and sleep apnoea.
Sleep disturbances and disorders have been linked to insulin resistance and changes in other hormones, which affect how our body processes glucose.
Gut microbiome
Microbes living in our gut, including bacteria and fungi, are collectively known as the gut microbiome. These can affect our health and there are clues they could have a hand in the development of insulin resistance and type 2 diabetes.
There’s evidence that people with type 2 diabetes often have a different balance of microbes in their gut compared to people without diabetes. One large study identified certain species of microbes linked with type 2 that could change how the body turns sugar into energy. Other research suggests that the microbiome can influence levels of inflammation inside the body – a factor that has been linked to insulin resistance.
But we still don’t know if differences in the gut microbiome are a cause or consequence of type 2 diabetes. Work continues to better understand the role of the gut microbiome in the development of type 2 diabetes, and whether interventions to change the gut microbiome could be a way to reduce type 2 risk.
Physical activity
Being physically active can help to manage bodyweight. It also increases the amount of sugar used by muscles and helps the body to use insulin more effectively. Not doing enough activity can therefore increase the risk of type 2 diabetes.
And it’s not just about exercising. Spending long periods sitting or lying down, known as being sedentary, is also linked with type 2 diabetes – even if you do the recommended amount of exercise per week.
Income levels
In the UK, people living in more deprived areas are significantly more likely to have type 2 diabetes.
Deprivation doesn’t directly cause a greater risk of type 2, but people living in deprived communities are more likely to experience conditions that put them at increased risk of type 2. For example, they are more likely to live with obesity, have lower levels of physical activity, smoke and eat fewer fruit and vegetables, compared to those from the least deprived communities, driven by having less access to good healthcare, green spaces and affordable, healthy foods.
Pollution
Evidence is building to suggest that the quality of the air we breathe influences our risk type 2 diabetes. Pollution carries fine particles, including metals and other toxins. It’s thought these can trigger insulin resistance and inflammation, which prevents the body from removing glucose in the blood and turning it into energy.
One large study has estimated that as many as 1 in 10 new cases of type 2 in the UK could potentially be linked to air pollution.
Emerging research also suggests that road traffic noise and light pollution in urban areas could also disrupt how our body turns glucose into energy, increasing the risk of developing type 2.
This is a relatively new area of exploration but given the number of people living in heavily polluted areas, efforts to reduce pollution could be an important new strategy to help prevent cases of type 2.
Confronting stigma
No one thing causes type 2 diabetes and the reasons someone develops it will be individual to them. Misunderstandings and assumptions about the causes of type 2 diabetes fuel diabetes stigma. Increasing understanding of the complex and multiple drivers of type 2 diabetes is a crucial step in addressing the root cause of stigma, and reducing the harm and discrimination that come with it.
We’re committed to funding research to uncover more about the causes of type 2 diabetes as well as ways to address diabetes stigma.
