Many argue that diabetes is the public health crisis of our time and as the national clinical director for obesity and diabetes at NHS England, I am inclined to agree.

Between six and seven per cent of the population have been diagnosed with the condition, which costs the NHS £10 billion annually - equivalent to 10 per cent of its budget. As diabetes rates soar, it is imperative that we tackle this issue.

I qualified 25 years ago and have spent most of my career as a consultant diabetologist at St Mary's Hospital, part of Imperial College Healthcare NHS Trust in west London.

My national role involves three different hats. One for type 1 diabetes, which is nothing to do with obesity; one for type 2 diabetes, which has a lot to do with obesity; and one for obesity itself.

Diabetes is a disease of metabolism. Every cell in our body generates energy to survive. This requires oxygen and food, much of which is broken down into glucose. Blood delivers oxygen and glucose to the cells with the help of a hormone called insulin. Without insulin, cells will starve to death.

The numbers

2.7m - The number of people in England who suffer from diabetes, representing between six and seven per cent of the population
91% - The percentage of sufferers who have type 2 diabetes, which is related to obsesity
0.5m - The number of undiagnosed cases of type 2 diabetes among people in England
60% - The percentage of English adults who are now considered overweight or obese
80% - The percentage of type 2 diabetes cases that relate to lifestyle factors such as weight, diet and exercise, and as such could be prevented

The pancreas senses when blood sugar levels rise after eating and produces just the right amount of insulin.

This process works very efficiently - unless you have diabetes.

There are broadly two different types of diabetes with major differences in cause.

In type 1 diabetes the immune system destroys the cells in the pancreas responsible for insulin production. Without insulin injections, people with this condition cannot survive.

Insulin was first discovered, isolated and purified in 1922. Before then, there was a 100 per cent death rate for type 1 diabetes.

In type 2 diabetes, the problem is not deficiency, but resistance to the action of insulin.

The pancreas responds by producing more insulin. It does that successfully for years, but eventually gets tired and production then falls so glucose levels rise.

As people gain weight, they become more resistant to the action of insulin. As more of us become overweight and obese, so the number of people developing type 2 diabetes is increasing.

While the causes are different, the consequences of types 1 and 2 are very similar. Glucose generates osmotic forces, which means it draws in water. High sugar causes high volumes of urine, which leads to dehydration and feeling thirsty. Alarm bells for type 1 diabetes ring if there is dramatic weight loss too.

The osmotic effect also occurs in eyes - in the lens, making it harder to focus. Once treatment commences, these osmotic symptoms will disappear.

Unfortunately people with types 1 and 2 diabetes are both susceptible to long-term complications.

The risk of heart attack and stroke doubles if you have diabetes and the condition is one of the main causes of blindness and kidney failure in England.

Nerves in the feet can also be affected which, in certain situations, can lead to amputation.

Human insulin has been manufactured since the 1980s. It is produced in many forms and can be a mixture of quick and long-acting. Nevertheless, we are unable to match exactly insulin delivery to the body's requirements.

When you get a mismatch, bad things happen. Insufficient insulin leads sugars to rise, triggering osmotic symptoms.

Too much insulin causes hypoglycaemia. You sweat, your heart races, you shake and can feel very anxious. In extreme cases people lose consciousness and can even die.

Fortunately however, most people get very early warning signs of hypoglycaemia and can take appropriate action.

In England, 2.7 million people have diabetes. Of those, 91 per cent are type 2 and 9 per cent type 1.

But for every five diagnosed cases of type 2 diabetes, there is one undiagnosed, meaning a further half a million people are unaware that they have the condition.

More than six in 10 English adults are now overweight or obese, and as the obesity crisis mounts, so does the prevalence of diabetes. Genetic factors also increase the risk, but only by a small amount.

That said, there is a huge ethnic dimension to the condition. Diabetes is particularly prevalent within the South Asian and African and Caribbean communities, though we don't know whether the cause of the excess is genetic or environmental.

Being Jewish does not put you at higher risk than the wider population - which is still too high.

If we continue running the health service in the way we are now, the NHS in England will see a shortfall of
£30 billion by 2020.

Last October NHS England published The Five Year Forward View, which sets out how we can meet
£22 billion of that shortfall through different ways of working, including looking at how to prevent diseases like diabetes.

Unfortunately we cannot prevent type 1, but as weight is an important predictor of type 2 we can certainly make a difference there.

People with a normal body mass index (BMI) can develop type 2, yet being overweight significantly increases the likelihood.

Research suggests that up to 80 per cent of type 2 diabetes relates to lifestyle factors, much of which could therefore be prevented by adopting lifestyle changes, such as losing weight, improving diet and exercising.

Will that protect you for ever? Maybe not, but it can delay the onset by a number of years. That delay reduces blindness rates, heart attacks, strokes and ultimately deaths.

So prevention is essential, as it gives people more years lived in health and less exposed to the awful complications of diabetes.

Professor Jonathan Valabhji is NHS England's national clinical director for obesity and diabetes. This is a version of his lecture given at last week's Jewish Care Health Insights session.

The next in the series of Health Insight events, hosted by Jewish Care in partnership with the JC, will be held on October 8, when Professor Tony Rudd, the national clinical director for stroke, NHS England, will give a talk entitled "Strokes: A Treatable Disease We Need to Treat Better". For more information about the Health Insights events go to www.jewishcare.org/health-insight-evenings, or call 0208 922 2837.