It's estimated that at least 2.4 million Britons have diabetes, but only 1.4 million of them know it yet. The rest make up the "lost million" Britons who haven't yet been diagnosed. This extract from Diabetes for Dummies by Dr Sarah Jarvis and Alan L Rubin (Wiley, £14.99) identifies the symptoms of both types of diabetes

How do doctors define diabetes?
The standard definition of diabetes mellitus is excessive glucose in a blood sample and in other words, you have too much sugar in your blood. For years, doctors set this level fairly high. The World Health Organisation (WHO) lowered the standard level for normal glucose in 1997, and now almost everyone in the UK uses this new standard for diagnosis. Why did the WHO decide to lower the standard level? Because too many people were experiencing complications of diabetes even though their glucose level wasn't high enough to be diagnosed with diabetes. The new definition of diabetes includes symptoms of diabetes, along with any one of the following three criteria:

A random plasma sugar level greater than 11 mmol/l (millimoles per litre)

A fasting plasma sugar level greater than or equal to 7mmol/l (or 6.1mmol/l in whole blood)

A plasma sugar level greater than 11 mmol/l two hours after drinking 75 grams of glucose dissolved in water in an oral glucose tolerance test (OGTT)

Mmol/l stands for millimoles per litre. This way of measuring blood glucose concentrations is used almost all over the world, except in America. Over there, most glucose measurements are in mg/dl, or milligrams per decilitre. To translate mmol/l into mg/dl, multiply your figure in mmol/l by 18. So if you're travelling in the US and need to speak to a doctor, make sure that one of you has a calculator to hand!

What type of diabetes do you have?

Identifying the symptoms of type 1 diabetes
Type 1 diabetes used to be called juvenile diabetes because it occurs most frequently in children. However, so many cases are found in adults that doctors don't use the term juvenile any more. The disease isn't gender biased, either. Males and females get type 1 diabetes to an equal degree. The following sections list the general symptoms and give some important information on how and when these symptoms can manifest themselves in kids.

General symptoms
Before your doctor actually diagnoses you with type 1 diabetes, you may notice that you have some of the major signs and symptoms.

See your doctor
If you (or your child) experience the following symptoms, take time to ask your doctor about the possibility that you have diabetes:

Frequent urination: You experience frequent urination because your kidneys can?t return all the glucose to your bloodstream when your blood glucose level is greater than about 10 mmol/l. The large amount of glucose in your urine makes the urine so concentrated that water is drawn out of the blood and into the urine to reduce the concentration of glucose in the urine. This fills up the bladder repeatedly.

Increased thirst: Your thirst increases because you lose so much water in your frequent urination that your body begins to dehydrate.

Weight loss: You lose weight as your body loses glucose in the urine and your body breaks down muscle and fat looking for energy.

Increased hunger: You notice that you're increasingly hungry. Your body has plenty of extra glucose in the blood, but your hunger is a result of your cells becoming malnourished because you lack insulin required to allow the glucose to enter your cells. Your body is going through "hunger in the midst of plenty".

Weakness: You feel weak because your muscle cells and other tissues don't get the energy that they require from glucose.

Identifying the symptoms of type 2 diabetes
We're pretty convinced that at least 2.4 million Britons have diabetes, but only 1.4 million of them know it yet. The rest make up the "lost million" Britons who haven't yet been diagnosed.

See your doctor
The following signs and symptoms are good indicators that you have type 2 diabetes. If you experience many of these symptoms, check with your doctor:

Fatigue: Type 2 diabetes makes you tired because your body's cells aren't getting the glucose fuel that they need. Even though there is plenty of insulin, your body is resistant to its actions.

Frequent urination and thirst: You find yourself urinating more frequently than usual, which dehydrates your body and leaves you thirsty.

Blurred vision: The lenses of your eyes swell and shrink as your blood glucose levels rise and fall. Your vision blurs because your eye can't adjust quickly enough to these changes in the lens.

Slow healing of skin, gum and urinary infections: Your white blood cells, which help with healing and defend your body against infections, don't function correctly in the high-glucose environment present in your body when it has diabetes. Unfortunately, the bugs that cause infections thrive in the same high-glucose environment. So diabetes leaves your body especially susceptible to infections.

Genital itching: Yeast infections, often called thrush, also love a high-glucose environment. So diabetes is often accompanied by the itching, creamy white vaginal discharge and discomfort of yeast infections.

Numbness in the feet or legs: You experience numbness because of a common long-term complication of diabetes, called neuropathy. If you notice numbness and neuropathy along with the other symptoms of diabetes, you probably have had the disease for quite a while, because neuropathy takes more than five years to develop in a diabetic environment.

Heart disease: Heart disease occurs much more often in people with type 2 diabetes than in people who don't have diabetes. But the heart disease may appear when you are merely glucose-intolerant, before you actually have diagnosable diabetes.

Obesity: If you're obese, you are considerably more likely to acquire diabetes than you would be if you maintained your ideal weight. But not all obese people develop diabetes, so obesity isn't a definite sign that you have diabetes.

Extracted with permission from Diabetes for Dummies by Dr Sarah Jarvis and Alan L Rubin (John Wiley & Sons Inc., £14.99)