If you have coeliac disease, it is crucial you do not eat any gluten. If you have untreated or undiagnosed coeliac disease and are still eating gluten, several complications can occur.

It is a common misconception that eating a little gluten will not harm you. Eating even tiny amounts can trigger symptoms of coeliac disease and increase your risk of developing the complications outlined below.

Malabsorption

Malabsorption (where your body does not fully absorb nutrients) can lead to a deficiency of certain vitamins and minerals. This can lead to certain conditions, including:

• iron deficiency anaemia
• vitamin B12 and folate deficiency anaemia
• osteoporosis – this causes your bones to become brittle and weak

Click on the links above for more information on the symptoms and treatment of these conditions.

Malnutrition

As coeliac disease causes your digestive system to work less effectively, severe cases can sometimes lead to a critical lack of nutrients in your body. This is known as malnutrition, and can mean your body is unable to function normally or recover from wounds and infections.

If you have severe malnutrition, you may become fatigued, dizzy and confused. Your muscles may begin to waste away and you may find it difficult to keep warm. In children, malnutrition can cause stunted growth and delayed development.

Treatment for malnutrition usually involves increasing the number of calories in your diet and taking supplements.

Read more about the treatment of malnutrition.

Lactose intolerance

If you have coeliac disease, you are more likely to also develop lactose intolerance, where your body lacks the enzyme to digest the milk sugar (lactose) found in dairy products. Lactose intolerance causes symptoms such as bloating, diarrhoea and abdominal discomfort.

Unlike gluten in coeliac disease, lactose intolerance does not damage your body. Rather, you may get some gastrointestinal symptoms when you take foods containing lactose as you can't digest it properly.

Lactose intolerance can be effectively treated by not eating and drinking dairy products that contain lactose. You may also need to take calcium supplements – as dairy products are an important source of calcium, you will need to compensate for not eating them.

Read more about the treatment of lactose intolerance.

Cancer

Some research has suggested having coeliac disease can increase your risk of developing certain types of cancer, including bowel cancer and lymphoma (cancer of the lymphatic system, which is part of the immune system).

The same research found people with coeliac disease have a lower risk of developing lung and breast cancer, although the reasons for this are unclear.

It is estimated people with coeliac disease are twice as likely to develop bowel cancer than the general population.

However, this is still a very small increase in risk – only 1 in every 200 people with coeliac disease will develop bowel cancer in the first 10 years after diagnosis.

As age is an independent risk factor for bowel cancer, your risk of developing bowel cancer increases as you get older, in line with the general population.

The risk of developing cancer is thought to be highest during the first year after diagnosis, before dropping to normal as your gluten-free diet starts to take effect.

Whether or not you have coeliac disease, it is important to be aware of the symptoms of bowel cancer, which include:

• blood in stools (faeces)
• unexplained weight loss 
• changes in your normal bowel habit that last more than four weeks 

See your GP if you develop these symptoms.