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

It's 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 complications.

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

• iron deficiency anaemia
• vitamin B12 or folate deficiency anaemia
• osteoporosis – a condition where your bones become brittle and weak

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 result in your body being unable to function normally or recover from wounds and infections.

If you have severe malnutrition, you may become fatigued, dizzy and confused. In children, malnutrition can cause stunted growth and delayed development.

Treatment for malnutrition can involve increasing the number of calories in your diet and taking supplements.

Find out more about treating malnutrition.

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

Unlike gluten in coeliac disease, lactose does not damage your body. But you may get some gut-related symptoms when you eat foods containing lactose because you can't digest it properly.

Lactose intolerance usually gets better once you change to a gluten-free diet and your gut has recovered. Until it gets better, it can be effectively treated by not eating or drinking dairy products that contain lactose. You may also need to take calcium supplements – dairy products are an important source of calcium, so you'll need to compensate for not eating them.

Cancer is a very rare but serious complication of coeliac disease.

Someone with coeliac disease has a slightly increased risk of developing certain cancers. Recent research shows that this increased risk is less than previously thought.

Cancers associated with coeliac disease include small bowel cancer, small bowel lymphoma and Hodgkin lymphoma. However, most people with coeliac disease will not develop any of these.

Once you've been following a gluten-free diet for some time, your risk of developing these types of cancer is the same as that of the general population.

Poorly controlled coeliac disease in pregnancy can increase the risk of developing pregnancy-related complications, such as giving birth to a baby with a low birth weight.

Coeliac UK has more information and advice about coeliac disease and pregnancy.

You can also read more about a healthy diet in pregnancy.