People who have type 1 diabetes require insulin injections to manage blood sugar levels. A trained dog may be able to detect when their blood sugar levels are falling to potentially dangerous levels.

"Magic is incredible - he is not just a wonderful companion, but he is my 'nose' to warn me if I am at risk of a hypo," said Claire Pesterfield, a type 1 diabetes patient from Cambridge University in the UK, referring to her dog.

"If he smells a hypo coming, he will jump up and put his paws on my shoulders to let me know," said Pesterfield.

Hypoglycaemia - low blood sugar - can cause problems such as shakiness, disorientation and fatigue,  researchers said.

If the patient does not receive a sugar boost in time, it can cause seizures and lead to unconsciousness. In some people with diabetes, these episodes can occur suddenly with little warning, they said.

Researchers believed that certain naturally-occurring chemicals in exhaled breath might change when glucose levels were low.

In a preliminary study to test this hypothesis, scientists gradually lowered blood sugar levels under controlled conditions in eight women, all around their forties, and all with type 1 diabetes.

They then used mass spectrometry - which look for chemical signatures - to detect the presence of these chemicals.

Researchers found that levels of the chemical isoprene rose significantly at hypoglycaemia - in some cases almost doubling.

They believe that dogs may be sensitive to the presence of isoprene, and suggest that it may be possible to develop new detectors that can identify elevated levels of isoprene in patients at risk.

"Isoprene is one of the commonest natural chemicals that we find in human breath, but we know surprisingly little about where it comes from," said Mark Evans from Cambridge University.

"We suspect it is a by-product of the production of cholesterol, but it is not clear why levels of the chemical rise when patients get very low blood sugar," said Evans.

"Humans are not sensitive to the presence of isoprene, but dogs with their incredible sense of smell, find it easy to identify and can be trained to alert their owners about dangerously low blood sugar levels," he added.

The findings were published in the journal Diabetes Care.

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