Dogs trained to sniff out abnormal blood sugar can be the best friends of diabetes sufferers, research has shown.
A study found that "glycaemia alert dogs" trained by a charity detected early signs of low blood sugar with uncanny accuracy.
To some extent they also responded when their owners' blood sugar levels were too high.
Alerting behaviours included licking, pawing, jumping, staring, vocalising and even fetching a blood testing kit.
Previous reports have described anecdotal cases of dogs reacting when their diabetic owners are at risk of a hypoglycaemic episode or "hypo" - a dangerous drop in blood sugar.
The study aimed to carry out the first assessment of whether specially trained dogs could be used as an early warning system for diabetics.
Scientists studied 17 dogs trained by the charity Medical Detection Dogs to alert owners when their blood sugar was straying out of its target range.
Blood tests for eight out of 10 owners able to provide adequate records showed that the dogs' alarm signals were likely to coincide with abnormal sugar levels.
The dogs performed better than they would have been expected to by chance.
Since obtaining their dogs, all 17 owners - whose ages ranged from five to 66 - reported positive effects, including fewer emergency call-outs, reduced numbers of unconscious episodes and improved independence.
Study leader Dr Nicola Rooney, from the University of Bristol, said: "Despite considerable resources having been invested in developing electronic systems to facilitate tightened glycaemic control, current equipment has numerous limitations.
"These findings are important as they show the value of trained dogs and demonstrate that glycaemia alert dogs placed with clients living with diabetes afford significant improvements to owner well-being, including increased glycaemic control, client independence and quality of life and potentially could reduce the costs of long-term health care."
How dogs detect abnormal blood sugar in their owners is unclear, but scientists suspect they "smell" changes in their breath or sweat.
"While it is believed that dogs use their acute sense of smell to detect changes in the chemical composition of their owner's sweat or breath to respond to glycaemic control, further research is now needed to further understand how dogs carry out this amazing task," Dr Rooney added.
The findings are published in the online journal Public Library of Science ONE.
All but one of the dog-owners in the study had type 1 diabetes, an auto-immune condition that requires daily injections of insulin.
Diabetes affects around 2.6 million people in the UK, about 10% of whom have type 1 disease.
Type 2 diabetes, the more common form, usually occurs later in life when the body ceases to respond properly to insulin and is linked to lifestyle.
Sudden falls in blood sugar often affect people with insulin-dependent type 1 diabetes and can be life-threatening.
Unawareness of the warning signs of low blood sugar has been reported in a quarter of type 1 diabetes sufferers, raising their risk of severe hypoglycaemic epidodes up to seven times.
The dogs in the study consisted of a range of breeds and crosses, including six labradors, a golden retriever, a collie cross, a cocker spaniel and a Yorkshire terrier.