People with diabetes who smoke have again been urged to kick the habit after scientists discovered that nicotine can cause persistently raised blood sugar levels.
It is well known that smoking is linked to serious complications for diabetes sufferers, but experts were unable to identify what tobacco substance was to blame.
In new research carried out in California, scientists found that nicotine concentrations typical of those in smokers appeared to raise long-term blood sugar levels in diabetics.
Almost three million people in the UK are diagnosed with diabetes, and close to a million more may have the condition without knowing it.
Complications of the disease include potentially life-threatening heart attacks, strokes, kidney failure and nerve damage.
They tend to result from blood sugar levels running out of control and wreaking destruction in the body. The key to preventing complications is good management of blood sugar.
The new research, reported at the meeting of the American Chemical Society in Anaheim points to the prime suspect being nicotine.
The tests were carried out by measuring levels of a marker blood protein called haemoglobin A1c (HbA1c), the gold standard method of monitoring long-term blood sugar in people with the disease.
"Nicotine caused levels of HbA1c to rise by as much as 34%," said Dr Xiao-Chuan Liu, from California State Polytechnic University in Pomona, who led the study. "No one knew this before. The higher the nicotine levels, the more HbA1c is produced."
He said the benefits of quitting probably meant people with diabetes should not avoid using nicotine patches and similar products for short periods of time. However, the research raised concerns about the long-term use of nicotine replacement therapy.
"Good article. As a smoking cessation adviser some of my patients are on nicotine patches for the short term, meaning not more than 11/52 with continuous monitoring of their capillary blood level post postprandial. HBA1c 3/12 after quitting" - Lovina Fox-cobham, London
"Think about the effect on them, will now be specific re persistent effect on blood sugar level, the key to minimising effects" - Una Duffy, Surrey