Calcium in the blood could provide an early warning of certain cancers, especially in men, research has shown.
Even slightly raised blood levels of calcium in men was associated with an increased risk of cancer diagnosis within one year.
The discovery, reported in the British Journal of Cancer, raises theprospect of a simple blood test to aid the early detection of cancer in high risk patients.
Hypercalcaemia - a higher than normal calcium reading - was associated with a wide range of cancers, chiefly lung, prostate, breast, bowel, and those affecting the blood such as leukaemia and myeloma.
While the condition was already known to occur in up to a fifth of cancer patients, this is the first time it has been shown to pre-date diagnosis.
Lead researcher Dr Fergus Hamilton, of the Centre for Academic Primary Care at the University of Bristol, said: "All previous studies on hypercalcaemia and cancer had been carried out with patients who had already been diagnosed with cancer - hypercalcaemia was seen as a late effect of the cancer."
The Bristol team analysed the records of 54,000 patients listed on an electronic GP database to see how many with a history of hypercalcaemia went on to receive a cancer diagnosis.
A normal level of calcium in the blood is between 2.1 and 2.5 millimoles a litre (mmol/L).
In men, even a slight increase outside this range (2.6-2.8 mmol/L) was found to increase the risk of cancer being diagnosed within one year by 11.5 per cent. Above 2.8 mmol/L, the risk rose to 28 per cent.
The effect was much smaller in women, with similar calcium elevations increasing cancer risk by 4.1 per cent and 8.7 per cent respectively.
One reason for the difference could be that women are more likely to experience hypercalcaemia due to overactive parathyroid glands, which has nothing to do with cancer. In the study, this would make the link with cancer less noticeable in women.
"We were surprised by the gender difference," said Dr Hamilton.
"There are a number of possible explanations for this but we think it might be because women are much more likely to have hyperparathyroidism, another cause of hypercalcaemia. Men rarely get this condition, so their hypercalcaemia is more likely to be due to cancer."
