Calcium in the blood could provide an early warning of certain cancers, especially in men, research has shown.
Even slightly raised levels of calcium in men was associated with an increased risk of cancer diagnosis within one year.
The discovery raises the prospect of a blood test to aid the early detection of cancer in high-risk patients.
Hypercalcaemia - a higher than normal calcium reading - was associated with cancers, chiefly lung, prostate, breast, bowel and those affecting the blood.
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.
Dr Fergus Hamilton, from the University of Bristol, said: "All previous studies had been carried out with patients who had already been diagnosed with cancer - hypercalcaemia was seen as a late effect of it.
"We wanted to look at the issue from a different perspective and find out if high calcium levels in blood could be used as an early indicator of cancer and, therefore, in the diagnosis of cancer."
A normal level of calcium in the blood is between 2.1 and 2.5 millimoles per litre (mmol/L)
In men, even a slight increase outside this range (2.6 to 2.8 mmol/L) was found to increase the risk of cancer being diagnosed within one year by 11.5pc. Above 2.8 mmol/L, the risk rose to 28pc.