The finding may shed light on development of meningiomas, tumours arising from the brain and spinal cord that are usually not cancerous but that can require risky surgery and affect a patient's quality of life, researchers said.

Since previous research had established that the slow-growing tumours are more common among people who are obese and those who have diabetes, researchers led by Judith Schwartzbaum from Ohio State University in the US set out to look for a relationship between meningiomas and blood markers, including glucose.

High blood sugar is a component of diabetes and a precursor to its development. Type 2 diabetes and obesity are closely linked, researchers said.

However, when they compared blood tests in a group of more than 41,000 Swedes with meningioma diagnoses 15 or fewer years later, they found that high blood sugar, particularly in women, actually meant the person was less likely to face a brain tumour diagnosis.

"It's so unexpected. Usually diabetes and high blood sugar raises the risk of cancer, and it's the opposite here," said Schwartzbaum.

"It should lead to a better understanding of what's causing these tumours and what can be done to prevent them," she said.

Though meningiomas are rarely cancerous, they behave in a similar way, leading scientists to wonder if some relationships between possible risk factors and tumour development would be similar, Schwartzbaum said.

The researchers, looking at data collected from 1985 to 2012, identified 296 cases of meningioma, more than 61 percent of them in women.

Women with the highest fasting blood sugar were less than half as likely as those with the lowest readings to develop a tumour.

The relationship was not statistically significant when researchers looked at men's fasting sugar readings and tumour development.

However, when they compared the less-reliable non-fasting sugar readings (those taken without a period of no food or drink that could influence the results), they found that both men and women with high blood sugar had a lower likelihood of meningioma diagnosis.

A diabetes diagnosis before meningioma also appeared to decrease the risk of this tumour, although Schwartzbaum said the data likely had incomplete information on diabetes.

The results could lead to a clearer explanation of how the tumours develop and grow and could potentially start researchers down the road to improved diagnostic techniques, Schwartzbaum said.

The research appears in the British Journal of Cancer.

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