A diabetes pen similar to the one pictured can be used to draw blood for tests Getty

Heightened levels of the hormone testosterone have been linked to a raised risk of diabetes and enlarged prostates, according to a new study.

Saliva tests conducted by University of California scientists, on 350 adult men of the Tsimane tribe, which lives in the Bolivian rainforest, found they had almost non-existent levels of prostate enlargement.

In a report published on diabetes.co.uk, the researchers also found that the Tsimane had low levels of testosterone and glucose in their blood, which means a reduced risk of developing diabetes.

The researchers discovered that tribe members who did have higher levels of testosterone had larger prostates. The researchers also found that those with larger prostates also had higher HbA1c levels.

University of California Professor Michael Gurven, wrote in the Journal of Gerontology: "Type 2 [adult onset] diabetes is one of these illnesses that under more traditional conditions wouldn't be as prevalent as it is today in high-income countries, or becoming increasingly prevalent in urban areas of low-income countries.

"As groups of the Tsimane undergo change, we might very well see an increase in diabetes."

Dr Benjamin Trumble, also of the university's anthropology department, added: "Among men with low testosterone and low diabetes risk, those with relatively higher testosterone or HbA1c were at higher risk of prostate enlargement."