Men should be careful when considering moving country, for a new study suggests that it could affect their libido and susceptibility to disease by changing their testosterone levels.
Sex hormones, such as testosterone and oestradiol, are involved in a number of age-related health problems, including cancers and loss of bone strength. However, vulnerability to these diseases varies from country to country.
For instance, men in Asia are less likely to develop prostate cancer than those living in the US or Europe.
To determine whether varying levels of sex hormones might explain these differences, Jane Cauley at the University of Pittsburgh in Pennsylvania and colleagues compared levels of testosterone and oestradiol in blood samples from 5000 men over the age of 65 from Hong Kong, Japan, Sweden, Tobago and the US.
After adjusting for the men's age and body mass, Cauley's team identified a number of differences between them, reports New Scientist.
While total testosterone levels were similar in men from Sweden, Tobago and the US, they were 16 per cent higher in men from Hong Kong and Japan.
The Japanese men also had higher levels of a testosterone-binding hormone, however, so less of the testosterone was free to act on tissues. As a result, Japanese men had the lowest levels of active testosterone.
However, Asian men who had moved to the US had similar testosterone levels to residents of European descent, suggesting that environment had an influence. Diet could play a role, suggests Cauley.
When the team looked at levels of free oestradiol they found they were between 10 and 16 per cent higher in men of African ancestry living in Tobago or the US than in any other group.
The team says this suggests a genetic influence. Japanese men, on the other hand, had relatively low levels of free oestradiol.
Such variation in sex hormones could have many implications for men's health.
The study appears in the Journal of Clinical Endocrinology and Metabolism.