A new study has suggested that men need the female hormone oestrogen to maintain their sex drive and help prevent obesity.

The research, conducted at Massachuetts General Hospital, says that men who have low levels of oestrogen can show ‘male menopause’ symptoms such as low libido and have little interest in sex. They are also increasingly likely to put on weight.

The problems men have as they age are thought to be caused by a lack of testosterone, when it seems it could actually be due to low oestrogen levels.

The study involved 400 healthy men, aged 20 to 50, who were given monthly injections of a drug to temporarily reduce their testosterone levels.

The volunteers were also given a testosterone gel to use and half of the group were also given a second drug which stops testosterone’s conversion into oestrogen.

Structure of the oestrogen hormone

This then allowed the researchers to compare the different levels of both hormones on strength and body composition.

After 16 weeks, researchers could see that muscle size and strength was dependant on testosterone while body-fat mass needed oestrogen. Both hormones were required to help maintain a sex drive.

The results are identical to the same tests done on animals. Mice that are altered so they do not make the oestrogen hormone become fat and have no sex drive. 

Unfortunately, the new study was too short to see long term benefits and risks, for example the impact of testosterone supplements on the heart, cancer and mental sharpness.

"This is a big public health issue," said Dr Joel Finkelstein of Massachusetts General Hospital. "If the changes with aging are due to these things, then potentially replacing these hormones in men might ameliorate these changes."