Sexual problems in men may be linked to low levels of the hormone prolactin, according to a new study. The finding is perhaps surprising because experts have traditionally thought prolactin, which stimulates breast development and milk production in women, impairs men's sexual functioning at high levels.
In the new study, researchers looked at nearly 3,000 European men ages 40 to 79, and measured their testosterone and prolactin levels, body mass indexes (BMIs), and blood cholesterol and sugar levels. The participants filled out questionnaires about their general health, smoking, alcohol consumption and sexual functioning.
The results showed low prolactin was linked to several signs of poor sexual health, as well psychological health. Men with levels of prolactin that were lower than average, although still within the normal range, were more likely than men with higher levels to say their sexual function was getting worse, particularly their enjoyment of orgasm. They also had more symptoms of depression, the researchers said.
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Low prolactin was also associated with higher BMI and blood sugar, lower levels of physical activity, and generally feeling unhealthier, according to the study published Oct. 29 in the Journal of Sexual Medicine.
Prolactin is best known for its importance in enabling women to produce breast milk after delivering a baby. During pregnancy and breast-feeding, prolactin levels are 10 to 20 times higher than at other times.
Men and non-pregnant women also produce prolactin, but it's not clear what the hormone does in these people. Studies have found that high prolactin levels in men are linked to low sexual desire and erectile dysfunction, and men suffering from such conditions are sometimes tested for high prolactin levels.
The new findings, however, are in contrast with the well-accepted idea that high prolactin levels are linked with men's sexual problems, the researchers said. In fact, the results suggest that prolactin might have a more positive, rather than negative, effect in initiating or maintaining male sexual behavior. [Macho Man: 10 Wild Facts About His Body]
Some previous research supports the new finding, the researchers said. Two animal studies have shown that using drugs to increase prolactin levels in rats boosted their sexual behavior. And a brain-imaging study of men who looked at erotic pictures showed that higher levels of prolactin were associated with more activity in brain regions responding to sexual arousal.
However, it's still unclear how prolactin may facilitate men's sexual functioning, and the study doesn't prove a cause-and-effect relationship, the researchers said.
It is possible that low prolactin mirrors a change in the levels of signaling chemicals in the brain that regulate sexual behavior. It is also possible that overall poorer health is the underlying reason for low prolactin and lower sex drive, the researchers said.
Email Bahar Gholipour. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.
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